Vba excel с базой данных

Работа с внешними источниками данных

Материалы по работе с внешними источниками данных на примере Excel и SQL.

Рассмотрим способы передачи данных между Excel и внешней базой данной на SQL сервере с помощью ADO.

Задача первая. Подключаемся к внешней базе данных.

Для начала надо подключиться к внешней базе данных. Подключение возможно если на компьютере установлен драйвер. Список установленных драйверов для подключения к базам данных на компьютере под управлением Windows:

Панель управленияВсе элементы панели управленияАдминистрированиеИсточники данных (ODBC)

Проверить подключение к базе данных можно простым способом. Создаем пустой файл (например, «текстовый документ.txt»), затем изменяем имя и расширение на .udl (например, «connect.udl»). Двойной клик мышкой по новому файлу, далее приступаете к настройке и проверке подключения к базе данных. После того, как удалось настроить корректное подключение к базе данных, сохраняем файл «connect.udl». Открываем файл «connect.udl» обычным текстовым редактором (например, блокнотом), и видим в строке подключения все необходимые параметры. Про подключение к внешним базам данных можно посмотреть на ресурсе ConnectionStrings .

Теперь возвращаемся к нашему VBA для Excel. В редакторе VBA подключаем последнюю версию библиотеки:

 Microsoft ActiveX Data Objects Library

Пример кода:

Sub TestConnection()
Dim cn As ADODB.Connection
Set cn = New ADODB.Connection
cn.ConnectionString = "" 'Параметры строки подключения
cn.Open   'Открываем подключение
cn.Close   'Закрываем подключение
Set cn = Nothing   'Стираем объект из памяти
End Sub

Задача вторая. Загружаем данные из внешней базы данных на SQL сервере в Excel.

После того, как мы установили подключение к внешней базе данных можно приступать к чтению данных и выводу в Excel. Здесь потребуется знание языка запросов SQL. В результате выполнения SQL запроса к нам возвращается некая таблица с данными в объект RecordSet. Далее из объекта RecordSet можно выгружать данные непосредственно на лист или в сводную таблицу.

Пример кода простой процедуры:

Sub LoadData()

Dim cn As ADODB.Connection
Dim rst As ADODB.Recordset

Set cn = New ADODB.Connection
Set rst = New ADODB.Recordset

cn.ConnectionString = "" 'Параметры строки подключения
cn.Open

rst.Open "SELECT TOP 10 * FROM <таблица>", cn 'SQL-запрос, подключение

ActiveSheet.Range("A1").CopyFromRecordset rst 'Извлекаем данные на лист

rst.Close
cn.Close

Set rst = Nothing
Set cn = Nothing

End Sub

Для удобства работы. Предлагаю создать собственный класс «tSQL» для работы с базой данных.  У класса будет одно свойство:

Public ConnectionSring As String

Для чтения данных напишем метод SelectFrom с параметрами TableName и ws. TableName — это имя таблицы, откуда будем считывать данные и ws — лист Excel, куда будем записывать данные.

Public Sub SelectFrom(TableName As String, ws As Worksheet)

Dim cn As ADODB.Connection
Dim rst As ADODB.Recordset
Dim SQLstring As String
Dim i As Long

Set cn = New ADODB.Connection
Set rst = New ADODB.Recordset
SQLstring = "SELECT * FROM " & TableName
ws.Cells.Clear

cn.ConnectionString = ConnectionSring
cn.Open

rst.Open SQLstring, cn

For i = 1 To rst.Fields.Count
 ws.Cells(1, i) = rst.Fields(i - 1).Name
Next i
ws.Range("A2").CopyFromRecordset rst

rst.Close
cn.Close

Set rst = Nothing
Set cn = Nothing
SQLstring = Empty
i = Empty

End Sub

Пример использования класса tSQL в процедуре

Sub mySQL()
Dim ts As tSQL
Set ts = New tSQL

ts.ConnectionSring = '<Строка подключения>
ts.SelectFrom "Название таблицы", ActiveSheet

Set ts = Nothing
End Sub

Задача третья. Загружаем данные из Excel во внешнюю базу данных.

Для записи данных напишем метод InsertInto с параметрами TableName. rHead и rData. TableName — это имя таблицы, куда будем добавлять данные;  rHead — диапазон ячеек, с указанием полей; rData — диапазон ячеек с данными, которые будем добавлять.

Public Sub InsertInto(TableName As String, rHead As Range, rData As Range)

Dim cn As ADODB.Connection
Dim SQLstring As String
Dim SQLstringH As String
Dim SQLstringV As String
Dim i As Long
Dim j As Long

Dim arrHead()
Dim arrData()

arrHead = rHead.Value
arrData = rData.Value
Set cn = New ADODB.Connection
cn.ConnectionString = ConnectionSring
cn.Open

SQLstringH = "INSERT INTO " & TableName & "("
For j = LBound(arrHead, 2) To UBound(arrHead, 2)
 SQLstringH = SQLstringH & " " & arrHead(1, j)
 If j < UBound(arrHead, 2) Then
 SQLstringH = SQLstringH & ","
 Else
 SQLstringH = SQLstringH & ")"
 End If
Next j
SQLstringH = SQLstringH & " VALUES("

For i = LBound(arrData, 1) To UBound(arrData, 1)
 For j = LBound(arrData, 2) To UBound(arrData, 2)
 SQLstringV = SQLstringV & " " & arrData(i, j)
 If j < UBound(arrHead, 2) Then
 SQLstringV = SQLstringV & ","
 Else
 SQLstringV = SQLstringV & ") "
 End If
 Next j
 SQLstring = SQLstringH & SQLstringV
 SQLstringV = Empty
 cn.Execute SQLstring
Next i
cn.Close

Set cn = Nothing
SQLstring = Empty
i = Empty
j = Empty
SQLstring = Empty
SQLstringH = Empty
SQLstringV = Empty
Erase arrHead
Erase arrData

End Sub

Пример использования класса tSQL в процедуре

Sub mySQL()
Dim ts As tSQL
Set ts = New tSQL

ts.ConnectionSring = '<Строка подключения>
ts.InsertInto "Название таблицы", Range("B1:D1"), Range("B8:D300")

Set ts = Nothing
End Sub

Задача четвертая. Управляем внешней базой данных из Excel

Рекомендую использовать запросы в основном для чтения данных из внешней БД. Можно записывать данные в таблицы внешней БД.
Но крайне не желательно использовать Excel для управления внешней базой данных, лучше использовать стандартные средства разработки.

Полезные ссылки:

Data from Excel to SQL 

 http://www.excel-sql-server.com/excel-sql-server-import-export-using-vba.htm

При упоминании баз данных (БД) первым делом, конечно, в голову приходят всякие умные слова типа SQL, Oracle, 1С или хотя бы Access. Безусловно, это очень мощные (и недешевые в большинстве своем) программы, способные автоматизировать работу большой и сложной компании с кучей данных. Беда в том, что иногда такая мощь просто не нужна. Ваш бизнес может быть небольшим и с относительно несложными бизнес-процессами, но автоматизировать его тоже хочется. Причем именно для маленьких компаний это, зачастую, вопрос выживания.

Для начала давайте сформулируем ТЗ. В большинстве случаев база данных для учета, например, классических продаж  должна уметь:

• хранить в таблицах информацию по товарам (прайс), совершенным сделкам и клиентам и связывать эти таблицы между собой
• иметь удобные формы ввода данных (с выпадающими списками и т.п.)
• автоматически заполнять этими данными какие-то печатные бланки (платежки, счета и т.д.)
• выдавать необходимые вам отчеты для контроля всего бизнес-процесса с точки зрения руководителя

Со всем этим вполне может справиться Microsoft Excel, если приложить немного усилий. Давайте попробуем это реализовать.

Шаг 1. Исходные данные в виде таблиц

Информацию о товарах, продажах и клиентах будем хранить в трех таблицах (на одном листе или на разных — все равно). Принципиально важно, превратить их в «умные таблицы» с автоподстройкой размеров, чтобы не думать об этом в будущем. Это делается с помощью команды Форматировать как таблицу на вкладке Главная (Home — Format as Table). На появившейся затем вкладке Конструктор (Design) присвоим таблицам наглядные имена в поле Имя таблицы для последующего использования:

Итого у нас должны получиться три «умных таблицы»:

Обратите внимание, что таблицы могут содержать дополнительные уточняющие данные. Так, например, наш Прайс содержит дополнительно информацию о категории (товарной группе, упаковке, весу и т.п.) каждого товара, а таблица Клиенты — город и регион (адрес, ИНН, банковские реквизиты и т.п.) каждого из них.

Таблица Продажи будет использоваться нами впоследствии для занесения в нее совершенных сделок.

Шаг 2. Создаем форму для ввода данных

Само-собой, можно вводить данные о продажах непосредственно в зеленую таблицу Продажи, но это не всегда удобно и влечет за собой появление ошибок и опечаток из-за «человеческого фактора». Поэтому лучше будет на отдельном листе сделать специальную форму для ввода данных примерно такого вида:

В ячейке B3 для получения обновляемой текущей даты-времени используем функцию ТДАТА (NOW). Если время не нужно, то вместо ТДАТА можно применить функцию СЕГОДНЯ (TODAY).

В ячейке B11 найдем цену выбранного товара в третьем столбце умной таблицы Прайс с помощью функции ВПР (VLOOKUP). Если раньше с ней не сталкивались, то сначала почитайте и посмотрите видео тут.

