Using an aliased field in a CodeIgniter DataMapper ORM many-to-one relationship
try to mention a "join_table"=>"where both user and form_data are"other wise datamapper will look for this relation in a separate table named form_datas_users
and try to avoid underscores in table names, datamapper uses it at so many places to identify tables relation internally
I was getting same error. It was caused by lack of parent::__construct() in constructor.