DataTableReader.GetOrdinal(String) Method

Definition

Namespace:

System.Data

Assembly:

System.Data.Common.dll

Source:

DataTableReader.cs

Gets the column ordinal, given the name of the column.

public:
 override int GetOrdinal(System::String ^ name);

public override int GetOrdinal (string name);

override this.GetOrdinal : string -> int

Public Overrides Function GetOrdinal (name As String) As Integer

Parameters

name

String

The name of the column.

Returns

Int32

The zero-based column ordinal.

Exceptions

InvalidOperationException

An attempt was made to read or access a column in a closed DataTableReader.

ArgumentException

The name specified is not a valid column name.

Examples

If you have only a column name, in which case the column name is user supplied, and you must retrieve information from the column, you can use a procedure like the following to extract the required information. In this example, the procedure accepts a column name and returns the data that is contained within that column for the current row in the DataTableReader :

private static object GetValueByName(
    DataTableReader reader, string columnName)
{
    // Consider when to use a procedure like this one carefully:
    // if you're going to retrieve information from a column
    // in a loop, it would be better to retrieve the column
    // ordinal once, store the value, and use the methods
    // of the DataTableReader class directly.
    object columnValue;

    try
    {
        int columnOrdinal = reader.GetOrdinal(columnName);
        columnValue = reader.GetValue(columnOrdinal);
    }
    catch (ArgumentException ex)
    {
        // Throw all other errors back out to the caller.
        columnValue = null;
    }
    return columnValue;
}

Private Function GetValueByName( _
   ByVal reader As DataTableReader, _
   ByVal columnName As String) As Object

   ' Consider when to use a procedure like this one carefully:
   ' If you're going to retrieve information from a column
   ' in a loop, it would be better to retrieve the column
   ' ordinal once, store the value, and use the methods
   ' of the DataTableReader class directly. 
   Dim columnValue As Object

   Try
      Dim columnOrdinal As Integer = reader.GetOrdinal(columnName)
      columnValue = reader.GetValue(columnOrdinal)
   Catch ex As ArgumentException
      ' Throw all other errors back out to the caller.
      columnValue = Nothing
   End Try
   Return columnValue
End Function

Remarks

Because most of the methods provided by the DataTableReader class must be provided with an ordinal column number, you can use the GetOrdinal method to retrieve the column number, given the name of the column.

GetOrdinal performs a case-sensitive lookup first. If it fails, a second case-insensitive search is made. If the column number is not found an IndexOutOfRangeException is thrown.

GetOrdinal is kana-width insensitive.

Because ordinal-based lookups are more efficient than named lookups, it is inefficient to call GetOrdinal within a loop. Save time by calling GetOrdinal one time and assigning the results to an integer variable for use within the loop