В ячейке B7 нам нужен выпадающий список с товарами из прайс-листа. Для этого можно использовать команду Данные — Проверка данных (Data — Validation), указать в качестве ограничения Список (List) и ввести затем в поле Источник (Source) ссылку на столбец Наименование из нашей умной таблицы Прайс:

Аналогичным образом создается выпадающий список с клиентами, но источник будет уже:

=ДВССЫЛ(«Клиенты[Клиент]»)

Функция ДВССЫЛ (INDIRECT) нужна, в данном случае, потому что Excel, к сожалению, не понимает прямых ссылок на умные таблицы в поле Источник. Но та же ссылка «завернутая» в функцию ДВССЫЛ работает при этом «на ура» (подробнее об этом было в статье про создание выпадающих списков с наполнением).

Шаг 3. Добавляем макрос ввода продаж

После заполнения формы нужно введенные в нее данные добавить в конец таблицы Продажи. Сформируем при помощи простых ссылок строку для добавления прямо под формой:

Т.е. в ячейке A20 будет ссылка =B3, в ячейке B20 ссылка на =B7 и т.д.

Теперь добавим элементарный макрос в 2 строчки, который копирует созданную строку и добавляет ее к таблице Продажи. Для этого жмем сочетание Alt+F11 или кнопку Visual Basic на вкладке Разработчик (Developer). Если эту вкладку не видно, то включите ее сначала в настройках Файл — Параметры — Настройка ленты (File — Options — Customize Ribbon). В открывшемся окне редактора Visual Basic вставляем новый пустой модуль через меню Insert — Module и вводим туда код нашего макроса:

Sub Add_Sell()
    Worksheets("Форма ввода").Range("A20:E20").Copy                         'копируем строчку с данными из формы
    n = Worksheets("Продажи").Range("A100000").End(xlUp).Row                'определяем номер последней строки в табл. Продажи
    Worksheets("Продажи").Cells(n + 1, 1).PasteSpecial Paste:=xlPasteValues 'вставляем в следующую пустую строку
    Worksheets("Форма ввода").Range("B5,B7,B9").ClearContents               'очищаем форму
End Sub

Теперь можно добавить к нашей форме кнопку для запуска созданного макроса, используя выпадающий список Вставить на вкладке Разработчик (Developer — Insert — Button):

После того, как вы ее нарисуете, удерживая нажатой левую кнопку мыши, Excel сам спросит вас — какой именно макрос нужно на нее назначить — выбираем наш макрос Add_Sell. Текст на кнопке можно поменять, щелкнув по ней правой кнопкой мыши и выбрав команду Изменить текст.

Теперь после заполнения формы можно просто жать на нашу кнопку, и введенные данные будут автоматически добавляться к таблице Продажи, а затем форма очищается для ввода новой сделки.

Шаг 4. Связываем таблицы

Перед построением отчета свяжем наши таблицы между собой, чтобы потом можно было оперативно вычислять продажи по регионам, клиентам или категориям. В старых версиях Excel для этого потребовалось бы использовать несколько функций ВПР (VLOOKUP) для подстановки цен, категорий, клиентов, городов и т.д. в таблицу Продажи. Это требует времени и сил от нас, а также «кушает» немало ресурсов Excel. Начиная с Excel 2013 все можно реализовать существенно проще, просто настроив связи между таблицами.

Для этого на вкладке Данные (Data) нажмите кнопку Отношения (Relations). В появившемся окне нажмите кнопку Создать (New) и выберите из выпадающих списков таблицы и названия столбцов, по которым они должны быть связаны:

Важный момент: таблицы нужно задавать именно в таком порядке, т.е. связанная таблица (Прайс) не должна содержать в ключевом столбце (Наименование) повторяющихся товаров, как это происходит в таблице Продажи. Другими словами, связанная таблица должна быть той, в которой вы искали бы данные с помощью ВПР, если бы ее использовали.

Само-собой, аналогичным образом связываются и таблица Продажи с таблицей Клиенты по общему столбцу Клиент:

После настройки связей окно управления связями можно закрыть, повторять эту процедуру уже не придется.

Шаг 5. Строим отчеты с помощью сводной

Теперь для анализа продаж и отслеживания динамики процесса, сформируем для примера какой-нибудь отчет с помощью сводной таблицы. Установите активную ячейку в таблицу Продажи и выберите на ленте вкладку Вставка — Сводная таблица (Insert — Pivot Table). В открывшемся окне Excel спросит нас про источник данных (т.е. таблицу Продажи) и место для выгрузки отчета (лучше на новый лист):

Жизненно важный момент состоит в том, что нужно обязательно включить флажок Добавить эти данные в модель данных (Add data to Data Model) в нижней части окна, чтобы Excel понял, что мы хотим строить отчет не только по текущей таблице, но и задействовать все связи.

После нажатия на ОК в правой половине окна появится панель Поля сводной таблицы, где нужно щелкнуть по ссылке Все, чтобы увидеть не только текущую, а сразу все «умные таблицы», которые есть в книге.А затем можно, как и в классической сводной таблице, просто перетащить мышью нужные нам поля из любых связанных таблиц в области Фильтра, Строк, Столбцов или Значений — и Excel моментально построит любой нужный нам отчет на листе:

Не забудьте, что сводную таблицу нужно периодически (при изменении исходных данных) обновлять, щелкнув по ней правой кнопкой мыши и выбрав команду Обновить (Refresh), т.к. автоматически она этого делать не умеет.

Также, выделив любую ячейку в сводной и нажав кнопку Сводная диаграмма (Pivot Chart) на вкладке Анализ (Analysis) или Параметры (Options) можно быстро визуализировать посчитанные в ней результаты.

Шаг 6. Заполняем печатные формы

Еще одной типовой задачей любой БД является автоматическое заполнение различных печатных бланков и форм (накладные, счета, акты и т.п.). Про один из способов это сделать, я уже как-то писал. Здесь же реализуем, для примера, заполнение формы по номеру счета:

Предполагается, что в ячейку C2 пользователь будет вводить число (номер строки в таблице Продажи, по сути), а затем нужные нам данные подтягиваются с помощью уже знакомой функции ВПР (VLOOKUP) и функции ИНДЕКС (INDEX).

Ссылки по теме

• Как использовать функцию ВПР (VLOOKUP) для поиска и подстановки значений
• Как заменить ВПР функциями ИНДЕКС и ПОИСКПОЗ
• Автоматическое заполнение форм и бланков данными из таблицы
• Создание отчетов с помощью сводных таблиц

ORM переводится, как object relational mapping (объектно-реляционное отображение). Это означает, что мы работаем с базой не на уровне SQL запросов, а на уровне объектов.

Давайте я покажу пример и как это будет работать в итоге.

Для начала скажу, что у меня есть база «SQL Server 2016» серьезная база для промышленной реализации, но не пугайтесь она так же доступна простым смертным. Где её скачать расскажу позже.

Каждый раз для использования нашей ORM необходимо объявить и инициализировать несколько переменных c типом DataBase, RecordSet, UnitOfWork. И соединить их с помощью метода Init.

Давайте объявим эти переменные.

Dim db As New DataBase
Dim Rs As New ADODB.Recordset
Dim uow As New unitOfWork

uow.Init db, Rs

Давайте посмотрим, как получить данные.

Для этого объявим переменную с типом User. И реализуем цикл с помощью метода GetAll . Посмотрите, как удобно получать данные о пользователях. Всё что нам надо это просто вызвать метод GetAll в свойстве UserRepository. Точно такие же репозитории будут добавляться и для других типов данных, например, некие документы или накладные InvoiceRepository. После чего в самом цикле мы переберем всех пользователи из базы и выведем их в консоль.

В цикле можно перебрать любые данные. Использовать такие методы, как GetAll очень удобно. Мы не заморачиваемся с SQL запросами и получаем объект определенного типа, свойства и методы которого можно получить и увидеть через IntelliSence. Свойства полученного объекта в нашем примере это Id, Email, UserName объект пока не содержит методов только свойства.

Теперь давайте посмотрим, как добавить запись в базу

Фактически всё что нам нужно это создать объект и задать этому объекту новые значения.

Потом добавить объект через метод “Add”, который есть у любых коллекций и зафиксировать изменения в базе через метод “uow.Commit”.

Если мы запустим наш цикл, который выводил данные мы увидим нашу новую запись.

Та же самая запись сохранилась в базе. При этом Id добавился автоматически, т.е. Id это так называемый первичный ключ в базе, который сама база добавляет автоматически.

И в этом примере добавление данных выглядит крайне удобно и вполне естественно. Создаем объект пользователь, задаем ему значения свойств и добавляем в репозиторий. Всё!

Итак, теперь подробнее про саму реализацию ORM.

Для работы с этим примером нам потребуется несколько программ. Первая программа — это SQL Server 2016. Вы сможете найти её по адресу (https://www.microsoft.com/en-us/sql-server/application-development). Также для работы нам потребуется Management studio (https://docs.microsoft.com/en-us/sql/ssms/download-sql-server-management-studio-ssms). Выберите и нажмите ссылку в зависимости от вашего языка.

В ООП есть специальные шаблоны проектирования, чтобы другие программисты, увидев их понимали, что мы написали и как работает наша программа.

