VB Database Programming

This is not about how to create or design a database, it is about how to connect to a database and manipulate a database using VB. It will work (with some minor alterations) in VBA as well.

There are several ways of connecting to a database (for example, Access), via data bound controls, DAO or ADO. On the whole I do not use data bound controls because I like to keep control of what is happening to the data so the rest is about DAO/ADO.

To start with you need to create a few variables of the following types

• Workspace ADODB.Connection - This is required if you are using Transaction Processes (I will explain later)
• Database - This connects to the database Recordset
• ADODB.Recordset - This is the table/query level variable
• Field ADODB.Field - This allows us to get info about the fields

Connecting to a Database

With an Access database it is possible to connect to the database in 2 ways, JET or ODBC. Personally I use ODBC because the file management is easier; to change the filename or path just use the ODBC administrator in the control panel.

Note: These examples are here to show what to do very simply, some of the commands have more options than are shown so please review the help files for more details.

DAO example - JET Connection

Dim ws as Workspace
Dim db as Database

Set ws=DBEngine.Workspaces(0)
set db=ws.OpenDatabase({databasepath and name})

DAO example - ODBC Connection

Dim ws as Workspace
dim db as database
dim strConnection as string

set ws=DBEngine.Workspaces(0)
let strConnection= "ODBC;DSN=" & DatabaseName & ";UID=" & UserName 
& ";PWD=" & UserPassword
set db=ws.OpenDatabase("", False, False, strConnection)

ADO Example

Dim ad as ADODB.Connection

set ad=New ADODB.Connection
Let ad.ConnectionString= "ODBC;DSN=" & DatabaseName & ";UID=" & 
UserName & ";PWD=" & UserPassword
ad.Open

Opening a Table/Query for Viewing

Now we have the database connection established it is time to look at the data. The following example show how to open a table/query and move through it.

DAO Example

Dim rs as recordset

set rs=db.openrecordset({tablename or SQL})
do while not rs.eof
  'Put the code here for what to do with the information.
  'The field information can be access by the field name
  intID=rs!IDField
  'Or by the order number it is in the list (starting at 0)
  intString=rs.Field(1)
  rs.movenext
loop

ADO example

dim ar as ADODB.recordset

set ar=new adodb.recordset
ar.open {SQL Statement}
do while not ar.EOF
  'Put the code here for what to do with the information.
  'The field information can be access by the field name
  intID=ar!IDField
  'Or by the order number it is in the list (starting at 0)
  intString=ar.Field(1).value
  ar.movenext
loop

Change a Record

To edit/add/delete a record we can do it either using SQL or directly. Both DAO and ADO use the execute method for doing updates by SQL.

DAO

 
Dim rs as recordset

set rs=db.openrecordset({tablename or SQL})
rs.execute "INSERT INTO tb(ID,Name) VALUES (10,Anne)"

ADO

dim ar as ADODB.recordset

set ar=new adodb.recordset
ar.open {SQL Statement}
ar.execute "INSERT INTO tb(ID,Name) VALUES (10,Anne)"

These examples add a new record to the database directly.

DAO - Add New Record

Dim rs as recordset

set rs=db.openrecordset({tablename or SQL})
rs.addnew
rs!ID=intID
rs!Name=strName
rs.update

ADO - Add new record

dim ar as ADODB.recordset

set ar=new adodb.recordset
ar.open {SQL Statement}
ar.addnew
ar!ID=intID
ar!Name=strName
ar.update

These examples show how to edit a record directly, after the recordset is open it checks that there is a record meeting the criteria in the open SQL. If not it creates one.

DAO - Edit record

Dim rs as recordset

set rs=db.openrecordset("SELECT * FROM Tb WHERE tdID=10")
if rs.eof then
  rs.addnew
else
  rs.edit
end if
rs!ID=intID
rs!Name=strName
rs.update

ADO - Edit Record

dim ar as ADODB.recordset

set ar=new adodb.recordset
ar.open "SELECT * FROM Tb WHERE tdID=10"
if ar.eof then
  ar.addnew
else
  ar.edit
end if
ar!ID=intID
ar!Name=strName
ar.update

These examples show how to delete a record directly, after the recordset is open it checks that there is a record meeting the criteria in the open SQL. If not it does not do a delete.

DAO - Delete Record

Dim rs as recordset

set rs=db.openrecordset("SELECT * FROM Tb WHERE tdID=10")
if not rs.eof then
  rs.delete
end if

ADO - Delete Record

Dim ar as ADODB.recordset

set ar=new adodb.recordset
ar.open "SELECT * FROM Tb WHERE tdID=10"
if not ar.eof then
  ar.delete
end if

Note: If you open an object when you have finished with it, close it and set it to nothing. For example...

    rs.close
    set rs=nothing

This is good programming practice and clears the memory.