Why use the GetOrdinal() Method of the SqlDataReader

sqldatareader

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

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

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

Best Answer

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);
}

Related Solutions

C# – SqlDataReader performance differences in accessing values

I’ve just peeked into the .NET source code, and the two access methods are essentially the same. The only difference is that the second does an additional boxing. So the first one corresponds to something like (in case of elementary types):

int key = GetInternalSQLDataAsInt32("Key");

while the second one would be:

int key = (int)(object)GetInternalSQLDataAsInt32("Key");

The GetInternalSQLDataAsInt32(...) function represents the SQL data library machinery of marshalling data from SQL to .NET.

But as pointed above, a more significant difference can be expected between string-based keys and ordinal-based keys.

C# – Can you get the column names from a SqlDataReader

var reader = cmd.ExecuteReader();

var columns = new List<string>();

for(int i=0;i<reader.FieldCount;i++)
{
   columns.Add(reader.GetName(i));
}

var columns = Enumerable.Range(0, reader.FieldCount).Select(reader.GetName).ToList();

Best Answer

Related Solutions

C# – SqlDataReader performance differences in accessing values

C# – Can you get the column names from a SqlDataReader

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