В данном случае у нас есть шаблон проектирования – репозиторий его суть — это удобное переключение баз данных, получение данных в объектном стиле. В моем примере мы работаем с SQL Server 2016, но с шаблоном проектирования репозиторий мы можем поменять базу, например, на MySql или MS Access довольно просто. При этом наша основная логика не пострадает.

Теперь, давайте посмотрим пример поподробнее. Для того, чтобы реализовать шаблон нам надо несколько классов сам репозиторий. В моем примере это – UserRepository. Класс, который объединяет репозитории это класс UnitOfWork. И классы, которые соответствуют таблицам в базе данных такие классы называют модели данных. Они же в идеале должны содержать большую часть логики (которые обычно реализуются через методы), так называемая, богатая модель. Если модель не содержит логики т.е. методов, то её принято называть ананимичная модель т.е. бедная. В моем простом примере нет пока логики, поэтому модель «User» пока можно отнести к ананимичной модели данных.

И так давайте посмотрим на модель User. В классе добавлено три псевдосвойства Id, Email, UserName. У меня есть отдельное видео рассказывающее про эти свойства. Те же самые поля у меня определенны в базе данных. В Management Studio я создал простую базу TestDb и добавил таблицу User. В исходниках у Вас будет SQL файл с запросом на создание этой таблицы. Просто запустите его в своей Management Studio.

Либо в Management Studio добавьте таблицу, нажав правую кнопку -> New -> Table. И добавьте поля Id, Email, UserName. Для Id добавьте тип данных bigint, для Email nvarchar(50), для UserName nvarchar(50).

Потом нажмите правую кнопку мышки по полю Id и выберите “Set primarity key” (добавить). Это тот самый первичный ключ, который автоматически увеличивается при каждом добавлении данных в базу.

Поэтому в свойствах поля проставьте инкремент полю Id, чтобы при каждом добавление записей в таблицу поле Id автоматически увеличивалось на единицу.

UnitOfWork

Давайте теперь посмотрим класс UnitOfWork

Данный класс в основном должен содержать только репозитории и метод Commit для сохранения данных в базе. И может содержать несколько вспомогательных членов.

В моем примере я добавил метод Init, чтобы через этот метод можно было внедрить объекты типа DataBase и Recordset. Т.к. в стандартном конструкторе на VBA нет возможности передать параметры. Такой механизм передачи объектов извне класса называется внедрение зависимостей.

Private pUserRepository As UserRepository

Public Function Init(DataBase As DataBase, Recordset As ADODB.Recordset)
    Set pUserRepository = New UserRepository
    Set pUserRepository.DataBase = DataBase
    Set pUserRepository.Recordset = Recordset
End Function

Public Connection As New ADODB.Connection
Private pStr As String


Private Sub Class_Initialize()
    pStr = "Driver={SQL Server Native Client 11.0};Server=localhost;Database=TestDb;Trusted_Connection=yes;"
    Connection.ConnectionString = pStr
    If Connection.State = 0 Then
        Connection.Open
    End If
End Sub

Друзья я еще не рассказывал, как работать с базами через библиотеку ADODB. Если вы хотите более подробный урок по этой теме просто напишите мне или пролайкайет видео.

Репозиторий (UserRepository)

Сам репозиторий довольно простой для начала я добавил три публичных свойства, чтобы был доступ к самой базе SQL Server через объект типа DataBase. Добавил свойство RecordSet для работы с ним внутри метода GetAll. В принципе сам класс UserRepositroy можно запускать независимо, но для реализации шаблона я инициализирую репозиторий в классе UnitOfWork.

Public LocalUsers As New Collection
Public DataBase As DataBase
Public Recordset As ADODB.Recordset

И далее два основных метода. Метод GetAll и метод Add. Метод GetAll просто получает все записи из базы данных и переводит их в объект коллекцию типа User c помощью встроенного объекта RecordSet. Внутри метода я запускаю SQL запрос на выборку нужных мне полей. А далее через объект RecorSet получаю их.

Public LocalUsers As New Collection
Public DataBase As DataBase
Public Recordset As ADODB.Recordset


Public Function GetAll() As Collection
    Dim selectAllQuery As String:
    selectAllQuery = "Select Id, Email, UserName from [User]"
    
    If DataBase Is Nothing Then MsgBox "DataBase not found set it"
    If Recordset Is Nothing Then MsgBox "RecordSet not found set it"
    Recordset.Open selectAllQuery, DataBase.Connection
    
    Dim userCollection As New Collection
    Dim user As user
    With Recordset
        While (Not .EOF)
            Set user = New user
            
            user.Id = .Fields(0).Value
            user.Email = .Fields(1).Value
            user.UserName = .Fields(2).Value
            
            userCollection.Add user
            
            .MoveNext
        Wend
    End With
    
    Recordset.Close
    Set GetAll = userCollection
End Function

Public Function Add(user As user)
    LocalUsers.Add user
End Function

Connecting to Microsoft Access Database from Excel VBA, using DAO Object Model

Microsoft Access: Data Access Objects Library (DAO), Connect with Access Databases from Excel using VBA.

Part 1 of 3

Microsoft Access: Data Access Objects Library (DAO), Connect with Access Databases from Excel using VBA

1. Connecting to Microsoft Access Database from Excel VBA, using DAO Object Model.

2. Microsoft Access DAO Object Model: Create an Index, Create Relationship between Fields, Create and Execute a Query.

3. Microsoft Access DAO Object Model: Import or Export Data from Access to Excel.

—————-

Also Read:

Microsoft Access: ActiveX Data Objects (ADO), Connect with Access Databases from Excel using VBA.

————————————————————————————

Contents:

Connect with Databases using DAO, RDO and ADO Objects

DAO Objects & Programming model

The DBEngine object & Workspace Object

DAO Databases

Tables of a DAO Database

Fields / Columns of a Table

Recordset & Records of a DAO Database Table

————————————————————————————

To connect with other databases, when working in VBA, you can use either DAO (Data Access Objects), RDO (Remote Data Objects) or ADO (ActiveX Data Objects). After connecting to a database, you can manipulate its data. DAO, RDO and ADO are data access interfaces ie. they are object and programming models used to access data. Earlier, DAO was used to interface with local databases (viz. MS Access), RDO was used to interface with large databases such as Oracle and SQL Server. ADO was their replacement to interface with all types of data sources. Both DAO and ADO are commonly used while connecting to Microsoft Access Database.

This section explains using the DAO Objects & Programming model to Connect with Access Databases from Microsoft Excel, the DBEngine object, Workspace Object & Workspaces Collection, DAO Databases, Tables of a DAO Database, Fields / Columns of a Table, Recordset & Records of a DAO Database Table, with practical examples.

Connect with Databases using DAO, RDO and ADO Objects

To connect with other databases, when working in VBA, you can use either DAO (Data Access Objects), RDO (Remote Data Objects) or ADO (ActiveX Data Objects). After connecting to a database, you can manipulate its data.

DAO, RDO and ADO are data access interfaces ie. they are object and programming models used to access data. Earlier, DAO was used to interface with local databases (viz. MS Access), RDO was used to interface with large databases such as Oracle and SQL Server. ADO was their replacement to interface with all types of data sources. Both DAO and ADO are commonly used while connecting to Microsoft Access Database. DAO is native to Access, the DAO object library is the default reference in Access 2007 and the library will be existing when you use Access (ADO object library was the default reference in Access 2000 and 2002, whereas DAO returned as the default object library with Access 2003 after being the default in Access 97 earlier). DAO integrates well with Access databases and provides faster access. ADO provides access to a wider variety of data sources than DAO, besides Access. ADO has succeeded DAO and is the latest data access technology, is simpler and more flexible, and interfaces with Microsoft’s powerful data access technology of OLE DB. In ADO the objects are less than in DAO, and it contains more properties, methods and events. ADO/OLE DB is recommended for new projects but it might not be worthwhile to convert DAO code to ADO for existing projects.

ADO creates a reference to the database using the Connection object, to connect to the data source. You use the Open and Close methods to open and close a Connection object. DAO creates a reference to the database using the database object, to connect to the data source.

In Microsoft Access, Recordset objects are used to access and manipulate data in a database. A Recordset object represents a set of records in a database table, or a set of records returned from running a query. Both DAO and ADO libraries have a Recordset object, though the methods, properties, and options of the respective object is different. A Record object is one row of data in a Recordset. A Recordset object has a Fields collection which contains all the Field objects, where each Field object represents a column in the Recordset. In other words, each record represents a row of data and contains many fields, and each field corresponds to a column in the database table.

In your VBA code, you should ideally precede the object name by its program ID (ProgID) prefix, which in ADO is «ADODB» and in DAO is «DAO». Many objects, for example the Recordset object, have similar names in both DAO and ADO and it is advisable to have explicit references in your project. This becomes a must if you have included references to both the DAO and ADO libraries in your VBA project, else the object library mentioned first in the References list will prevail, resulting in confusion in the vba code.

While instantiating the Recordset object, you should use:

Dim daoRecSet As DAO.Recordset

Dim adoRecSet As ADODB.Recordset

instead of:

Dim RecSet As Recordset

DAO Objects & Programming model

DAO (Data Access Objects) is an object-oriented data access interface, used to connect to and access databases. It was the first Objects & Programming model which used the Microsoft Jet database engine, and is optimized to work Microsoft Access files (.mdb). The objects and collections in the DAO object hierarchy are used to connect to a database, access and manipulate its data and database structure.

