DataTable.ChildRelations Property

Definition

Namespace:

System.Data

Assembly:

System.Data.Common.dll

Source:

DataTable.cs

Gets the collection of child relations for this DataTable.

public:
 property System::Data::DataRelationCollection ^ ChildRelations { System::Data::DataRelationCollection ^ get(); };

[System.ComponentModel.Browsable(false)]
public System.Data.DataRelationCollection ChildRelations { get; }

[<System.ComponentModel.Browsable(false)>]
member this.ChildRelations : System.Data.DataRelationCollection

Public ReadOnly Property ChildRelations As DataRelationCollection

Property Value

DataRelationCollection

A DataRelationCollection that contains the child relations for the table. An empty collection is returned if no DataRelation objects exist.

Attributes

BrowsableAttribute

Examples

The following example uses the ChildRelations property to return each child DataRelation in a DataTable. Each relation is then used as an argument in the GetChildRows method of the DataRow to return an array of rows. The value of each column in the row is then printed.

private static void GetChildRowsFromDataRelation()
{
    /* For each row in the table, get the child rows using the
    ChildRelations. For each item in the array, print the value
    of each column. */
    DataTable table = CreateDataSet().Tables["Customers"];
    DataRow[] childRows;
    foreach(DataRelation relation in table.ChildRelations)
    {
        foreach(DataRow row in table.Rows)
        {
            PrintRowValues(new DataRow[] {row}, "Parent Row");
            childRows = row.GetChildRows(relation);
            // Print values of rows.
            PrintRowValues(childRows, "child rows");
        }
    }
}

public static DataSet CreateDataSet()
{
    // create a DataSet with one table, two columns
    DataSet dataSet = new DataSet();

    // create Customer table
    DataTable table = new DataTable("Customers");
    dataSet.Tables.Add(table);
    table.Columns.Add("customerId", typeof(int)).AutoIncrement = true;
    table.Columns.Add("name", typeof(string));
    table.PrimaryKey = new DataColumn[] { table.Columns["customerId"] };

    // create Orders table
    table = new DataTable("Orders");
    dataSet.Tables.Add(table);
    table.Columns.Add("orderId", typeof(int)).AutoIncrement = true;
    table.Columns.Add("customerId", typeof(int));
    table.Columns.Add("amount", typeof(double));
    table.PrimaryKey = new DataColumn[] { table.Columns["orderId"] };

    // create relation
    dataSet.Relations.Add(dataSet.Tables["Customers"].Columns["customerId"],
        dataSet.Tables["Orders"].Columns["customerId"]);

    // populate the tables
    int orderId = 1;
    for(int customerId=1; customerId<=10; customerId++)
    {
        // add customer record
        dataSet.Tables["Customers"].Rows.Add(
            new object[] { customerId,
            string.Format("customer{0}", customerId) });
    
        // add 5 order records for each customer
        for(int i=1; i<=5; i++)
        {
            dataSet.Tables["Orders"].Rows.Add(
                new object[] { orderId++, customerId, orderId * 10 });
        }
    }

    return dataSet;
}

private static void PrintRowValues(DataRow[] rows, string label)
{
    Console.WriteLine("\n{0}", label);
    if(rows.Length <= 0)
    {
        Console.WriteLine("no rows found");
        return;
    }
    foreach(DataRow row in rows)
    {
        foreach(DataColumn column in row.Table.Columns)
        {
            Console.Write("\table {0}", row[column]);
        }
        Console.WriteLine();
    }
}

Public Sub GetChildRowsFromDataRelation()
    ' For each row in the table, get the child rows using the
    ' ChildRelations. For each item in the array, print the value
    ' of each column.
    Dim table As DataTable = CreateDataSet().Tables("Customers")

    Dim childRows() As DataRow
    Dim relation as DataRelation
    Dim row as DataRow
    For Each  relation In table.ChildRelations
        For Each row In table.Rows
            PrintRowValues(new DataRow() {row}, "Parent Row")
            childRows = row.GetChildRows(relation)
            ' Print values of rows.
            PrintRowValues(childRows, "child rows")
        Next row
    Next relation
End Sub

Public Function CreateDataSet() As DataSet
    ' create a DataSet with one table, two columns
    Dim dataSet As DataSet
    dataSet = new DataSet()

    ' create Customer table
    Dim table As DataTable
    table = new DataTable("Customers")

    dataSet.Tables.Add(table)
    table.Columns.Add("customerId", _
        GetType(Integer)).AutoIncrement = true
    table.Columns.Add("name", GetType(String))
    table.PrimaryKey = new DataColumn() _
        { table.Columns("customerId") }

    ' create Orders table
    table = new DataTable("Orders")
    dataSet.Tables.Add(table)
    table.Columns.Add("orderId", GetType(Integer)).AutoIncrement = true
    table.Columns.Add("customerId", GetType(Integer))
    table.Columns.Add("amount", GetType(Double))
    table.PrimaryKey = new DataColumn() { table.Columns("orderId") }

    ' create relation
    dataSet.Relations.Add(dataSet.Tables("Customers").Columns("customerId"), _
        dataSet.Tables("Orders").Columns("customerId"))
    
    ' populate the tables
    Dim orderId As Integer = 1
    Dim customerId As Integer
    Dim i As Integer
    For customerId = 1 To 10
        ' add customer record
        dataSet.Tables("Customers").Rows.Add( _
            new object() { customerId, _
            string.Format("customer{0}", customerId) })
        
        ' add 5 order records for each customer

        For i = 1 To 5
            dataSet.Tables("Orders").Rows.Add( _
                new object() { orderId, customerId, orderId * 10 })
        
        orderId = orderId+1 
    Next
    Next

    CreateDataSet = dataSet
End Function

private sub PrintRowValues(rows() As DataRow, label As String)
    Console.WriteLine("\n{0}", label)
    If rows.Length <= 0
        Console.WriteLine("no rows found")
        Exit Sub
    End If

    Dim row As DataRow
    Dim column As DataColumn

    For Each row In rows
        For Each column In row.Table.Columns
            Console.Write("\table {0}", row(column))
        Next column
        Console.WriteLine()
    Next row
End Sub

Remarks

A DataRelation defines the relationship between two tables. Typically, two tables are linked through a single field that contains the same data. For example, a table which contains address data may have a single field containing codes that represent countries/regions. A second table that contains country/region data will have a single field that contains the code that identifies the country/region, and it is this code which is inserted into the corresponding field in the first table. A DataRelation, then, contains at least four pieces of information: (1) the name of the first table, (2) the column name in the first table, (3) the name of the second table, and (4) the column name in the second table.

See also

• ParentRelations
• GetParentRows(String)
• GetChildRows(String)
• DataTables