php - Codeigniter datamapper one to many relationship -

i have 2 table rostertype , rostertypepositions

i have created 2 model

class roster_type extends datamapper{      var $table = "rostertype";     var $has_many = array(         'position'  =>  array(             'class' =>  'roster_typeposition',             'other_field'   => 'roster_position',             'join_self_as'    =>  '',             'join_other_as' =>  'rostertype'         )     );     function __construct($id = null){         parent::__construct($id);     }      function getallroster(){          return $this->count();     } }  class roster_typeposition  extends datamapper{      var $table = "rostertypepositions";     var $default_order_by = array('positionindex'=>'asc');     var $has_one = array(         'roster_position'   => array(             'class' =>  'roster_type',             'other_field' => 'position',             'join_self_as'    =>  'rostertype',             'join_other_as' =>  ''         )     );     function __construct($id = null){         parent::__construct($id);     }      function get_all_positions(){         $u =  $this->get_iterated();         foreach ($u $ab=>$d){             echo "<pre>";print_r($d->roster_position->get());echo "</pre>";         }         die();     } } 

but reason getting error

error number: 1146  table 'ad_8cceab3cf7883a5.rostertype_rostertypepositions' doesn't exist  select `rostertype`.* (`rostertype`) left outer join `rostertype_rostertypepositions` position_rostertype_rostertypepositions on `rostertype`.`id` = `position_rostertype_rostertypepositions`.`_id` `position_rostertype_rostertypepositions`.`rostertype_id` =  2  filename: /applications/mamp/htdocs/ibm_bluemix/development/draftbeast-dev/libraries/datamapper.php  line number: 1344 

i dont know how generating table position_rostertype_rostertypepositions. please , doing wrong.

solved taking empty fields in model

class roster_typeposition  extends datamapper{     var $model = 'rostertypepositions';     var $table = "rostertypepositions";     var $default_order_by = array('positionindex'=>'asc');     var $has_one = array(         'roster_position'   => array(             'class' =>  'roster_type',             'other_field' => 'position',             'join_self_as'    =>  'rostertype',         )     ); 

and

class roster_type extends datamapper{     var $model = 'roster_type';     var $table = "rostertype";     var $has_many = array(         'position'  =>  array(             'class' =>  'roster_typeposition',             'other_field'   => 'roster_position',             'join_other_as' =>  'rostertype'         )     );