A database engine is the underlying software component of a database used to manipulate its data. DAO Object Model by default uses the Microsoft Jet database engine for data access. ODBCDirect (which came after ODBC) allowed DAO to access ODBC data sources directly without using the Jet database engine. In this section we will illustrate connecting to Microsoft Access Database using DAO with the Jet engine. Prior to Access 2007, Access used the Microsoft (JET) engine, but with Access 2007 the new and improved ACE engine has succeeded and replaced JET. The ACE engine is fully backward-compatible so that it can be used with the .accdb files (Access 2007) and the earlier .mdb files.

Automating Access from Excel: You can connect to and access a database using DAO, from external applications which support automation (viz. MS Excel, MS Word, etc.), and in this section we show how to do this from Microsoft Excel by using VBA. With automation you can control another application (MS Access) within your host application (MS Excel) without any manual intervention. Automation is used typically to run macros or queries from Excel to connect to or create or manipulate MS Access database and its structure, to access and manipulate MS Access data and reports, to import data from MS Access to Excel for creating charts and pivot tables and otherwise use the data for calculations and analysis.

ODBC (Open Database Connectivity):

ODBC (Open Database Connectivity) is an interface which enables an application to connect and access a relational database, using the SQL query syntax. An ODBC database is a DBMS (Database Management System) for which there is an appropriate ODBC driver (examples of DBMS include SQL Server, Oracle, AS/400, Foxpro, Microsoft Access). The ODBC Driver is a software that resides between the ODBC Client (which is the front-end application wherein the driver is loaded) and the DBMS (wherein the data is stored for access), and it translates the command into a format that is understood by the DBMS. DAO Object Model uses the Microsoft Jet database engine and is optimized to work Microsoft Access files (.mdb), but ODBC databases can also be accessed with DAO and the Microsoft Jet database engine. A database engine is the underlying software component of a database used to manipulate its data. Jet (Joint Engine Technology) is used by Microsoft Access as its database engine.

OLE DB and ODBC:

OLE DB was intended as a successor to improve on ODBC by providing an enhanced and faster interface for data access. OLE DB is not bound to the SQL language like ODBC and it supports all forms of data sources (ie. relational and non-relational data sources including mainframe and hierarchical databases, e-mail and file systems, text and graphical data, custom business objects, …) whereas ODBC was limited to relational databases. OLE DB was complex to be used directly with Visual Basic and Microsoft’s ADO (ActiveX Data Objects) Object Model was introduced which interfaces with an OLE DB provider and enables an application (viz. Excel) to access and manipulate data from a database (viz. MS Access).

ODBC vs DAO, ADO vs DAO:

When working with ODBC data sources, use ODBC. With ODBC you can access any data source for which there is an appropriate ODBC driver for the database you want to access. Examples of ODBC databases include Oracle, Microsoft SQL Server, Microsoft Visual FoxPro, IBM DB2, Microsoft Access. When working with Microsoft Jet (.mdb) databases, using DAO will be more efficient. Examples of Microsoft Jet databases include Micorsoft Access, Microsoft SQL Server, Paradox. DAO Object Model uses the Microsoft Jet database engine and is optimized to work Microsoft Access files (.mdb), but ODBC databases can also be accessed with DAO and the Microsoft Jet database engine when you want the Jet database engine’s speed and DAO’s extra functionality. DAO precedes ADO and ODBC precedes OLE DB. ADO/OLE DB is recommended for new projects but it might not be worthwhile to convert DAO code to ADO for existing projects.

Add a reference to the DAO Object Library

To use DAO in your VBA project, you must add a reference to the DAO Object Library in Excel (your host application) by clicking Tools-References in VBE, and then choose an appropriate version (mostly, you should choose the highest version number), which is «Microsoft DAO 3.6 Object Library» for Access 2000 onwards.

The DBEngine object

The highest level object in the DAO object model is the DBEngine object, and it contains all objects in the hierarchy of DAO objects. There can only be one DBEngine object and there is no collection of which it is an element of. The DBEngine object has many properties and methods, and contains 2 collections — the Workspaces collection and the Errors collection. You can configure the database engine with properties and methods provided by the DBEngine object. A database engine is the underlying software component of a database used to manipulate its data. You can refer to DBEngine directly without explicitly declaring an object variable of type DBEngine.

Workspace Object & Workspaces Collection

Create a Workspace object to define a user session by name, in which a user performs all database operations by using the Microsoft Access database engine. The Workspace object allows you to open multiple databases or connections in a session, and you can open additional sessions with the Workspace object. A Workspace session starts on creation of a new Workspace object and ends when the Workspace object Close method is used. Multiple sessions (ie. workspace objects) are specifically useful when you want to perform operations as different users or when you want to manage separate and independent operations in each session. All active and unhidden workspace objects are called the Workspaces collection, which is contained in the DBEngine object. In DAO, when you open databases, they automatically exist within the default workspace which is the first workspace in the Workspaces collection. A default workspace, DBEngine.Workspaces(0), is automatically created when a Workspace object is first referred to or used, with the name as «#Default Workspace#», and if security is not enabled with username as «admin» (if security is implemented then username is set to the name of the user who logs on).

You can use the CreateWorkspace method to create a Workspace object. It is not necessary to append a Workspace object to the Wokspaces collection after creating it, and in this case you will need to refer it by the object variable used in the CreateWorkspace method. It will be required to append a Workspace object to the Wokspaces collection after creating it, if you want to refer to it from the Workspaces collection by its ordinal number or Name viz. DBEngine.Workspaces(0) or DBEngine.Workspaces(«WorkspaceObjectName») or DBEngine.Workspaces![WorkspaceObjectName]. All defined DAO Workspace objects appended to the collection comprise the Workspaces collection. There are 2 types of Workspace objects, as defined by WorkspaceTypeEnum Enumeration in the CreateWorkspace method — (i) Microsoft Jet Workspace objects (type — ‘dbUseJet’) which creates a Microsoft Access workspace; and (ii) ODBCDirect workspaces (type — ‘dbUseODBC’) which are  not supported in Microsoft Office Access 2007. In this section we will discuss only the Microsoft Jet Workspace objects.

By default the DBEngine.DefaultUser Property is set to «Admin» and the DBEngine.DefaultPassword Property is set to a zero-length string («») and the default Workspace object’s user and password are defined accordingly. When you start Access or access an Access database with vba, all users automatically log-in with the default name «Admin» and the password of zero-length string («»), but to access a database in a secured system (ie. a secured Access Database) users must provide a username and a password (if a password has been assigned to the user). In a secured system, for the default workspace you set the DefaultUser and DefaultPassword properties (for the DBEngine object), and after the default session has been initialized, additional sessions can be created with user names and passwords. Note that password is case-sensitive but not the username. In this section we do not go into further details of accessing a secured Microsoft Access database.

DBEngine.CreateWorkspace Method

Use the DBEngine.CreateWorkspace Method to create a new Workspace object. Syntax: DBEngineObject.CreateWorkspace(Name, UserName, Password, UseType). All arguments, except UseType, are mandatory. In the Name argument, specify a unique Workspace name for a session. In the UserName argument, specify the name of the user for identification. In the Password argument, you are required to enter a password for the Workspace object with a maximum of 20 characters. The UseType argument specifies one of the WorkspaceTypeEnum values: (i) dbUseJet — (Microsoft Jet Workspace objects) which creates a Microsoft Access workspace, and is also the default; and (ii) dbUseODBC — for ODBCDirect workspaces which are  not supported in Microsoft Office Access 2007.

In DAO, when you open databases, they automatically exist within the default workspace which is the first workspace in the Workspaces collection. You need to use the DBEngine.CreateWorkspace Method only to create a second workspace which is seldom required.

Example 1: DAO WorkSpace Object & Workspaces Collection.

1. Create a new Workspace object, using the CreateWorkspace method, and append to the Workspaces collection.
2. Access properties of all workspace objects (ie. default workspace and the newly created workspace).

Sub AccessDAO_CreateWorkspace_1()
‘Create a new Workspace object, using the CreateWorkspace method, and append to the Workspaces collection.

‘Access properties of all workspace objects (ie. default workspace and the newly created workspace).

‘workspace name (returns «#Default Workspace#» & «newWS»):

MsgBox «Workspace Name: » & wrkSpace.Name

‘username property setting:

MsgBox wrkSpace.UserName

‘properties of workspace object:

For Each prpWrkSpace In wrkSpace.Properties

MsgBox «Property Name: » & prpWrkSpace.Name

Next prpWrkSpace

End Sub

DAO Workspace Object Methods

DAO Workspace Object Methods: The Close Method is used to close an open Workspace. CreateDatabase method is used to create a new database and the OpenDatabase method is used to open an existing database. To manage transaction processing during a session (ie. when a series of database changes made in a session are treated as one unit), you have three transaction methods of BeginTrans, CommitTrans and Rollback. The OpenConnection Method, available only in an ODBCDirect workspace, is used to open a connection to an ODBC data source. Note that Microsoft Office Access 2007 does not support ODBCDirect workspaces.

