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Compensator Class

Represents the base class for all Compensating Resource Manager (CRM) Compensators.

Namespace:  System.EnterpriseServices.CompensatingResourceManager
Assembly:  System.EnterpriseServices (in System.EnterpriseServices.dll)

'Declaration
Public Class Compensator _
	Inherits ServicedComponent
'Usage
Dim instance As Compensator

The user should extend from this object in order to write a custom transaction Compensator.

A Compensator must always have a public constructor; otherwise, the recovery engine cannot create it.

For more information, see How to: Create a Compensating Resource Manager (CRM).

The following code example demonstrates the use of this class.

' A CRM Compensator 

Public Class AccountCompensator
    Inherits Compensator

    Private receivedPrepareRecord As Boolean = False 


    Public Overrides Sub BeginPrepare() 

    End Sub 'BeginPrepare

    ' nothing to do 
    Public Overrides Function PrepareRecord(ByVal log As LogRecord) As Boolean  

        ' Check the validity of the record. 
        If log Is Nothing Then 
            Return True 
        End If 
        Dim record As [Object]() = log.Record

        If record Is Nothing Then 
            Return True 
        End If 
        If record.Length <> 2 Then 
            Return True 
        End If  
        ' The record is valid.
        receivedPrepareRecord = True 
        Return False 

    End Function 'PrepareRecord

    Public Overrides Function EndPrepare() As Boolean  
        ' Allow the transaction to proceed onlyif we have received a prepare record. 
        If receivedPrepareRecord Then 
            Return True 
        Else 
            Return False 
        End If 

    End Function 'EndPrepare

    Public Overrides Sub BeginCommit(ByVal commit As Boolean) 

    End Sub 'BeginCommit

    ' nothing to do 
    Public Overrides Function CommitRecord(ByVal log As LogRecord) As Boolean  
        ' nothing to do 
        Return False 

    End Function 'CommitRecord

    Public Overrides Sub EndCommit() 

    End Sub 'EndCommit

    ' nothing to do 
    Public Overrides Sub BeginAbort(ByVal abort As Boolean) 

    End Sub 'BeginAbort

    ' nothing to do 
    Public Overrides Function AbortRecord(ByVal log As LogRecord) As Boolean  

        ' Check the validity of the record. 
        If log Is Nothing Then 
            Return True 
        End If 
        Dim record As [Object]() = log.Record

        If record Is Nothing Then 
            Return True 
        End If 
        If record.Length <> 2 Then 
            Return True 
        End If  
        ' Extract old account data from the record. 
        Dim filename As String = CStr(record(0))
        Dim balance As Integer = Fix(record(1))

        ' Restore the old state of the account.
        AccountManager.WriteAccountBalance(filename, balance)

        Return False 

    End Function 'AbortRecord

    Public Overrides Sub EndAbort() 

    End Sub 'EndAbort
End Class 'AccountCompensator ' nothing to do

This compensator is used by the following worker class.

' A CRM Worker
<Transaction()>  _
Public Class Account
    Inherits ServicedComponent

    ' A data member for the account file name. 
    Private filename As String 


    Public Property Filenam() As String 
        Get 
            Return Filename
        End Get 
        Set(ByVal value As String)
            filename = Value
        End Set 
    End Property 


    ' A boolean data member that determines whether to commit or abort the transaction. 
    Private commit As Boolean 


    Public Property AllowCommit() As Boolean  
        Get 
            Return commit
        End Get 
        Set
            commit = value
        End Set 
    End Property 




    ' Debit the account,  
    Public Sub DebitAccount(ByVal ammount As Integer) 

        ' Create a new clerk using the AccountCompensator class. 
        Dim clerk As New Clerk(GetType(AccountCompensator), "An account transaction compensator", CompensatorOptions.AllPhases)
        ' Create a record of previous account status, and deliver it to the clerk. 
        Dim balance As Integer = AccountManager.ReadAccountBalance(Filenam)

        Dim record(1) As [Object]
        record(0) = filename
        record(1) = balance

        clerk.WriteLogRecord(record)
        clerk.ForceLog()
        ' Perform the transaction
        balance -= ammount
        AccountManager.WriteAccountBalance(filename, balance)

        ' Commit or abort the transaction  
        If commit Then
            ContextUtil.SetComplete()
        Else
            ContextUtil.SetAbort()
        End If 
    End Sub 'DebitAccount ' 

End Class 'Account

The following code example demonstrates a client that exercises this compensator and worker.

Imports System



Public Class CrmClient


    Public Shared Sub Main() 

        ' Create a new account object. The object is created in a COM+ server application. 
        Dim account As New Account()

        ' Transactionally debit the account. 
        Try
            account.Filenam = System.IO.Path.GetFullPath("JohnDoe")
            account.AllowCommit = True
            account.DebitAccount(3)
        Finally
            account.Dispose()
        End Try 

    End Sub 'Main 
End Class 'CrmClient

System.Object
  System.MarshalByRefObject
    System.ContextBoundObject
      System.EnterpriseServices.ServicedComponent
        System.EnterpriseServices.CompensatingResourceManager.Compensator

Any public static (Shared in Visual Basic) members of this type are thread safe. Any instance members are not guaranteed to be thread safe.

Windows 7, Windows Vista, Windows XP SP2, Windows XP Media Center Edition, Windows XP Professional x64 Edition, Windows XP Starter Edition, Windows Server 2008 R2, Windows Server 2008, Windows Server 2003, Windows Server 2000 SP4, Windows Millennium Edition, Windows 98

The .NET Framework and .NET Compact Framework do not support all versions of every platform. For a list of the supported versions, see .NET Framework System Requirements.

.NET Framework

Supported in: 3.5, 3.0, 2.0, 1.1, 1.0
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