Setting primary keys for a DataTable

Gets or sets an array of columns which function as primary keys for the data table.

[Visual Basic]
<Serializable>
Public Property PrimaryKey as DataColumn ()
[C #]
[Serializable]
Public datacolumn[] PrimaryKey {get; set;}
[C + +]
[Serializable]
Public: __property datacolumn* Get_primarykey ();
Public: __property void Set_primarykey (datacolumn*[]);
[JScript]
Public
Serializable
function Get PrimaryKey (): datacolumn[];
Public function set PrimaryKey (datacolumn[]);
Property Value
An array of DataColumn objects.

Exceptions
Exception Type Condition
DataException The key is a foreign key.

Remarks
The primary key of a table must is unique to identify the record in the table. It ' s also possible to have a table with a primary key made up of two or more columns. This occurs can ' t contain enough unique values in a single column. For example, a two column primary key might consist of a "FirstName" and "LastName" column. Because primary keys can be made up to more than one column, the PrimaryKey property consists of an array of DataColumn OB Jects.

Example
[Visual Basic, C #] The "example" shows how to return the primary key columns for a DataTable, displayed in a DataGrid. The second example demonstrates to set the primary key columns for a DataTable.

[Visual Basic]
Private Sub Getprimarykeys (myTable as DataTable)
' Create the array for the columns.
Dim Colarr () as DataColumn
Colarr = Mytable.primarykey
' Get the # of elements in the array.
Console.WriteLine ("Column Count:" & ColArr.Length.ToString ())
Dim I as Integer
For i = 0 to Colarr.getupperbound (0)
Console.WriteLine (Colarr (i). ColumnName & Colarr (i). Datatype.tostring ())
Next I
End Sub

Private Sub Setprimarykeys ()
' Create a new DataTable and set two DataColumn objects as primary keys.
Dim myTable as DataTable = new DataTable ()
Dim keys (2) as DataColumn
Dim MyColumn as DataColumn
' Create column 1.
MyColumn = New DataColumn ()
Mycolumn.datatype = System.Type.GetType ("System.String")
Mycolumn.columnname= "FirstName"
' Add the column to the DataTable.Columns collection.
MYTABLE.COLUMNS.ADD (MyColumn)
' Add the column to the array.
Keys (0) = MyColumn

' Create column 2 and add it to the array.
MyColumn = New DataColumn ()
Mycolumn.datatype = System.Type.GetType ("System.String")
Mycolumn.columnname = "LastName"
MYTABLE.COLUMNS.ADD (MyColumn)
' Add the column to the array.
Keys (1) = MyColumn
' Set the Primarykeys property to the array.
Mytable.primarykey = Keys
End Sub
[C #]
private void Getprimarykeys (DataTable myTable) {
Create the array for the columns.
Datacolumn[] Colarr;
Colarr = Mytable.primarykey;
Get the number of elements in the array.
Console.WriteLine ("Column Count:" + colarr.length);
for (int i = 0; i < colarr.length; i++) {
Console.WriteLine (Colarr[i]. ColumnName + colarr[i]. DataType);
}
}

private void Setprimarykeys () {
Create a new DataTable and set two DataColumn objects as primary keys.
DataTable myTable = new DataTable ();
Datacolumn[] keys = new datacolumn[2];
DataColumn MyColumn;
Create column 1.
MyColumn = new DataColumn ();
Mycolumn.datatype = System.Type.GetType ("System.String");
Mycolumn.columnname= "FirstName";
ADD the column to the DataTable.Columns collection.
MYTABLE.COLUMNS.ADD (MyColumn);
ADD the column to the array.
Keys[0] = MyColumn;

Create column 2 and add it to the array.
MyColumn = new DataColumn ();
Mycolumn.datatype = System.Type.GetType ("System.String");
Mycolumn.columnname = "LastName";
MYTABLE.COLUMNS.ADD (MyColumn);
ADD the column to the array.
KEYS[1] = MyColumn;
Set the Primarykeys property to the array.
Mytable.primarykey = keys;
}
[C + +, JScript] No example is available for C + + or JScript. To view a Visual Basic or C # example, click the Language Filter button in the upper-left corner of the page.

Requirements
Platforms:windows, Windows NT 4.0, Windows Millennium Edition, Windows xp-based, Windows XP Home Edition, Windows XP Profe Ssional, Windows. NET Server Family