ConstraintCollection.CanRemove(Constraint) Method

Definition

Indicates whether a Constraint can be removed.

public:
 bool CanRemove(System::Data::Constraint ^ constraint);
public bool CanRemove (System.Data.Constraint constraint);
member this.CanRemove : System.Data.Constraint -> bool

Parameters

constraint
Constraint

The Constraint to be tested for removal from the collection.

Returns

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

Examples

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

private void TryRemove(DataSet dataSet)
{
    try
    {
        DataTable customersTable = dataSet.Tables["Customers"];
        Constraint constraint = customersTable.Constraints[0];
        Console.WriteLine("Can remove? " + 
            customersTable.Constraints.CanRemove(constraint));
    }
    catch(Exception ex) 
    {
        // Process exception and return.
        Console.WriteLine("Exception of type {0} occurred.", 
            ex.GetType());
    }
}
Private Sub TryRemove(dataSet As DataSet)
    Try
        Dim customersTable As DataTable = dataSet.Tables("Customers")
        Dim constraint As Constraint = customersTable.Constraints(0)
        Console.WriteLine("Can remove? " & _
            customersTable.Constraints.CanRemove(constraint).ToString())

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

Remarks

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.

Applies to