DAO Databases

DBEngine.OpenDatabase Method

Use the DBEngine.OpenDatabase Method to open a Database, as specified by its name/path. A reference to the Database object variable (to which the database is assigned) is returned by this method, and the database is not actually opened in the Microsoft Access window. If you open a database object without specifying a workspace, it will exist within the default workspace: DBEngine.Workspaces(0). Syntax: DBEngineObject.OpenDatabase(Name, Options, ReadOnly, Connect). Name argument is mandatory while all other arguments are optional. In the Name argument you will specify the database file name and full path, which you want to open. In the Options argument, you can specify False which is the Default and opens the database in shared mode while specifying True opens the database in exclusive mode. In the ReadOnly argument specifying False (default) will open the database with read-write access and specifying True will open in read-only. Connect argument is used to specify connection information (ex. password).

DAO Workspace.OpenDatabase Method

Use the DAO Workspace.OpenDatabase Method to open a Database, as specified by its name/path, in the specified Workspace object. A reference to the Database object variable (to which the database is assigned) is returned by this method, and the database is not actually opened in the Microsoft Access window. Syntax: WorkspaceObject.OpenDatabase(Name, Options, ReadOnly, Connect). The arguments are similar to as in the DBEngine.OpenDatabase Method, explained above.

DAO DBEngine.CreateDatabase Method

Use the DAO DBEngine.CreateDatabase Method to create, open and save a new Database. A reference to the Database object variable (to which the new database is assigned) is returned by this method. Note that this method creates a new empty database, which you will need to structure and enter content thereafter. If you create a database object without specifying a workspace, it will exist within the default workspace: DBEngine.Workspaces(0). Syntax:  DBEngineObject.CreateDatabase(Name, Locale, Option). Name and Locale arguments are mandatory. In the Name argument (max 255 characters) you will specify the file name and full path of the database which is being created. The Locale argument specifies a collating order for the database (this is equated with the Database.CollatingOrder Property which specifies the database sort order sequence) ie. the character set to be used to determine how database values will be sorted. Specifying the constant «dbLangGeneral» for this argument means creating a database which will support sorting for «English, German, French, Portuguese, Italian, and Modern Spanish». A password for the new Database can also be created in concatenation with the constant specified in the Locale argument viz. dbLangGeneral & «;pwd=123», where password is «123». The Option argument specifies a constant to determine the version for the data format and if the database should be encrypted, and not specifying a constant will create an un-encrypted database.

DAO Workspace.CreateDatabase Method

Use the DAO Workspace.CreateDatabase Method to create, open and save a new Database. A reference to the Database object variable (to which the new database is assigned) is returned by this method. Note that this method creates a new empty database, which you will need to structure and enter content thereafter. This method creates a new Database and opens it in the specified workspace object. Syntax:  Workspace.CreateDatabase(Name, Locale, Option). The arguments are similar to as in the DBEngine.CreateDatabase Method, explained above.

Example 2: Open an existing Database, Create a new Database.

1. Open an existing Database using the DAO OpenDatabase Method.
2. Create a new Database using the DAO CreateDatabase Method.
3. Return Databases and enumerate their properties in a Workspace.

MsgBox daoDBS.Name

For Each prpDB In daoDBS.Properties

MsgBox «Property Name: » & prpDB.Name

Next prpDB

MsgBox daoDBS.Name

For Each prpDB In daoDBS.Properties

MsgBox «Property Name: » & prpDB.Name

Next prpDB

End Sub

Return a Reference to the Current Database — CurrentDb Method

Use the CurrentDb Method to return a reference to the database which is currently open in the Microsoft Access window, from vba code. The method returns a database object, without the need to specfy the database name. You can use other DAO objects with the database object variable returned by this method. A reference to the current database is provided by the first member of the Databases collection. The reference pointed to the current database by using the syntax DBEngine(0)(0) can also be used but this syntax refers to the open copy of the current database, whereas with the CurrentDb method you can create ‘multiple database object variables’ referring to the current database because this method creates a new instance of the current database making it amenable for multi users. However, it is much slower to use CurrentDb than using DBEngine(0)(0). Note that another Database can be opened and worked upon simultaneously, using the OpenDatabase method, while the current database is already open in the Microsoft Access window.

Example 3: CurrentDb Method — return a reference to the currently open database.

For Each fld In daoTblDef.Fields

MsgBox fld.Name

Next fld

Set recSet = Nothing

End Sub

Tables of a DAO Database

TableDef Object and TableDefs collection

A TableDef object, with its properties and methods, is used to manipulate a table definition. With a TableDef object you can: create a new table (Database.CreateTableDef Method); create or add a new Field in a table (TableDef.CreateField Method); create a new Index (TableDef.CreateIndex Method); create a new Recordset and append it to the Recordsets collection (TableDef.OpenRecordset Method); update a linked table’s connection information (TableDef.RefreshLink Method); set or return information about a linked table (TableDef.Connect Property); set or return the name of a linked table (ableDef.SourceTableName Property); set or return validation value/rule for a field’s data (TableDef.ValidationRule Property); set or return the text message displayed when the field value does not conform to the ValidationRule (TableDef.ValidationText Property); and so on.

All stored TableDef objects in a database are referred to as the TableDefs collection. You create a new TableDef object using the Database.CreateTableDef Method. It is required to append a TableDef object to the TableDefs collection after creating it, using the DAO TableDefs.Append Method. You can refer to a TableDef object in the TableDefs collection by its ordinal number or Name viz. TableDefs(0) or TableDefs(«TableDefObjectName») or TableDefs![TableDefObjectName].

Database.CreateTableDef Method

Use the Database.CreateTableDef Method to create a new TableDef object. Syntax: DatabaseObject.CreateTableDef(Name, Attributes, SourceTableName, Connect). All arguments are optional to specify. The Name argument sets the name of the TableDef object, which can be a maximum of 64 characters. The Attributes argument sets a value indicating characteristic(s) of the TableDef object. The Attributes Property is read/write for a TableDef object till it is appended to its collection. The SourceTableName argument specifies the name of a linked or the base table that is the original data source in an external database. The Connect argument is a String value, which provides information of a TableDef object’s linked table or an open database source, consisting of a database type specifier and a database path.

Note that it is required to define one Field atleast before you can append a TableDef object to the TableDefs collection. Use the TableDefs.Delete Method to delete a TableDef object from the TableDefs collection.

Fields / Columns of a Table

A Field object corresponds to a column of data of similar data type and properties. The Index, QueryDef, Relation and TableDef objects all have a Fields collection, which represents all stored Field objects as specified in the respective object. The Recordset object also has a Fields collection, which represents all stored Field objects in a record or a row of data. A field object has its own properties & methods by which it is manipulated.

Create a new Field

TableDef.CreateField Method 

Use the TableDef.CreateField Method to create a new Field object. Syntax: TableDefObject.CreateField(Name, Type, Size). All arguments are optional to specify. The Name argument specifies a name for the new Field. The Type argument sets the data type of the Field, as indicated by a constant. The Size argument determines the maximum size of a Field. For a Field with character data (except Memo), size determines the maximum number of characters; for numeric fields, it is the maximum size in bytes (of storage). Text fields can be set upto a maximum of 255 characters for a Microsoft Access database, whereas for non-Text fields the size is automatically determined by their Type property. Not specifying the Size will default the Field size to as permissible by the database. For Memo or Long Binary Fields use the Field.FieldSize Property to determine the size in the number of bytes used in the database, whereas use the Size property for all other Field data types.

You can use the CreateField method to add a new field to an Index or Relation object. To add a field to an Index object, use the DAO Index.CreateField Method, Syntax: IndexObject.CreateField(Name, Type, Size). The type and size arguments are not supported for an Index object, and are ignored in this case. To add a field to a Relation object, use the DAO Relation.CreateField Method, Syntax: RelationObject.CreateField(Name, Type, Size). The type and size arguments are not supported for a Relation object, and are ignored in this case.

Fields Collection Properties & Methods

Count the number of Fields

The Count property of the fields collection determines the number of fields in a collection, wherein numbering for members of a collection begins with zero. If you have seven fields in a Recordset, using RecordsetObject.Fields.count will return 7, and RecordsetObject.Fields(0) will return the value of the first field [OrdinalPosition of the first field is 0].

Access Fields by their ordinal position or Name property

You can Access Fields by their ordinal position or Name property viz. Recordset.Fields.(Name/OrdinalPosition). Recordset.Fields(0).Name returns the Name of the first field, and Recordset.Fields(0).Value returns the content in the first field. The Value property of the Field object is its Default property viz Recordset.Fields(0) is the same as Recordset.Fields(0).Value and will return the first fields’s value.

Examples: To reference a field named «FirstName», which is the second field in the table, you can use any of the following:-

RecordsetObject.Fields(«FirstName»)

RecordsetObject.Fields(1)

RecordsetObject![FirstName]

DAO Fields.Append Method

To add or append a new field to the Fields Collection of a TableDef or an Index object, use the DAO Fields.Append Method. To add a field to a table, use the Syntax: TableDefObject.Append(FieldObject). To add a field to an Index, use the Syntax: IndexObject.Append(FieldObject). The FieldObject argument mentions the Field Object variable which is being appended and is necessary to specify.

DAO Fields.Delete Method

To delete a field from the Fields Collection, use the DAO Fields.Delete Method. To delete a field from a table, use the Syntax: TableDefObject.Fields.Delete(Name). The Name argument mentions the name of the Field which is being deleted and is necessary to specify. Note that once an index referencing a field has been created, that Field cannot be deleted from a Fields collection of a TableDef object.

