The ForeignKeyConstraint represents a restriction
on a set of related columns. Usually, you don't
create a ForeignKeyConstraint directly. Instead,
you define and add a DataRelation to the
DataSet.Relations collection. A corresponding
ForeignKeyConstraint is added automatically to the
DataTable.Constraints collection of the child
table. When you have a ForeignKeyConstraint on a
DataTable , certain actions are not allowed (such
as creating a parent that references a nonexistent parent row). You
can disable checking for constraint violations by setting
DataSet.EnforceConstraints to
false .
The ForeignKeyConstraint allows you to configure
what happens when the parent column is updated
(UpdateRule ), or when the parent row is deleted
(DeleteRule ) or has AcceptChanges(
) called on it (AcceptRejectRule ). Out
of these three options, the DeleteRule is the most
commonly used. If you set the DeleteRule to
Rule.Cascade , all child rows are deleted when the
parent row is deleted. If you use Rule.SetNull ,
however, the foreign key field in the child record is set to a
null value. If you use
Rule.SetDefault , the foreign key field is set to
a default value when the parent record is deleted. Finally, if you
use Rule.None (the default), no action is taken.
This results in an error when you attempt to remove a parent with
child rows, when you have the
DataSet.EnforceConstraints property set to
true .
public class ForeignKeyConstraint : Constraint {
// Public Constructors
public ForeignKeyConstraint(DataColumn[ ] parentColumns, DataColumn[ ] childColumns);
public ForeignKeyConstraint(DataColumn parentColumn, DataColumn childColumn);
public ForeignKeyConstraint(string constraintName, DataColumn[ ] parentColumns, DataColumn[ ] childColumns);
public ForeignKeyConstraint(string constraintName, DataColumn parentColumn, DataColumn childColumn);
public ForeignKeyConstraint(string constraintName, string parentTableName, string[ ] parentColumnNames,
string[ ] childColumnNames, AcceptRejectRule acceptRejectRule, Rule deleteRule, Rule updateRule);
// Public Instance Properties
public virtual AcceptRejectRule AcceptRejectRule{set; get; }
public virtual DataColumn[ ] Columns{get; }
public virtual Rule DeleteRule{set; get; }
public virtual DataColumn[ ] RelatedColumns{get; }
public virtual DataTable RelatedTable{get; }
public override DataTable Table{get; } // overrides Constraint
public virtual Rule UpdateRule{set; get; }
// Public Instance Methods
public override bool Equals( object key); // overrides object
public override int GetHashCode( ); // overrides object
}
Constraint