Dapper Output parameter interpreted as null by mysql

Question

I am trying to run this simple Dapper example from the test suite in Mysql 5.6.10 (AWS Aurora).

var p = new DynamicParameters(new { a = 1, b = 2 });
p.Add("c", dbType: DbType.Int32, direction:ParameterDirection.Output);
cnn.Execute(@"set @c = @a + @b", p);
var results = p.Get<int>("@c");

However, an exception is being thrown. The @c is being interpreted as NULL>

I would like to use two output parameters to return the number of rows affected by an insert statement and the last inserted ID.

Reproduced on connector 6.9.5 and Dapper 1.42. (and local MySql 5.6.14) — Steve
– Steve, Commented Apr 24, 2016 at 7:08
Definitively the problem is not in Dapper itself. That syntax _set @c = @a + @b" is invalid for MySql also in a standard (non Dapper) query. — Steve
– Steve, Commented Apr 24, 2016 at 12:08
As @Steve notes: if it isn't valid syntax for your flavor of database server, it just isn't going to work. Dapper makes things more convenient, but it doesn't change what the server supports. — Marc Gravell
– Marc Gravell, Commented Apr 24, 2016 at 14:35

Guuours · Accepted Answer · 2017-04-20 11:12:11Z

1

I found it seems impossible to fetch out parameter from mysql with dapper, so I modified you code a bit to achieve the result.

var p = new DynamicParameters(new { a = 1, b = 2 });
//p.Add("c", dbType: DbType.Int32, direction: ParameterDirection.Output);
//conn.Execute(@"set @c = @a + @b", p);
using (var reader = conn.ExecuteReader(@"set @c = @a + @b; select @c;", p))
{
    //var results = p.Get<int>("@c");
    if (reader.Read())
    {
        var result = reader.GetInt32(0);
    }
}

answered Apr 20, 2017 at 11:12

Guuours

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