Question

I am trying to call a MySQL stored procedure from .NET that accepts a NULL value in one of the parameters. I build my parameter list from below and I keep getting an error when I set DBNull.Value by looking at the value in Visual Studio shows {}. I am not sure why this is erroring, but doesn’t give any detailed message of why.

 protected IEnumerable<MySqlParameter> BuildParameterList(IEnumerable<KeyValuePair<string, object>> parameters)
        {
            return parameters.Select(parameter => new MySqlParameter(parameter.Key, parameter.Value ?? DBNull.Value)
                                                      {
                                                          IsNullable = parameter.Value == null
                                                      });
        }

Answer 1

Fixed it by doing this. Looks like MySQL didn’t like AnsiString which was the default datatype for null.

protected IEnumerable<MySqlParameter> BuildParameterList(IEnumerable<KeyValuePair<string, object>> parameters)
        {
            foreach (var parameter in parameters)
            {
                var mysqlParameter = new MySqlParameter(parameter.Key, parameter.Value ?? DBNull.Value)
                                 {
                                     IsNullable = parameter.Value == null
                                 };

                if(parameter.Value == null && mysqlParameter.DbType == DbType.AnsiString)
                {
                    mysqlParameter.DbType = DbType.String;
                }


                yield return mysqlParameter;
            }
        }