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Constraint Class

Represents a constraint that can be enforced on one or more DataColumn objects.

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

public ref class Constraint abstract

A constraint is a rule used to maintain the integrity of the data in the DataTable. For example, when you delete a value that is used in one or more related tables, a ForeignKeyConstraint determines whether the values in the related tables are also deleted, set to null values, set to default values, or whether no action occurs. A UniqueConstraint, on the other hand, just makes sure that all values within a particular table are unique. For more information, see DataTable Constraints (ADO.NET).

A base Constraint constructor is not used. Primary or unique key constraints are created by using the UniqueConstraint constructor, and foreign key constraints are created by using the ForeignKeyConstraint constructor.

The following example examines the collection of constraints for a DataTable and determines whether each constraint is a UniqueConstraint or a ForeignKeyConstraint. The properties of the constraint are then displayed.

No code example is currently available or this language may not be supported.

This type is safe for multithreaded read operations. You must synchronize any write operations.

Windows 7, Windows Vista, Windows XP SP2, Windows XP Media Center Edition, Windows XP Professional x64 Edition, Windows XP Starter Edition, Windows Server 2008 R2, Windows Server 2008, Windows Server 2003, Windows Server 2000 SP4, Windows Millennium Edition, Windows 98, Windows CE, Windows Mobile for Smartphone, Windows Mobile for Pocket PC, Xbox 360, Zune

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

.NET Framework

Supported in: 3.5, 3.0, 2.0, 1.1, 1.0

.NET Compact Framework

Supported in: 3.5, 2.0, 1.0

XNA Framework

Supported in: 3.0, 2.0, 1.0