Relations
DataRelationCollection drc = DataSet.Relations;
Accesses the DataRelationCollection contained in a
DataSet that contains the child
DataRelation objects belonging to the
DataSet. These objects relate tables in the
DataSet using their primary and foreign keys and
allow navigation between parent and child tables in both directions.
The DataRelationCollection has two methods that
are used to add relations to the DataSet. The
first is the Add( ) method, which in its simplest
form takes a single DataRelation argument as shown
in the following example:
DataRelation dr = new DataRelation("MyDataRelation",
parentTable.Columns["PrimaryKeyField"],
childTable.Columns["ForeignKeyField"]);
ds.Relations.Add(dr);The other overloaded versions of the Add( ) method
allow a DataRelation object to be created and
added to the DataSet in a single statement, as
shown in the following example:
DataTable dt1;
DataColumn col1, col2;
// ... code to define columns col1 and col2 and add them to the table dt1
DataTable dt2;
DataColumn col3, col4;
// ... code to define columns col3 and col4 and add them to the table dt2
DataSet ds = new DataSet();
ds.Tables.Add(dt1);
ds.Tables.Add(dt2);
// add a relation to the DataRelationCollection called MyRelation
// and create the ForeignKey constraint between parent col1 and child col3
ds.Relations.Add("MyRelation", col1, col3, true);
// add the relation between parent columns col1 and col2 and child columns
// col3 and col4. Do not create the ForeignKey constraint.
ds.Relations.Add("MyRelation", new DataColumn[] {col1, col2},
new DataColumn[] {col3, col4}, false);More than one DataRelation can be added to a
DataSet in a single statement using the
AddRange( ) method. This method adds
DataRelation objects from a
DataRelation array to the end of the
DataRelationCollection, as the following example
illustrates:
// code to create DataRelations dr1 and dr2
ds.Relations.AddRange(new DataRelation[] {dr1, dr2});The IndexOf( ) method allows the index of an
existing relation to be retrieved from the
DataRelationCollection. This method has two
overloads that allow the relation to be located using either the
relation name or a reference to the relation, as shown in the
following examples:
Int32 index = ds.Relations.IndexOf("MyDataRelation");
Int32 index = ds.Relations.IndexOf(dr);The value returned by the IndexOf( ) method is
zero-based. A value of -1 is returned if the specified relation
object doesn’t exist within the collection.
There are also two methods that can remove a relation from the
DataRelationCollection. The Remove( ) method removes a relation matching the relation name
argument. The RemoveAt( ) method removes the
relation at a specified index from the
DataRelationCollection. The following examples
illustrate both methods:
// remove the relation names MyDataRelation from the
// DataRelationCollection for the DataSet
ds.Relations.Remove("MyDataRelation");
// remove the first relation in the DataRelationCollection for the DataSet
ds.Relations.RemoveAt(0);Finally, the Clear( ) method removes all the
relations from the DataSet, as shown in the
following example:
ds.Relations.Clear();
The commonly used public properties of the
DataRelationCollection are listed and described in
Table 22-9.
The commonly used public methods of the
DataRelationCollection are listed and described in
Table 22-10.