DataTable.ChildRelations Property

Definition

Gets the collection of child relations for this DataTable.

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

Property Value

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

Attributes

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();
    }
}

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.

Applies to

Product Versions
.NET Core 2.0, Core 2.1, Core 2.2, Core 3.0, Core 3.1, 5, 6, 7, 8, 9
.NET Framework 1.1, 2.0, 3.0, 3.5, 4.0, 4.5, 4.5.1, 4.5.2, 4.6, 4.6.1, 4.6.2, 4.7, 4.7.1, 4.7.2, 4.8, 4.8.1
.NET Standard 2.0, 2.1

See also