DataTable.PrimaryKey 属性 (System.Data)

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public:
 property cli::array <System::Data::DataColumn ^> ^ PrimaryKey { cli::array <System::Data::DataColumn ^> ^ get(); void set(cli::array <System::Data::DataColumn ^> ^ value); };

[System.ComponentModel.TypeConverter(typeof(System.Data.PrimaryKeyTypeConverter))]
public System.Data.DataColumn[] PrimaryKey { get; set; }

public System.Data.DataColumn[] PrimaryKey { get; set; }

[System.ComponentModel.TypeConverter(typeof(System.Data.PrimaryKeyTypeConverter))]
[System.Data.DataSysDescription("DataTablePrimaryKeyDescr")]
public System.Data.DataColumn[] PrimaryKey { get; set; }

[<System.ComponentModel.TypeConverter(typeof(System.Data.PrimaryKeyTypeConverter))>]
member this.PrimaryKey : System.Data.DataColumn[] with get, set

member this.PrimaryKey : System.Data.DataColumn[] with get, set

[<System.ComponentModel.TypeConverter(typeof(System.Data.PrimaryKeyTypeConverter))>]
[<System.Data.DataSysDescription("DataTablePrimaryKeyDescr")>]
member this.PrimaryKey : System.Data.DataColumn[] with get, set

Public Property PrimaryKey As DataColumn()

第一个示例演示如何返回在 a DataGrid 中显示的主键列 DataTable 。第二个示例演示如何为 a DataTable 设置主键列。


   private void GetPrimaryKeys(DataTable table)
    // Create the array for the columns.
    DataColumn[] columns;
    columns = table.PrimaryKey;
    // Get the number of elements in the array.
    Console.WriteLine($"Column Count: {columns.Length}");
    for (int i = 0; i < columns.Length; i++)
        Console.WriteLine($"{columns[i].ColumnName} {columns[i].DataType}");
private void SetPrimaryKeys()
    // Create a new DataTable and set two DataColumn objects as primary keys.
    var table = new DataTable();
    var keys = new DataColumn[2];
    DataColumn column;
    // Create column 1.
    column = new DataColumn();
    column.DataType = Type.GetType("System.String");
    column.ColumnName= "FirstName";
    // Add the column to the DataTable.Columns collection.
    table.Columns.Add(column);
    // Add the column to the array.
    keys[0] = column;
    // Create column 2 and add it to the array.
    column = new DataColumn();
    column.DataType = Type.GetType("System.String");
    column.ColumnName = "LastName";
    table.Columns.Add(column);
    // Add the column to the array.
    keys[1] = column;
    // Set the PrimaryKeys property to the array.
    table.PrimaryKey = keys;
   
    Private Sub GetPrimaryKeys(table As DataTable)
    ' Create the array for the columns.
    Dim columns As DataColumn()
    columns = table.PrimaryKey
    ' Get the number of elements in the array.
    Console.WriteLine($"Column Count: {columns.Length}")
    For i = 0 To columns.GetUpperBound(0)
        Console.WriteLine($"{columns(i).ColumnName} {columns(i).DataType}")
End Sub
Private Sub SetPrimaryKeys()
    ' Create a new DataTable and set two DataColumn objects as primary keys.
    Dim table As New DataTable()
    Dim keys(1) As DataColumn
    Dim column  As DataColumn
    ' Create column 1.
    column = New DataColumn()
    column.DataType = Type.GetType("System.String")
    column.ColumnName= "FirstName"
    ' Add the column to the DataTable.Columns collection.
    table.Columns.Add(column)
    ' Add the column to the array.
    keys(0) = column
    ' Create column 2 and add it to the array.
    column = New DataColumn()
    column.DataType = Type.GetType("System.String")
    column.ColumnName = "LastName"
    table.Columns.Add(column)
    ' Add the column to the array.
    keys(1) = column
    ' Set the PrimaryKeys property to the array.
    table.PrimaryKey = keys
End Sub
    
     表的主键必须是唯一的，才能标识表中的记录。 还可以使用由两列或更多列组成的主键的表。 当单个列不能包含足够的唯一值时，将发生这种情况。 例如，两列主键可能包含“OrderNumber”和“ProductID”列。 由于主键可以由多个列组成，因此
     
      PrimaryKey
     
     该属性由对象数组
     
      DataColumn
     
     组成。