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ConstraintCollection.CollectionChanged Event

Occurs whenever the ConstraintCollection is changed because of Constraint objects being added or removed.

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

public event CollectionChangeEventHandler CollectionChanged

For more information about handling events, see Consuming Events.

The following example demonstrates how to use the CollectionChanged event.

    private static void ConstraintCollectionChanged()
        // Demonstrate ConstraintCollection.CollectionChanged event. 
            // Create Customers table.
            DataTable customersTable = new DataTable("Customers");
            customersTable.Columns.Add("id", typeof(int));
            customersTable.Columns.Add("Name", typeof(string));
            customersTable.Constraints.CollectionChanged += 
                new System.ComponentModel.CollectionChangeEventHandler( 

            // Create Orders table.
            DataTable ordersTable = new DataTable("Orders");
            ordersTable.Columns.Add("CustID", typeof(int));
            ordersTable.Columns.Add("CustName", typeof(string));
            ordersTable.Constraints.CollectionChanged += 
                new System.ComponentModel.CollectionChangeEventHandler(

            // Create unique constraint.
            UniqueConstraint constraint = new UniqueConstraint(
            // Create unique constraint and specify as primary key.
                "pKey", ordersTable.Columns["CustID"], true);

            // Remove constraints.

            // Results in an Exception. You can't remove  
            // a primary key constraint.
        catch(Exception ex)
            // Process exception and return.
            Console.WriteLine("Exception of type {0} occurred.", 

    private static void Collection_Changed(object sender, 
        System.ComponentModel.CollectionChangeEventArgs ex)
        Console.WriteLine("List_Changed Event: '{0}'\t element={1}", 
            ex.Action, ex.Element);

.NET Framework

Supported in: 4.6, 4.5, 4, 3.5, 3.0, 2.0, 1.1, 1.0

.NET Framework Client Profile

Supported in: 4, 3.5 SP1

Windows 8.1, Windows Server 2012 R2, Windows 8, Windows Server 2012, Windows 7, Windows Vista SP2, Windows Server 2008 (Server Core Role not supported), Windows Server 2008 R2 (Server Core Role supported with SP1 or later; Itanium not supported)

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

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