Dapper with SQL Server output bigint parameter returns int32

Question

I have the following C# code and a SQL Server stored procedure.

private static long GetTestBigintOutput(SqlConnection dbConn) 
{
    var sqlParams = new DynamicParameters();
    sqlParams.Add("@input_param", 1);
    sqlParams.Add("@output_param", SqlDbType.BigInt, direction: ParameterDirection.Output);

    dbConn.Execute("stp_zzz_test_output_bigint", sqlParams, commandType: CommandType.StoredProcedure);

    var output = sqlParams.Get<long>("@output_param");

    return output;
}

static void Main(string[] args) 
{
    Console.WriteLine("Hello World!");

    try 
    {
        var output = GetTestBigintOutput(GetDbConnection());
        Console.WriteLine($"Output = {output}");
    }
    catch (Exception ex) 
    {
        Console.WriteLine(ex.Message);                
    }

    Console.ReadKey();
}

Stored procedure:

CREATE PROCEDURE stp_zzz_test_output_bigint
    (@input_param bigint,
     @output_param bigint OUTPUT)
AS
BEGIN
    SET @output_param = @input_param  
END

The output of this simple console app is

Hello World!
Unable to cast object of type 'System.Int32' to type 'System.Int64'.

Is this to be expected? My other stored procedures return values that are tied to BIGINT columns, but the actual returned value will fit in an Int32. However I can't be sure beforehand what the actual returned value will be and this will change once the program is running.

I know I can change the

var output = sqlParams.Get<long>("@output_param");

to

var output = sqlParams.Get<dynamic>("@output_param");

However I feel that this is a kind of cheating.

Any thoughts?

regards Paul

Answer 1

I don't think the Add method of DynamicParameters accepts SqlDbType as the dbType parameter. It should be DbType instead, so you can try to change following:

sqlParams.Add("@output_param", SqlDbType.BigInt, direction: ParameterDirection.Output);

to that:

sqlParams.Add("@output_param", dbType: DbType.Int64, direction: ParameterDirection.Output);