ADO: ActiveX Data Objects

Opening and Closing a Connection: Implicit Versus Explicit

The Connection object is used to establish a unique physical connection to a given data source. This connection defines how you can obtain, interact with, and manipulate data from the specified source. While a Connection object is always required, you can choose whether to instantiate a connection explicitly or to allow ADO to create one implicitly on your behalf.

Opening a Connection

Example 4-1 illustrates how to open a Recordset object on a table in a data source without explicitly creating a Connection object.

Example 4-1. Implicit Creation of a Connection Object

' declare and instantiate a Recordset
Dim rst As ADODB.Recordset
Set rst = New ADODB.Recordset

' open the Recordset object and implicitly create a Connection
rst.Open "Titles", _
         "DSN=BiblioDSN", _
         adOpenForwardOnly, _
         adLockReadOnly, _
         adCmdTable
'
' do something

' close the Recordset and clean up
rst.Close
Set rst = Nothing

Don’t worry about not understanding the entire example now -- I will explain everything soon. Do notice, however, how easy it is to open a table within a data source. Example 4-1 relies on no other code to first establish a connection; the simple connection string DSN=BiblioDSN tells ADO that the table, Titles, is in the BiblioDSN data source.

Some objects in ADO -- in particular, the Recordset and the Command objects -- do not require a pre-existing Connection object to operate. Both objects can read and write data to a data source, and ...