DAO Fields.Refresh Method

The relative position of a Field object within the Fields collection is usually the order in which the field has been appended in the collection, the first appended field at first position will have an OrdinalPosition of 0 (zero), the second appended field at second position will have an OrdinalPosition of 1, and so on, and this position can be changed (or returned) by using the DAO Field.OrdinalPosition Property. A change in the ordinal position of a Field may not change the order of the Fields in the collection unless the DAO Fields. Refresh Method is used. The Refresh method is particularly required to be used in a multi-user environment wherein different users might be making changes in the database, in which case only those objects are contained when you have referred to the collection initially without reflecting any subsequent changes made by other users, and the collection will get updated only on using the Refresh method.

Field Object Properties

Field properties are used to determine or return the name, size, type and characteristics of a Field. Some of these properties are elaborated below.

DAO Field.Name Property

Use the DAO Field.Name Property to set or return a Field’s name. It is a String value not exceeding 64 characters. The property is read-only after the Field object is appended to the Fields collection, before which it is read/write.

DAO Field.Value Property

Use the Field.Value Property to return, enter or edit the data in a Field. This is the default property of a Field object viz. you can refer to a field object without specifying the value property. For example, entering «Lisa» in the field named «FirstName» can be done either as RecordSetObject.Fields(«FirstName») = «Lisa» or as RecordSetObject.Fields(«FirstName»).Value = «Lisa».

DAO Field.OrdinalPosition Property

The relative position of a Field object within the Fields collection is usually the order in which the field has been appended in the collection, the first appended field at first position will have an OrdinalPosition of 0 (zero), the second appended field at second position will have an OrdinalPosition of 1, and so on, and this position can be changed (or returned) by using the DAO Field.OrdinalPosition Property. Note that this property uses «relative postion» so that if you have 3 fields and you change the OrdinalPosition property of these to 10, 12 & 15, then the field with OrdinalPosition value of 12 will be returned in an order relative to the others, ie. between the fields whose values have been set as 10 and 15.

The property is read-write for a Field object before it is appended to a Fields collection. After a Field object is appended, for Fields contained within a TableDef object it is read-write, and for fields contained within Recordset or QueryDef objects it is read-only, but the property is not supported for fields contained within Index & Relation objects.

DAO Field.Size Property

The Field.Size Property determines the maximum size of a Field. For a Field with character data (except Memo), size determines the maximum number of characters; for numeric fields, it is the maximum size in bytes (of storage). For Text fields you must set the Size property which can be set upto a maximum of 255 characters for a Microsoft Access database, whereas for non-Text fields the size is automatically determined by their Type property. Not specifying the Size will default the Field size to as permissible by the database. For Memo or Long Binary Fields use the Field.FieldSize Property to determine the size in the number of bytes used in the database, whereas use the Size property for all other Field data types.

The property is read-write for a Field object before it is appended to a Fields collection. After a Field object is appended, the property is supported for Fields contained within a TableDef object, Recordset object or QueryDef object, wherein it is read-only, but the property is not supported for fields contained within Index & Relation objects. 

DAO Field.Type Property

Use the Type property to set or return the operational or data type of a Field. The value returned by this property is a constant which indicates the data type of a field. The property is read-only after the Field object is appended to the Fields collection or to any object, before which it is read/write.

Examples of data type constants that are supported by DAO, for the Type property, include:

dbBoolean (Boolean Value — Yes/No); dbChar (Char); dbCurrency (Currency); dbDate (Date); dbDouble (Double); dbGUID (GUID); dbInteger (Integer); dbBigInt (Big Integer); dbSingle (Single); dbLong (Long); dbMemo (Memo); dbText (Text); ….

DAO Field.Attributes Property

Use the DAO Field.Attributes Property to set (or return) the Field characteristics. The Field characteristic(s) is specified by a value or constant, which can be: dbAutoIncrField (to automatically increment the Field value to a unique Long integer); dbDescending (to sort Field values in a descending order — default sort order for a Field is Ascending if this attribute is not specified — this attribute is applicable only to an index field ie. to Fields collection of an Index); dbFixedField (dbFixedField specifies that the field has a fixed size —  numeric fields have a Fixed field size by default — maps to ADO column attribute adColFixed); dbVariableField (valid only  for text fields, it specifies a Variable Field size ie. the Text data type Field can store variable text lengths); dbUpdatableField (when the Field value can be updated or changed); dbHyperlinkField (hyperlink field, valid only for Memo field types); dbSystemField (these fields cannot be deleted).

To create an auto-increment field, set data type of field to Long and set Attributes property to dbAutoIncrField. An auto-increment field (also referred to as AutoNumber field) by default starts at 1 and increments sequentially and can be used aptly as a primary key field to automatically insert unique numbers in a field.

Set multiple attributes — sum the respective constants (using the plus «+» sign) to set multiple attributes, wherein any non-meaningful values get ignored without giving an error.

This property is read/write for a field before being appended to a collection. For a Field object after it is appended to a collection: for Fields contained within a TableDef object, the property is read/write; for Fields contained within an Index object, this property remains read-write until the TableDef object which contains the Index object is appended to a Database and then read-only thereafter; for Fields contained within a Recordset object or QueryDef object, the property is read-only; for Fields contained within a Relation object this property is not supported.

DAO Field.DefaultValue Property

Use the Field.DefaultValue Property to specify the default value to be entered in a Field automatically on creation of a new record. A text or an expression of String data type upto a maximum of 255 characters, can be specified as the default value. For AutoNumber and Long Binary fields, this property is not applicable.

The property is read-write for a Field object before it is appended to a Fields collection. After a Field object is appended, for Fields contained within a TableDef object it is read-write, and for fields contained within Recordset or QueryDef objects it is read-only, but the property is not supported for fields contained within Index & Relation objects.

DAO Field.Required Property

The Field.Required Property determines whether a field can accept null values. Setting the Property to False will allow null values in the field. Between an Index object and a Field object, set the Required property for the Field object because its validation for the Field object precedes that of an Index object.

The property is read-write for a Field object before it is appended to a Fields collection. After a Field object is appended, for Fields contained within a TableDef object it is read-write, and for fields contained within Recordset or QueryDef objects it is read-only, but the property is not supported for fields contained within Index & Relation objects.

DAO Field.AllowZeroLength Property

Setting the Field.AllowZeroLength Property to True will allow value for Text or Memo data type Fields to be set to an empty or zero-length string («»). Zero Length string vs Null value: Note that in Access when you specify a Zero Length string it means that you actually specify a value, and when you set the Required porperty to be True it means that the Field can have a Null value which means that NO value needs to be entered — for the user there is no visible difference between the two.

The property is read-write for a Field object before it is appended to a Fields collection. After a Field object is appended, for Fields contained within a TableDef object it is read-write, and for fields contained within Recordset or QueryDef objects it is read-only, but the property is not supported for fields contained within Index & Relation objects.

DAO Field.ValidationRule Property

Use the Field.ValidationRule Property to validate a field’s data with a specified rule or condition. The property specifies a string value as a comparison like in a WHERE clause (as used in SQL statements) but does not use the WHERE word. If the field’s value does not conform to the specified rule or condition, the error message (a string value) as specified by the ValidationText property gets displayed. Only databases using the Microsoft Access database engine support validation.

The property is read-write for a Field object before it is appended to a Fields collection. After a Field object is appended, for Fields contained within a TableDef object it is read-write, and for fields contained within Recordset or QueryDef objects it is read-only, but the property is not supported for fields contained within Index & Relation objects.

DAO Field.ValidationText Property

Validation Text specifies the error message (a string value) which gets displayed if the field’s value does not conform to the specified rule or condition specified by the ValidationRule property.

The property is read-write for a Field object before it is appended to a Fields collection. After a Field object is appended, for Fields contained within a TableDef object it is read-write, and for fields contained within Recordset or QueryDef objects it is read-only, but the property is not supported for fields contained within Index & Relation objects.

Example 4a: Create Tables and Fields in a DAO Database.

Refer Image 4a as mentioned in the code.

1. Create a New Database;
2. Create & Append Tables (ie. TableDef objects);
3. Create & Append Fields;
4. Enumerate Tables in the Database and their Properties;
5. Enumerate Fields in a Table;
6. Delete Fields & Tables;

‘set the string variable to the new Database:

Set daoTD2 = daoDB.CreateTableDef(«Performance»)

‘Before you append the TableDef object to the TableDefs collection, you will create Fields and append them to the new TableDef object (Table named «SalesManager») created above:

With daoTD1

.Fields.Append daoFld

End With

‘Before you append the TableDef object to the TableDefs collection, you will create Fields and append them to the new TableDef object (Table named «Performance») created above:

With daoTD2

.Fields.Append .CreateField(«FirstName», dbText)

End With

‘Enumerate Tables in the database and their properties:
For Each daoTD In daoDB.TableDefs

‘Use the Attributes property to ignore System and Hidden Tables. The Attributes argument returns or sets a value indicating characteristic(s) of the TableDef object. Note, that to check a specific attribute we have used the logical AND operator for comparison of: (i) the TableDef Attributes property and the dbSystemObject constant; and (ii) the TableDef Attributes property and the dbHiddenObject constant. You can alternatively do an equivalency test using numerical values of the constants.
If ((daoTD.Attributes And dbSystemObject) Or (daoTD.Attributes And dbHiddenObject)) Then
Else

For Each daoPrp In daoTD.Properties

MsgBox «Table Name: » & daoTD.Name & » —   Property Name: » & daoPrp.Name & «,   Property Type: » & daoPrp.Type & «,   Property Value: » & daoPrp.Value

Next

‘If daoTD.Attributes >= 0 And daoTD.Attributes <> 1 Then

‘MsgBox «Table Name: » & daoTD.Name

‘End If

Next

‘Enumerate Fields and return their name, type & size in the Table named «SalesManager»:

For Each daoFld In daoTD1.Fields

MsgBox daoFld.Name & «, » & daoFld.Type & «, » & daoFld.Size

Next

Set daoPrp = Nothing

End Sub

Recordset & Records of a DAO Database Table

After connecting to a database, you can manipulate its data. In Microsoft Access, Recordset objects are used to access and manipulate data in a database. A Recordset object represents a set of records in a database table, or a set of records returned from running a query. Both DAO and ADO libraries have a Recordset object, though the methods, properties, and options of the respective object is different. A Record object is one row of data in a Recordset. A Recordset object has a Fields collection which contains all the Field objects, where each Field object represents a column in the Recordset. In other words, each record represents a row of data and contains many fields, and each field corresponds to a column in the database table.

