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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
/** @event */
public void add_CollectionChanged (CollectionChangeEventHandler value)

/** @event */
public void remove_CollectionChanged (CollectionChangeEventHandler value)

JScript supports the use of events, but not the declaration of new ones.

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.
    try
    {
        // 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( 
            Collection_Changed);

        // 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(
            Collection_Changed);

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

        // Remove constraints.
        customersTable.Constraints.RemoveAt(0);

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


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


Windows 98, Windows 2000 SP4, Windows CE, Windows Millennium Edition, Windows Mobile for Pocket PC, Windows Mobile for Smartphone, Windows Server 2003, Windows XP Media Center Edition, Windows XP Professional x64 Edition, Windows XP SP2, Windows XP Starter Edition

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

.NET Framework

Supported in: 2.0, 1.1, 1.0

.NET Compact Framework

Supported in: 2.0, 1.0

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