January 18, 2010
C# Extension Methods for IDataReader
My team often starts Tuesday morning status meetings with a round of win/learn/fun - a team-building exercise where each person gets to mention an exciting "win", something they learned in the last week, or just something fun. Several weeks ago someone brought up C# Extension Methods as a learn. I could see the potential, but I didn't immediately think of any practical examples.
Fast forward: working on an application at home, and started the
data layer. I was reminded that I am annoyed the fact that
IDataReader does not have a GetString(colName: string)
method (or other data types). Instead, you must use
reader.GetString(reader.GetOrdinal(colName)). And you
must watch out for null values. Suddenly struck me that this would
be a good candidate for an extension method. So I created the
following:
public static class IDataReaderExtensions
{
public static string GetStringFromName(this IDataReader reader, string colName)
{
string value = string.Empty;
if (!reader.IsDBNull(reader.GetOrdinal(colName)))
{
value = reader.GetString(reader.GetOrdinal(colName));
}
return value;
}
}
Note that I have purposefully chosen to use empty strings
instead of nulls, because that is the appropriate response for this
domain. I also chose to name the function GetStringFromName because
I prefer avoiding the confusion of having the same name as a
fundamental method on the interface. Finally, use the function: add
using directive for the namespace, and then
string colValue = reader.GetStringFromName(colName);.
Now I just need to spend a few minutes creating similar methods for
the other data types. Optionally I could add in custom error handling
for situations where the column does not exist, or the reader does
not have any data, etc.
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