ConstraintCollection.CanRemove Method (Constraint)


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Indicates whether a Constraint can be removed.

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

Public Function CanRemove (
	constraint As Constraint
) As Boolean


Type: System.Data.Constraint

The Constraint to be tested for removal from the collection.

Return Value

Type: System.Boolean

true if the Constraint can be removed from collection; otherwise, false.

The default behavior whenever a DataRelation is added to a DataSet, is to add a ForeignKeyConstraint to the parent table and a UniqueConstraint to the child table. The UniqueConstraint is applied to the primary key column of the parent table, and the ForeignKeyConstraint is applied to the foreign key column of the child table. Because trying to remove the UniqueConstraint before removing the ForeignKeyConstraint causes an exception to be thrown, you should always use the CanRemove method before calling Remove, to make sure that the UniqueConstraint can be removed.

The following example uses the CanRemove method to determine whether a Constraint can be removed, before trying to remove it.

Private Sub TryRemove(dataSet As DataSet)
        Dim customersTable As DataTable = dataSet.Tables("Customers")
        Dim constraint As Constraint = customersTable.Constraints(0)
        Console.WriteLine("Can remove? " & _

    Catch ex As Exception
        ' Process exception and return.
        Console.WriteLine("Exception of type {0} occurred.", _
    End Try
End Sub

.NET Framework
Available since 1.1
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