Calling SQL Stored procedure using Dapper

Question

I have following SQL Stored Procedure

GO
SET ANSI_NULLS ON
GO
SET QUOTED_IDENTIFIER ON
GO
ALTER PROCEDURE [dbo].[GetNextNumberTest]
@NEWNUMBER varchar(100) OUTPUT
AS
BEGIN
    SET NOCOUNT ON;
    SET @NEWNUMBER = 'ABC00001'
    RETURN 1
END   

I am trying to read NENUMBER value using dapper, here is my code

private string GetNextNumber()
{
    var dynamicParams = new DynamicParameters();
    dynamicParams.Add("rval", DbType.Int32, direction: ParameterDirection.ReturnValue);
    dynamicParams.Add("NEWNUMBER", DbType.String, direction: ParameterDirection.Output);
    var data = db.QueryMultiple("GetNextNumberTest", dynamicParams, commandType:    CommandType.StoredProcedure);
    var result = dynamicParams.Get<string>("NEWNUMBER");
    return result;
}

But i always get the following error

An exception of type 'System.Data.SqlClient.SqlException' occurred in Dapper.dll but was    not handled in user code

Additional information: Error converting data type varchar to int.

Any help is greatly appreciated.

Answer 1

multiple usage errors:

1. passing DbType.Int32 / DbType.String as the value rather than the data type
2. if you aren't passing a string value, it needs a hint for the length
3. you should use Execute, not QueryMultiple here
4. using the return of Execute to mean the return value of the stored procedure (that simply isn't how ADO.NET works; the return value there is theoretically the rows affected, but it is usually a meaningless number)

So:

dynamicParams.Add("rval", dbType: DbType.Int32,
    direction: ParameterDirection.ReturnValue);
dynamicParams.Add("NEWNUMBER", dbType: DbType.String,
    direction: ParameterDirection.Output, size: 100);
db.Execute("GetNextNumberTest", dynamicParams,
    commandType: CommandType.StoredProcedure);
var rval = dynamicParams.Get<int>("rval");
var result = dynamicParams.Get<string>("NEWNUMBER");