In your VBA code, you should ideally precede the object name by its program ID (ProgID) prefix, which in ADO is «ADODB» and in DAO is «DAO». Many objects, for example the Recordset object, have similar names in both DAO and ADO and it is advisable to have explicit references in your project. This becomes a must if you have included references to both the DAO and ADO libraries in your VBA project, else the object library mentioned first in the References list will prevail, resulting in confusion in the vba code.

While instantiating the Recordset object, you should use:

Dim daoRecSet As DAO.Recordset

Dim adoRecSet As ADODB.Recordset

instead of:

Dim RecSet As Recordset

DAO Recordset Types

There are five types of Recordsets:

1. A Table-type recordset is based on a Table and not on a query. A Table-type recordset is created only when working with a single non-linked table. Valid for Microsoft Access Jet workspaces only. You can use the Seek method (but not the Find Method) to search through this recordset (using a Table index), which is faster than using the Find method.

2. A Dynaset-Type recordset results from a query. The set of records can contain fields from one or more underlying tables or any linked table (ie. any table linked to the Access Database). The recordset gets dynamically updated and reflects any change made to the underlying records. After the recordset has been created it does not add any new record satisfying the criteria. This recordset type supports the Find method (but not the Seek method) to search through the recordset, which is however slower than the Seek method.

3. A Snapshot-type recordset shows the data as at the time when a snapshot is taken ie. when a recordset is created. The set of records can contain fields from one or more underlying tables or any linked table. This recordset type is a static copy of the records and does not get dynamically updated and does not reflect any change made to the underlying records. If a field value is changed in a record, it will not be updated dynamically like it gets done in a Dynaset-Type recordset and you will need to refresh the recordset to update. This recordset type is used to read data and searching through this recordset is very fast. This recordset type supports the Find method to search through the recordset.

4. A Forward-only-type recordset is identical to a snapshot-type wherein only scroll forward through records is possible.

5. A Dynamic-type recordset results from a query from one or more underlying tables. In this recordset you can add, change or delete records from a row-returning query. This recordset is similar to the Dynaset-Type except that after running a query the matching records added, deleted or edited in the underlying tables by other users also get automatically reflected in the recordset of this type. Valid for ODBCDirect workspaces only.

All active recordsets of a database are contained in the Recordsets collection, wherein a recordset gets appended to the collection when it is opened and gets removed from the collection when it is closed (using the Close method). Each recordset object contains a collection of the fields and a collection of the indexes in the underlying table.

DAO Recordset.Type Property

Use the Recordset.Type Property to set or return the type of Recordset, using the RecordsetTypeEnum constants or values. There are five settings: dbOpenTable (value-1, Table-type, for Microsoft Access workspaces only); dbOpenDynaset (value-2, Dynaset-type); dbOpenSnapshot (value-4, Snapshot-type); dbOpenForwardOnly (value-8, Forward-only type); dbOpenDynamic (value-16, Dynamic-type, for ODBCDirect workspaces only).

Create a new Recordset object

Create a Recordset object and append it to the Recordsets collection, using the OpenRecordset method. You can use the OpenRecordset method to open a Recordset that is based on a Table, SQL statement, stored or parameter query as detailed below. Arguments have the same meaning across the OpenRecordset methods.

DAO Database.OpenRecordset Method. Syntax: DatabaseObject.OpenRecordset(Name, Type, Options, LockEdit). In this method you pass the Table name to the method and use the Set operator to return the recordset.

Only the Name argument is mandatory to specify while other arguments are optional. The Name argument specifies the source of records and can be the name of a table or a query, or it can be an SQL statement. In the Type argument, specify one of the five types for the recordset by using the constants: dbOpenTable (Table-type); dbOpenDynaset (Dynaset-type); dbOpenSnapshot (Snapshot-type); dbOpenForwardOnly (Forward-only type); dbOpenDynamic (Dynamic-type). A Recordset created in a Microsoft Access local table without specifying the Type will default to Table-type. Executing the OpenRecordset method on a linked table or query, without specifying the Type, will default to Dynaset-type. In the Options argument you can specify one of the many constants representing the recordset’s characteristics viz. specifying dbReadOnly opens a recordset as read-only, and so on. The LockEdit argument specifies a constant which determines the type of record locking used when a recordset is opened.

DAO TableDef.OpenRecordset Method. Syntax: TableDefObject.OpenRecordset(Type, Options). In this method you first get a reference to the Table (TableDefObject) and then use the Set operator to return the recordset.

DAO Recordset.OpenRecordset Method. Syntax: RecordsetObject.OpenRecordset(Type, Options). In this method you first get a reference to a Recordset Object and then use the Set operator. Refer Example 7 wherein this method is used to Filter Records.

Creating a Recordset, based on a stored query or a parameter query, using the QueryDef.OpenRecordset Method. For details on this method, refer section «Create and Exceute a Query».

Create a new record in a Database Table — use the AddNew & Update methods

DAO Recordset.AddNew method

Create a new record for a Recordset object, using the Recordset.AddNew method. Syntax: RecordsetObject.AddNew. When you use this method, the field’s value is set to its default value and in the absence of a default value specification, it is set to Null. Ensure that after adding a new record using the AddNew method or after making any changes in a record using the Edit method, you must save the record and/or any changes to it by using the Update method BEFORE you perform any operation like move to another record or use the Edit or AddNew method again or close the recordset or set bookmark property for another record.

In DAO, after using the Update method, the current record will be the record which had focus before the AddNew method. Using the LastModified property (for a DAO recordset) returns a Bookmark pointing to the most recent added / modified record and setting the Bookmark property to this bookmark will make the new record as the current record.

When you add a record to a dynaset-type Recordset, using the AddNew method, the new record will appear at the end of the recordset disregrading the recordset’s sorting if any. In this case you can re-create the recordset or use the ReQuery method to have the new record appear in its sorted position. When a record is added to a table-type Recordset, the new record appears in accordance with the recordset’s index and in the absence of an index the new record will appear at the end of the recordset.

DAO Recordset.Update Method

Ensure that after adding a new record using the AddNew method or after making any changes in a record using the Edit method, you must save the record and/or any changes to it by using the Recordset.Update Method BEFORE you perform any operation like move to another record or use the Edit or AddNew method again or close the recordset or set bookmark property for another record. Syntax: RecordsetObject .Update(UpdateType, Force). Both arguments of UpdateType & Force are optional.

Recordset.LastModified Property

In Table-type or Dynaset-Type recordsets, a bookmark of the record which has most recently been added or changed, is returned by the Recordset.LastModified Property. Use this property to bookmark and move to the record which has last been added or modified. Syntax: RecordsetObject.LastModified. Refer Example 4b for using this property.

Recordset.Bookmark Property

Use the Recordset.Bookmark Property to uniquely identify the current record by setting or returning a bookmark. You can create any number of bookmarks in a recordset, by saving each bookmark and assigning its value to a variable and then return to that record by setting the Recordset’s Bookmark property to the variable. Refer Example 4b for using this property.

Edit Records in a Recordset

Use the DAO Recordset.Edit Method to make changes to fields of the current record in a Recordset object. Ensure that after making any changes in a record using the Edit method, you must save the changes to it by using the Update method. After editing the record, the current record to which changes are made remains current ie. the record with focus. Syntax: RecordsetObject.Edit.

Moving between Records in a Recordset

DAO Recordset.Move Method. Syntax: RecordsetObject.Move(Rows, StartBookmark). This method moves the position of the current record as per the specified number of rows (Rows argument) starting from a bookmarked record specified by the StartBookmark argument or from the current record if this argument is omitted. It is necessary to specify the Rows argument, and if this is more than 0 the current record moves forward towards end of recordset, and if less than 0 then the current record moves backwards. You can use this method with rows argument set to 0, to retrieve the current record’s underlying data.

MoveFirst, MoveLast, MoveNext, and MovePrevious Methods (DAO): MoveFirst method moves the current record to the first record. Remember that on opening a recordset, the first record is the current record. Using the MoveLast method moves the current record to the last record in the recordset. MoveNext method moves the current record one position forward and MovePrevious moves the current record one position backward. Note that the MoveFirst, MoveLast, and MovePrevious methods cannot be used on a Forward-only-type recordset. Syntax: RecordsetObject.MoveFirst, RecordsetObject.MoveLast, RecordsetObject.MoveNext, RecordsetObject.MovePrevious.

