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How to: Manage Transactions in the Entity Framework

This topic provides an example of how to define a transaction that coordinates making changes to objects in an object context with other external operations. For more information, see Managing Connections and Transactions.

The example in this topic is based on the AdventureWorks Sales Model. To run the code in this example, you must have already added the AdventureWorks Sales Model to your project and configured your project to use the Entity Framework. To do this, complete the procedure in How to: Use the Entity Data Model Wizard. You must also have Microsoft Windows Message Queuing installed.

Example

This example defines a TransactionScope. The TransactionScope ensures that changes to objects in the object context are coordinated with a message queue. The Entity Framework uses this transaction when it saves changes to the database. When an UpdateException occurs, the operation is retried up to two times. When the operation succeeds, the changes in the object context are accepted. For more information, see Managing Connections and Transactions.

This example uses a long-running object context, which is disposed after the transaction succeeds or after all retries have been attempted.

Imports System
Imports System.Linq
Imports System.Data
Imports System.Data.Objects
Imports System.Messaging
Imports System.Transactions

Class TransactionSample
    Public Shared Sub EnlistTransaction()
        Dim retries As Integer = 3
        Dim queueName As String = ".\Fulfilling"

        ' Define variables that we need to add an item. 
        Dim quantity As Short = 2
        Dim productId As Integer = 750
        Dim orderId As Integer = 43680

        ' Define a long-running object context. 
        Dim context As New AdventureWorksEntities()

        Dim success As Boolean = False

        ' Wrap the operation in a retry loop. 
        For i As Integer = 0 To retries - 1
            ' Define a transaction scope for the operations. 
            Using transaction As New TransactionScope()
                Try
                    ' Define a query that returns a order by order ID. 
                    Dim order = (From o In context.SalesOrderHeaders _
                        Where o.SalesOrderID = orderId _
                        Select o).First()

                    ' Load items for the order, if not already loaded. 
                    ' Do this if the lazy loading is turned off.
                    If Not order.SalesOrderDetails.IsLoaded Then
                        order.SalesOrderDetails.Load()
                    End If

                    ' Load the customer, if not already loaded. 
                    ' Do this if the lazy loading is turned off.
                    If Not order.ContactReference.IsLoaded Then
                        order.ContactReference.Load()
                    End If

                    ' Create a new item for an existing order. 
                    Dim newItem As SalesOrderDetail = SalesOrderDetail.CreateSalesOrderDetail(0, 0, quantity, productId, 1, 0, _
                    0, 0, Guid.NewGuid(), DateTime.Today)

                    ' Add new item to the order. 
                    order.SalesOrderDetails.Add(newItem)

                    ' Save changes pessimistically. This means that changes 
                    ' must be accepted manually once the transaction succeeds. 
                    context.SaveChanges(SaveOptions.DetectChangesBeforeSave)

                    ' Create the message queue if it does not already exist. 
                    If Not MessageQueue.Exists(queueName) Then
                        MessageQueue.Create(queueName)
                    End If

                    ' Initiate fulfilling order by sending a message. 
                    Using q As New MessageQueue(queueName)
                        Dim msg As New System.Messaging.Message([String].Format("<order customerId='{0}'>" & "<orderLine product='{1}' quantity='{2}' />" & "</order>", order.Contact.ContactID, newItem.ProductID, newItem.OrderQty))

                        ' Send the message to the queue. 
                        q.Send(msg)
                    End Using

                    ' Mark the transaction as complete. 
                    transaction.Complete()
                    success = True
                    Exit Try
                Catch ex As Exception
                    ' Handle errors and deadlocks here and retry if needed. 
                    ' Allow an UpdateException to pass through and 
                    ' retry, otherwise stop the execution. 
                    If ex.[GetType]() <> GetType(UpdateException) Then
                        Console.WriteLine(("An error occured. " & "The operation cannot be retried.") + ex.Message)
                        Exit Try
                        ' If we get to this point, the operation will be retried. 
                    End If
                End Try
            End Using
        Next
        If success Then
            ' Reset the context since the operation succeeded. 
            context.AcceptAllChanges()
        Else
            Console.WriteLine("The operation could not be completed in " & retries & " tries.")
        End If

        ' Dispose the object context. 
        context.Dispose()
    End Sub
End Class

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