DataTable.ChildRelations DataTable.ChildRelations DataTable.ChildRelations DataTable.ChildRelations Property

定義

為這個 DataTable 取得子關聯的集合。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

屬性值

DataRelationCollection,其中包含資料表的子關聯。A DataRelationCollection that contains the child relations for the table. 如果沒有任何 DataRelation 物件存在,則會傳回空的集合。An empty collection is returned if no DataRelation objects exist.

範例

下列範例會使用ChildRelations屬性來傳回中的DataTableDataRelation個子系。The following example uses the ChildRelations property to return each child DataRelation in a DataTable. 然後,每個關聯都會當做的GetChildRows方法DataRow中的引數使用,以傳回資料列陣列。Each relation is then used as an argument in the GetChildRows method of the DataRow to return an array of rows. 然後會列印資料列中每個資料行的值。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

備註

DataRelation定義兩個數據表之間的關聯性。A DataRelation defines the relationship between two tables. 通常,兩個數據表會透過包含相同資料的單一欄位進行連結。Typically, two tables are linked through a single field that contains the same data. 例如,包含位址資料的資料表可能會有單一欄位,其中包含代表國家/地區的代碼。For example, a table which contains address data may have a single field containing codes that represent countries/regions. 包含國家/地區資料的第二個數據表會有單一欄位,其中包含可識別國家/地區的程式碼,而此程式碼會插入至第一個資料表中的對應欄位。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. DataRelation然後,至少包含四個資訊片段:(1)第一個資料表的名稱、(2)第一個資料表中的資料行名稱、(3)第二個數據表的名稱,以及(4)第二個數據表中的資料行名稱。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.

適用於

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