ObjectContext.CreateEntityKey Method (String, Object)

 
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Creates the entity key for a specific object, or returns the entity key if it already exists.

Namespace:   System.Data.Objects
Assembly:  System.Data.Entity (in System.Data.Entity.dll)

Public Function CreateEntityKey (
	entitySetName As String,
	entity As Object
) As EntityKey

Parameters

entitySetName
Type: System.String

The fully qualified name of the entity set to which the entity object belongs.

entity
Type: System.Object

The object for which the entity key is being retrieved.

Return Value

Type: System.Data.EntityKey

The EntityKey of the object.

Exception Condition
ArgumentNullException

When either parameter is null.

ArgumentException

When entitySetName is empty.

-or-

When the type of the entity object does not exist in the entity set.

-or-

When the entitySetName is not fully qualified.

InvalidOperationException

When the entity key cannot be constructed successfully based on the supplied parameters.

If an EntityKey does not exist for the entity, the CreateEntityKey method creates a new key for it.

This method is used to determine whether an object that has the same EntityKey is already attached to the ObjectContext. If an object that has the same EntityKey is already attached, an exception is raised. Use the CreateEntityKey method to try to retrieve the EntityKey of the detached object before calling the Attach method.

The example in this topic is based on the AdventureWorks Sales Model. In this example, CreateEntityKey is used to retrieve the entity key of an existing object.

Private Shared Sub ApplyItemUpdates(ByVal updatedItem As SalesOrderDetail)
    ' Define an ObjectStateEntry and EntityKey for the current object. 
    Dim key As EntityKey
    Dim originalItem As Object

    Using context As New AdventureWorksEntities()
        ' Create the detached object's entity key. 
        key = context.CreateEntityKey("SalesOrderDetails", updatedItem)

        ' Get the original item based on the entity key from the context 
        ' or from the database. 
        If context.TryGetObjectByKey(key, originalItem) Then
            ' Call the ApplyCurrentValues method to apply changes 
            ' from the updated item to the original version. 
            context.ApplyCurrentValues(key.EntitySetName, updatedItem)
        End If

        context.SaveChanges()
    End Using
End Sub

.NET Framework
Available since 3.5
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