EOF Property (DAO) indicates whether the current record position is after the last record in the set of records, wherein its value will be TRUE. BOF Property (DAO) indicates whether the current record position is before the first record in the set of records, wherein its value will be TRUE. Both properties return a Boolean value and are used to determine if the current record is outside the limits of the Recordset object. There will be no current record if either the EOF Property or BOF Property is True, and if both properties are True on opening a recordset it will indicate that there are no records. Opening a Recordset having atleast one record makes the first record as the current record and in this case both the EOF Property and BOF Property will be False. Syntax: RecordsetObject .EOF, RecordsetObject .BOF.

Count the number of Records in a Recordset

Use the DAO Recordset.RecordCount Property to: (i) count the number of records which have been acceessed in a Dynaset-Type or Snapshot-type or Forward-only-type recordset, and after the last record is accessed (ie. after the recordset is populated) RecordCount indicates the total number of records contained in the recordset; or (ii) count the total number of records in a table-type Recordset or in a TableDef object, wherein RecordCount always returns the correct number. To forcibly access the last record in a Dynaset-Type or Snapshot-type or Forward-only-type recordset, use the Recordset.MoveLast method. Syntax: RecordsetObject.RecordCount.

Close DAO objects, using the Close Method

You should close an open Recordset by using the DAO Recordset.Close Method, which will free any associated system resources. Similarly, close an open Workspace object using the Workspace.Close Method and close an open Database using the Database.Close Method. Closing an object is not enough to remove it from memory, for which you need to set the object variable to Nothing, after closing the object.

To close a Recordset: RecordsetObject.Close

To destroy the Recordset variable: Set RecordsetObject = Nothing

Example 4b: Add / Edit Records and Enter Data, in Tables.

Refer Image 4b as mentioned in the code.

1. Add new records to a table using the AddNew method;
2. Edit records using the Edit method;
3. Use the Recordset.Bookmark Property to identify the current record;
4. Use Recordset.LastModified Property pointing to the most recent added / modified record.

.AddNew
‘you need not enter a value for the auto-incrementing field of «EmployeeId»; the start value is 1. In DAO you cannot set the Seed of the auto-number, however you can start at a specific value in a new table by entering the specific value for the first record of an AutoNumber field and subsequent records will increment from this specific start value.
.Fields(«EmployeeId») = 55
.Fields(«FirstName») = «Lisa»
.Fields(«SurName») = «Randall»
‘enter a date/time value between # and #, or within double-quotes:
.Fields(«JoinDate») = «08/11/2012»
.Fields(«Sales») = «22456»
.Fields(«NewJoinee?») = True
‘for a hyperlink field, use both # and double-quotes:
.Fields(«WebProfile») = «#http://www.google.com#»
‘will save only after Update method is run:

.AddNew
‘note that «JoinDate» field is omitted, hence its default value will be entered
.Fields(«FirstName») = «Tracy» & » » & «Von»
.Fields(«SurName») = «Murray»
.Fields(«Sales») = «41098»
.Fields(«NewJoinee?») = False
.Fields(«WebProfile») = «#http://www.yahoo.com#»
.Update
‘second record — save position of current record:
.Bookmark = .LastModified

.AddNew
.Fields(«FirstName») = «John»
.Fields(«SurName») = «Mason»
.Fields(«JoinDate») = #9/2/2012#
.Fields(«Sales») = «31478»
.Fields(«NewJoinee?») = True
.Fields(«WebProfile») = «#http://www.msn.com#»

‘In DAO, after the Update, the current record will be the record which had focus before the AddNew. Using the LastModified property (for a DAO recordset — it does not work with an ADO recordset) returns a Bookmark pointing to the most recent added / modified record. This makes the new record as the current record.

.Bookmark = .LastModified

‘edit the new record, using the Edit method (of the Recordset object):
With recSet

‘Recordset.Edit Method is valid for a DAO recordset, it does not work with an ADO recordset:
.Edit
.Fields(«FirstName») = «Julia»
.Fields(«SurName») = «Willis»
‘will save only after Update method is run:

.Update

End Sub

Example 5a: Open Recordset, Enumerate Recordset, Recordset Properties, Navigate through Records.

1. OpenRecordset method of the Database object — Open Recordset based on a Table; Open Recordset based on a SQL statement.
2. OpenRecordset method of the TableDef object — Open Recordset based on a Table.
3. Enumerate the Recordset; List all valid properties of Recordset.
4. Use the MoveFirst and MoveNext methods to navigate through records, together with EOF Property.

‘return the first field (name & value) of each record of the Recordset:

‘while moving forward within a recordset, use EOF so as not to cross the last record. EOF Property indicates that the current record position is after the last record in the set of records.

Do While Not recSet.EOF

MsgBox recSet.Fields(0).Name & » — » & recSet.Fields(0).Value

‘MoveNext method moves the current record one position forward.

recSet.MoveNext

recSet.Close

‘navigate through records in a recordset:
With recSet

‘MoveFirst method moves the current record to the first record.
.MoveFirst
Do While Not .EOF

MsgBox «Record No. » & n
For i = 0 To fieldsCount — 1

MsgBox .Fields(i).Name & » — » & .Fields(i).Value

Next i

.MoveNext

n = n + 1

Loop

recSet.Close

‘List all fields of each record of the Recordset:
Do While Not recSet.EOF

For Each daoFld In recSet.Fields

MsgBox daoFld.Name & » — » & daoFld.Value

Next daoFld

recSet.MoveNext

‘List all valid properties of the Recordset object:
For Each daoPrp In recSet.Properties

‘skip invalid values with resume next statement

On Error Resume Next

MsgBox «Property Name: » & daoPrp.Name & «;     Property Value: » & daoPrp.Value

End Sub

Example 5b: Count the number of Records in a Recordset — DAO Recordset.RecordCount Property.

Refer Image 5 as mentioned in the code.

End Sub

Example 6: Find Method (FindFirst & FindNext) in a Dynaset or Snapshot-type recordset; Edit / Delete Records.

Refer Images 6a, 6b & 6c as mentioned in the code.

1. Locate records matching specified criteria using the FindFirst and FindNext methods in a dynaset or snapshot-type recordset;
2. Edit a record using the Edit method;
3. Delete a record using the Delete method.

‘if a record with matching criteria is found:
If recSet.NoMatch = False Then

‘the NoMatch property is set to True, if no matched record is found:

Do While Not recSet.NoMatch

‘return record with matching criteria: returns Murray, Mason & Davis: refer Image 6a:

MsgBox recSet.Fields(«SurName»)

‘locate next record with matching criteria:

recSet.FindNext «SurName LIKE ‘*A*'»

Loop

Else

MsgBox «No Matching Record Found!»

‘the NoMatch property is set to True, if no matched record is found:
If Not recSet.NoMatch Then

‘modifying a DAO recordset — edit a record in a table, using the Edit method (of the Recordset object):

With recSet

.Edit

.Fields(«FirstName») = «James»

.Fields(«SurName») = «Bond»
‘will save only after Update method is run:

.Update

‘Using the LastModified property returns a Bookmark pointing to the most recent added / modified record. This makes the new record as the current record.

.Bookmark = .LastModified

End With

Else

MsgBox «No Matching Record Found!»

‘modifying a DAO recordset — delete a record in a table, using the Delete method (of the Recordset object):

‘record with EmployeeId 56 is deleted, refer Image 6c:

If recSet.NoMatch = False Then

recSet.Delete

Else

MsgBox «Record Not Found»

End If
 

‘go to the Last Record, then go back one record:

With recSet

.MoveLast

.Move -1

‘returns Jim, refer Image 6c:

MsgBox recSet.Fields(«FirstName»)

End Sub

Example 7: Use the DAO Recordset.Filter Property to Filter Records (applicable to dynaset–type, snapshot–type, or forward–only–type Recordsets).

Refer Images 7a & 7b, as mentioned in the code.

Sub AccessDAO_RecordsetFilter_7()
‘Filter Records: Use the DAO Recordset.Filter Property to determine inclusion of records in a Recordset opened thereafter. A Filter can be applied to dynaset–type, snapshot–type, or forward–only–type Recordsets.

‘To use DAO in your Excel VBA project, you must add a reference to the DAO Object Library in Excel (your host application) by clicking Tools-References in VBE.

‘set values of all records in NewJoinee? field (Boolean) to False:
‘refer Image 7a to view the SalesManager Table in MS Access file «SalesReport.accdb», after running below code.
Set recSet = daoDB.OpenRecordset(«SalesManager»)

Do While Not recSet.EOF

recSet.Edit

recSet.Fields(«NewJoinee?»).Value = False

recSet.Update

recSet.MoveNext

‘return the EmployeeId & JoinDate fields of each record in the filtered Recordset:

‘refer Image 7b to view the SalesManager Table, after running below code.

Do While Not recSetF.EOF

MsgBox recSetF.Fields(«EmployeeId») & «, » & recSetF.Fields(«JoinDate»)

‘set values of filtered records in NewJoinee? field to True:

recSetF.Edit

recSetF.Fields(«NewJoinee?»).Value = True

recSetF.Update

recSetF.MoveNext

End Sub