Assembly: System.Data (in system.data.dll)
The DataColumn is the fundamental building block for creating the schema of a DataTable. You build the schema by adding one or more DataColumn objects to the DataColumnCollection. For more information, see Adding Columns to a Table.
Each DataColumn has a DataType property that determines the kind of data the DataColumn contains. For example, you can restrict the data type to integers, or strings, or decimals. Because data that is contained by the DataTable is typically merged back into its original data source, you must match the data types to those in the data source. For more information, see Mapping .NET Framework Data Provider Data Types to .NET Framework Data Types.
Properties such as AllowDBNull, Unique, and ReadOnly put restrictions on the entry and updating of data, thereby helping to guarantee data integrity. You can also use the AutoIncrement, AutoIncrementSeed, and AutoIncrementStep properties to control automatic data generation. For more information about AutoIncrement columns, see Creating AutoIncrement Columns. For more information, see Defining a Primary Key for a Table.
You can also make sure that values in a DataColumn are unique by creating a UniqueConstraint and adding it to the ConstraintCollection of the DataTable to which the DataColumn belongs. For more information, see Adding Constraints to a Table.
The following example creates a DataTable with several DataColumn objects.
Private Sub MakeTable() ' Create a DataTable. Dim table As DataTable = new DataTable("Product") ' Create a DataColumn and set various properties. Dim column As DataColumn = New DataColumn column.DataType = System.Type.GetType("System.Decimal") column.AllowDBNull = False column.Caption = "Price" column.ColumnName = "Price" column.DefaultValue = 25 ' Add the column to the table. table.Columns.Add(column) ' Add 10 rows and set values. Dim row As DataRow Dim i As Integer For i = 0 to 9 row = table.NewRow() row("Price") = i + 1 ' Be sure to add the new row to ' the DataRowCollection. table.Rows.Add(row) Next i End Sub
Windows 98, Windows Server 2000 SP4, Windows CE, Windows Millennium Edition, Windows Mobile for Pocket PC, Windows Mobile for Smartphone, Windows Server 2003, Windows XP Media Center Edition, Windows XP Professional x64 Edition, Windows XP SP2, Windows XP Starter EditionThe Microsoft .NET Framework 3.0 is supported on Windows Vista, Microsoft Windows XP SP2, and Windows Server 2003 SP1.