Re: confusion on interface IDataReader

Hi Peter,

SqlCommand.ExecuteReader will return a SqlDataReader.  Since SqlDataReader
implements the IDataReader interface, it can be assigned to a variable of
the IDataReader interface type, but it is still a SqlDataReader.

Joe
http://www.csharp-station.com

> -----Original Message-----
> From: Discussion relating to the specifics of the C# and Managed C++
> languages [mailto:[email protected]] On Behalf Of Peter Osucha
> Sent: Tuesday, June 06, 2006 2:33 PM
> To: [email protected]
> Subject: [DOTNET-CX] confusion on interface IDataReader
>
> I was looking over some example code that was handling data access to a
> SQL
> db.  A method for the code was similar to....
>
> public IDataReader PerformStoredProcedure_DataReader ( string spName,
> CommandBehavior behavior )
> {
>     IDataReader result = null;
>     SqlCommand cmd = new SqlCommand ( spName, (SqlConnection)Connection );
>     cmd.CommandType = CommandType.StoredProcedure;
>     result = cmd.ExecuteReader ( behavior );
>     return result;
> }
>
> Now what has me confused is that this method returns an object of type
> IDataReader - which I thought (from reviewing MSDN) was not allowed since
> IDataReader is an interface (ie, I thought such a method could return an
> object that implemented IDataReader but not an instance of an IDataReader
> object itself since there really wasn't any such thing as an IDataReader
> object).  IOW, it seems that there should be no problem returning an
> object
> of, say, type SqlDataReader from this method.
>
> I'm obviously not understanding something.  Why is it allowed to return on
> object of type IDataReader here?
>
> Peter
>
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