Why use the GetOrdinal() Method of the SqlDataReader

Question

What's the difference between reading a value from an SqlDataReader using this syntax:

Dim reader As SqlClient.SqlDataReader
reader("value").ToString()

OR

Dim reader As SqlClient.SqlDataReader
reader.GetString(reader.GetOrdinal("value"))

Answer 1

I think that the reason to use GetOrdinal() is so that you can cache the result and re-use it multiple times for performance.

E.g.

Dim reader As SqlClient.SqlDataReader
int valueOrdinal = reader.GetOrdinal("value");
while ( ... )
{
    var value = reader.GetString(valueOrdinal);
}

Answer 2

GetOrdinal performs a case-sensitive lookup first. If it fails, a second case-insensitive search is made. 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 once and assigning the results to an integer variable for use within the loop.

Source: http://msdn.microsoft.com/en-us/library/system.data.sqlclient.sqldatareader.getordinal.aspx