''ForeignKeyConstraint'' ''serializable'

ForeignKeyConstraint serializable

System.Data (system.data.dll) class

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


System.Object figs/U2192.gif Constraint figs/U2192.gif ForeignKeyConstraint

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    Part I: ADO.NET Tutorial
    Part II: ADO.NET Core Classes
    Part III: API Quick Reference
    Chapter 34. The System.Data Namespace