DataTable.ChildRelations Eigenschaft

Definition

Ruft die Auflistung untergeordneter Beziehungen für diese DataTable ab.Gets the collection of child relations for this DataTable.

public:
 property System::Data::DataRelationCollection ^ ChildRelations { System::Data::DataRelationCollection ^ get(); };
[System.ComponentModel.Browsable(false)]
[System.Data.DataSysDescription("DataTableChildRelationsDescr")]
public System.Data.DataRelationCollection ChildRelations { get; }
member this.ChildRelations : System.Data.DataRelationCollection
Public ReadOnly Property ChildRelations As DataRelationCollection

Eigenschaftswert

Eine DataRelationCollection, die die untergeordneten Beziehungen für die Tabelle enthält.A DataRelationCollection that contains the child relations for the table. Wenn keine DataRelation-Objekte vorhanden sind, wird eine leere Auflistung zurückgegeben.An empty collection is returned if no DataRelation objects exist.

Attribute

Beispiele

Im folgenden Beispiel wird die ChildRelations-Eigenschaft verwendet, um jedes untergeordnete DataRelation in einem DataTablezurückzugeben.The following example uses the ChildRelations property to return each child DataRelation in a DataTable. Jede Beziehung wird dann als Argument in der GetChildRows-Methode des DataRow verwendet, um ein Array von Zeilen zurückzugeben.Each relation is then used as an argument in the GetChildRows method of the DataRow to return an array of rows. Anschließend wird der Wert jeder Spalte in der Zeile ausgegeben.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

Hinweise

Eine DataRelation die die Beziehung zwischen zwei Tabellen definiert.A DataRelation defines the relationship between two tables. In der Regel werden zwei Tabellen durch ein einzelnes Feld verknüpft, das dieselben Daten enthält.Typically, two tables are linked through a single field that contains the same data. Beispielsweise kann eine Tabelle, die Adressdaten enthält, ein einzelnes Feld enthalten, das Codes enthält, die Länder/Regionen darstellen.For example, a table which contains address data may have a single field containing codes that represent countries/regions. Eine zweite Tabelle, die Land-/Regionsdaten enthält, verfügt über ein einzelnes Feld, das den Code enthält, der das Land/die Region identifiziert, und der Code, der in das entsprechende Feld in der ersten Tabelle eingefügt wird.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. Eine DataRelationenthält dann mindestens vier Informationen: (1) den Namen der ersten Tabelle, (2) den Spaltennamen in der ersten Tabelle, (3) den Namen der zweiten Tabelle und (4) den Spaltennamen in der zweiten Tabelle.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.

Gilt für:

Siehe auch