System.Data Namespace

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Represents a collection of constraints for a DataTable.

ConstraintCollection Class Members

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Properties Visibility Name Value Type Accessibility public Item ( String name ) Constraint [ Get ] public Item ( Int32 index ) Constraint [ Get ]   Methods Visibility Name Parameters Return Type public Add ( String name , DataColumn primaryKeyColumn , DataColumn foreignKeyColumn ) Constraint public Add ( String name , DataColumn primaryKeyColumns , DataColumn foreignKeyColumns ) Constraint public Add ( String name , DataColumn column , Boolean primaryKey ) Constraint public Add ( Constraint constraint ) Void public Add ( String name , DataColumn columns , Boolean primaryKey ) Constraint public AddRange ( Constraint constraints ) Void public CanRemove ( Constraint constraint ) Boolean public Clear ( ) Void public Contains ( String name ) Boolean public CopyTo ( Constraint array , Int32 index ) Void public IndexOf ( String constraintName ) Int32 public IndexOf ( Constraint constraint ) Int32 public Remove ( String name ) Void public Remove ( Constraint constraint ) Void public RemoveAt ( Int32 index ) Void   Events Multicast Name Type multicast CollectionChanged CollectionChangeEventHandler

The ConstraintCollection represents the set of constraints defined for a given DataTable. This collection is accessed via the DataTable.Constraints property.

The ConstraintCollection can contain both UniqueConstraint and ForeignKeyConstraint objects for the table. A UniqueConstraint ensures that data in a given column is always unique to preserve the data integrity. A ForeignKeyConstraint determines what will happen in related tables when data in the DataTable is either updated or deleted.

A UniqueConstraint is created when a DataColumn with its Unique property set to true is added to a DataTable object' s DataColumnCollection. A ForeignKeyConstraint is created when a DataRelation is added to a DataSet object's DataRelationCollection.

NOTE: When a DataRelation is added to to a DataSet, both types of constraint are created automatically. The UniqueConstraint is applied to the primary key column in the parent DataTable, and the constraint is added to that table' s ConstraintCollection. The ForeignKeyConstraint is applied to the primary key column and the foreign key column, and the constraint is added to the child table' s ConstraintCollection.

Like most data collections in ADO.NET, the ConstraintCollection uses standard collection methods such as Add, Clear, and Remove. In addition, the Contains method can be used to check for the existence of a particular constraint in the collection.

ForeignKeyConstraint   UniqueConstraint   DataRelation

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