DataTableReader.GetSchemaTable Method

Definition

Namespace:

System.Data

Assembly:

System.Data.Common.dll

Source:

DataTableReader.cs

Returns a DataTable that describes the column metadata of the DataTableReader.

public:
 override System::Data::DataTable ^ GetSchemaTable();

public override System.Data.DataTable GetSchemaTable ();

override this.GetSchemaTable : unit -> System.Data.DataTable

Public Overrides Function GetSchemaTable () As DataTable

Returns

DataTable

A DataTable that describes the column metadata.

Exceptions

InvalidOperationException

The DataTableReader is closed.

Examples

The following console application example retrieves schema information about the specified column. Pass the DisplaySchemaTableInfo procedure a DataTableReader and an integer representing the ordinal position of a column within the DataTableReader, and the procedure outputs schema information to the console window.

private static void TestGetSchemaTable()
{
    // Set up the data adapter, using information from
    // the AdventureWorks sample database.
    // Modify the SQL expression to retrieve
    // data from a different table.
    SqlDataAdapter adapter =
        SetupDataAdapter("SELECT * FROM Sales.Customer");

    // Fill the DataTable, retrieving all the schema information.
    adapter.MissingSchemaAction = MissingSchemaAction.AddWithKey;
    DataTable table = new DataTable();
    adapter.Fill(table);

    // Create the DataTableReader, and close it when done.
    using (DataTableReader reader = new DataTableReader(table))
    {
        // Modify the column number to display information
        // about a column other than column 0.
        DisplaySchemaTableInfo(reader, 0);
    }

    Console.WriteLine();
    Console.WriteLine("Press Enter to finish.");
    Console.ReadLine();
}

private static void DisplaySchemaTableInfo(
        DataTableReader reader, int ordinal)
{
    // Given a DataTableReader, display schema
    // information about a particular column.
    try
    {
        DataTable schemaTable = reader.GetSchemaTable();
        DataRow row = schemaTable.Rows[ordinal];
        foreach (DataColumn col in schemaTable.Columns)
        {
            Console.WriteLine("{0}: {1}",
                col.ColumnName, row[col.Ordinal]);
        }
    }
    catch (IndexOutOfRangeException ex)
    {
        Console.WriteLine("{0} is an invalid column number.",
            ordinal);
    }
}

private static SqlDataAdapter SetupDataAdapter(String sqlString)
{
    // Assuming all the default settings, create a
    // SqlDataAdapter working with the AdventureWorks
    // sample database that's available with
    // SQL Server.
    String connectionString =
        "Data source=(local);initial catalog=AdventureWorks;" +
        "Integrated Security=True";
    return new SqlDataAdapter(sqlString, connectionString);
}

Private Sub TestGetSchemaTable()
   ' Set up the data adapter, using information from 
   ' the AdventureWorks sample database.
   ' Modify the SQL expression to retrieve 
   ' data from a different table.
   Dim adapter As SqlDataAdapter = _
      SetupDataAdapter("SELECT * FROM Sales.Customer")

   ' Fill the DataTable, retrieving all the schema information.
   adapter.MissingSchemaAction = MissingSchemaAction.AddWithKey
   Dim table As New DataTable
   adapter.Fill(table)

   ' Create the DataTableReader, and close it when done.
   Using reader As New DataTableReader(table)
      ' Modify the column number to display information
      ' about a column other than column 0.
      DisplaySchemaTableInfo(reader, 0)
   End Using

   Console.WriteLine()
   Console.WriteLine("Press Enter to finish.")
   Console.ReadLine()
End Sub

Private Sub DisplaySchemaTableInfo( _
   ByVal reader As DataTableReader, ByVal ordinal As Integer)

   ' Given a DataTableReader, display schema
   ' information about a particular column.
   Try
      Dim schemaTable As DataTable = reader.GetSchemaTable()
      Dim row As DataRow = schemaTable.Rows(ordinal)
      For Each col As DataColumn In schemaTable.Columns
         Console.WriteLine("{0}: {1}", _
            col.ColumnName, row(col.Ordinal))
      Next
   Catch ex As IndexOutOfRangeException
      Console.WriteLine("{0} is an invalid column number.", _
         ordinal)
   End Try
End Sub

Private Function SetupDataAdapter( _
   ByVal sqlString As String) As SqlDataAdapter
   ' Assuming all the default settings, create a SqlDataAdapter
   ' working with the AdventureWorks sample database that's 
   ' available with SQL Server.
   Dim connectionString As String = _
      "Data Source=(local);" & _
      "Initial Catalog=AdventureWorks;" & _
      "Integrated Security=true"
   Return New SqlDataAdapter(sqlString, connectionString)
End Function

Remarks

The GetSchemaTable method returns metadata about each column in the following order:

DataReader column	Description
ColumnName	The name of the column as it appears in the DataTable.
ColumnOrdinal	The ordinal of the column
ColumnSize	-1 if the ColumnSize (or MaxLength) property of the DataColumn cannot be determined or is not relevant; otherwise, 0 or a positive integer that contains the MaxLength value.
NumericPrecision	If the column type is a numeric type, this is the maximum precision of the column. If the column type is not a numeric data type, this is a null value.
NumericScale	If column data type has a scale component, return the number of digits to the right of the decimal point. Otherwise, return a null value.
DataType	The underlying type of the column.
ProviderType	The indicator of the column's data type. If the data type of the column varies from row to row, this value is Object. This column cannot contain a null value.
IsLong	true if the data type of the column is String and its MaxLength property is -1. Otherwise, false.
AllowDBNull	true if the AllowDbNull constraint is set to true for the column; otherwise, false.
IsReadOnly	true if the column cannot be modified; otherwise false.
IsRowVersion	false, for every column.
IsUnique	true: No two rows in the DataTable can have the same value in this column. IsUnique is guaranteed to be true if the column represents a key by itself or if there is a constraint of type UNIQUE that applies only to this column. false: The column can contain duplicate values in the DataTable. The default of this column is false.
IsKey	true: The column is one of a set of columns that, taken together, uniquely identify the row in the DataTable. The set of columns with IsKey set to true must uniquely identify a row in the DataTable. There is no requirement that this set of columns is a minimal set of columns. This set of columns may be generated from a DataTable primary key, a unique constraint or a unique index. false: The column is not required to uniquely identify the row. This value is true if the column participates in a single or composite primary key. Otherwise, its value is false.
IsAutoIncrement	true: The column assigns values to new rows in fixed increments. false: The column does not assign values to new rows in fixed increments. The default of this column is false.
BaseCatalogName	The name of the catalog in the data store that contains the column. Null if the base catalog name cannot be determined. The default value for this column is a null value.
BaseSchemaName	This value is always Null.
BaseTableName	The name of the DataTable.
BaseColumnName	The name of the column in the DataTable.
AutoIncrementSeed	The value of the DataTable's AutoIncrementSeed property.
AutoIncrementStep	The value of the DataTable's AutoIncrementStep property.
DefaultValue	The value of the DataColumn's DefaultValue property.
Expression	The expression string, if the current column is an expression column and all columns used in the expression belong to the same T:System.Data.DataTable that contains the expression column; otherwise null.
ColumnMapping	The MappingType value associated with the DataColumn. The type can be one of Attribute, Element, Hidden, or SimpleContent. The default value is Element.
BaseTableNamespace	The value of the DataTable's Namespace property.
BaseColumnNamespace	The value of the DataColumn's Namespace property.