COM+ Services Support

This section describes how Pervasive's OLE DB provider interacts with Microsoft's COM+ Services.

What is COM+ Services?

COM+ services (Component Object Model) is a Microsoft specific technology used to create business objects in a multi-threaded context. COM+ is primarily designed for, but not limited to, Visual Basic programmers. COM+ allows for rapid creation of multi-tier applications and includes many benefits that would normally have to be implemented by the developer. The benefits of COM+ include

For further information about COM+, see Microsoft's documentation.

COM+ services are an extension to the benefits provided by MTS (Microsoft Transaction Server). MTS is Microsoft's previous business object server implementation. In general, references (in Microsoft and Pervasive documentation) to MTS can be substituted with COM+ services.

Pervasive's OLE DB provider is supported in COM+ services. ADO calls made within COM+ services behave like any ADO client call.

Example of COM+ Services for Visual Basic Programmers

As a Visual Basic programmer, you must be aware of the MTSTransactionMode property. Setting this to anything other than NoTransactions will invoke Microsoft transactions. Please refer to COM+ services documentation for the complete reference of this feature.

The following example demonstrates use of Microsoft Transactions. In order for the calls to GetObjectContext to succeed, you must set the MTSTransactionMode property to something other than NoTransactions. Using Microsoft Transactions will allow Microsoft's Transaction Coordinator to do a two-phase commit.

Public Function UpdatePayroll(employeeID As 
Integer, salary As Currency) 
    On Error GoTo ErrHandler 
    Dim rs As New ADODB.Recordset 
    rs.Index = "employeeID" 
    rs.Open "PayrollTable", 
"Provider=PervasiveOLEDB;Data Source=CompanyDB", 
adOpenDynamic, adLockOptimistic, adCmdTableDirect 
    rs.Seek employeeID, adSeekFirstEQ 
    If rs.EOF = True Then 
        GetObjectContext.SetAbort 
    Else 
        rs!salary = salary 
    End If 
    rs.Update 
    rs.Close 
    rs = Nothing 
    GetObjectContext.SetComplete 
Exit Function 
ErrHandler: 
    GetObjectContext.SetAbort 
    If Not IsNull(rs) Then 
        If rs.State = adStateOpen Then 
            rs.Close 
        End If 
    End If 
    rs = Nothing 
End Function 

However, you could rewrite this business object using ADO transactions (with a connection object). This would allow you to set the MTSTransactionMode property to NoTransactions. Without Microsoft Transactions, you no longer have the overhead of the two-phase commit. Also, objects that do not support transactions are allowed to stay resident in memory, whereas those that do are constructed and destroyed on each reference.

Public Function UpdatePayroll(employeeID As 
Integer, salary As Currency) 
    On Error GoTo ErrHandler 
    Dim cn As New Connection 
    Dim rs As New ADODB.Recordset 
     
    cn.Open "Provider=PervasiveOLEDB;Data 
Source=CompanyDB" 
    cn.BeginTrans 
    rs.Index = "employeeID" 
    rs.Open "PayrollTable", cn, adOpenDynamic, 
adLockOptimistic, adCmdTableDirect 
    rs.Seek employeeID, adSeekFirstEQ 
     
    If rs.EOF = True Then 
        cn.RollbackTrans 
    Else 
        rs!salary = salary 
    End If 
    rs.Update 
    rs.Close 
    cn.CommitTrans 
Exit Function 
ErrHandler: 
    cn.RollbackTrans 
    If Not IsNull(rs) Then 
        If rs.State = adStateOpen Then 
            rs.Close 
        End If 
    End If 
End Function