How to use SQL user defined functions in .NET?

Question

I created a scalar function in the DB

SET ANSI_NULLS ON
GO
SET QUOTED_IDENTIFIER ON
GO
ALTER FUNCTION [dbo].[fn_GetUserId_Username]
    (
    @Username varch         


        

Answer 1

This is very similar to the above answer, but the below code allows you to call a UDF with any number of parameters and any return type. This might be useful as a more general solution. This also hasn't been tested thoroughly...I think it will have some problems with varchars.

public class MyDBAccess
{
    private SqlConnection sqlConnection = new SqlConnection("databaseconnectionstring");

    public int GetUserIdByUsername(string username)
    {
        int userID = CallUDF("dbo.fn_GetUserId_Username", new SqlParameter("@Username", username));
        return userID;
    }

    internal static T1 CallUDF(string strUDFName, params SqlParameter[] aspParameters)
    {
        using (SqlConnection scnConnection = sqlConnection)
        using (SqlCommand scmdCommand = new SqlCommand(strUDFName, scnConnection))
        {
            scmdCommand.CommandType = CommandType.StoredProcedure;

            scmdCommand.Parameters.Add("@ReturnValue", TypeToSqlDbType()).Direction = ParameterDirection.ReturnValue;
            scmdCommand.Parameters.AddRange(aspParameters);

            scmdCommand.ExecuteScalar();

            return (T1)scmdCommand.Parameters["@ReturnValue"].Value;
        }
    }

    private SqlDbType TypeToSqlDbType()
    {
        if (typeof(T1) == typeof(bool))
        {
            return SqlDbType.Bit;
        }
        else if (typeof(T1) == typeof(int))
        {
            return SqlDbType.Int;
        }
        //
        // ... add more types here
        //
        else
        {
            throw new ArgumentException("No mapping from type T1 to a SQL data type defined.");
        }
    }
}