php - Where condition on third table field in many to many relationship using datamapper -

i have 3 tables-

users(id,name,dob) books(id,title,author) issuedbooks(id,book_id,student_id,issue_date) 

the relationship between user , book many many resulting in third table issuedbooks.

my models are-

class student extends datamapper{     var $table="students";     var $has_many=array(         "books"=>array(             "class"=>"book",             "join_table"=>"issuedbooks",             "join_self_as"=>"student",             "join_other_as"=>"book",             "other_field"=>"students"         )     ); }  class book extends datamapper{     var $table="books";     var $has_many=array(         "students"=>array(             "class"=>"student",             "join_table"=>"issuedbooks",             "join_self_as"=>"book",             "join_other_as"=>"student",             "other_field"=>"books"         )     ); } 

this table issuedbooks has entry like-

id      student_id      book_id  issue_date 1       2               1        2013-07-18  2       2               4        2013-07-16  3       1               5        2013-07-18  4       2               6        2013-07-18 

now have find out books opted student id 2 , issue_date 2013-7-17.

i've tried, won't result.

$student=new student(); $student->get_by_id('2'); $student->books->include_join_fields()->get(); foreach($student->books $book): 

$book->where_join_field($student,'issue_date >',"2013-07-17")->get();

    echo $book->title." ".$book->join_issue_date."<br />"; endforeach; 

please me out, going wrong?

here solution problem, it's simple guess.
, don't have create id column in many-to-many table (issuedbooks).
issuedbooks.book_id , issuedbooks.student_id must primary_keys.

class somemodel extends ci_model {     public function getbooksbystudentidanddate($students_id, $date)     {         $students_id = (int) $students_id;         $date = (date('y-m-d', strtotime($date)) === $date) ? $date : false;          if( ! $students_id or ! $date)             return array();          $this->db->where('issuedbooks.students_id', $students_id);         $this->db->where('issuedbooks.issued_date', $date);          $this->db->select('             users.name,              books.title,              issuedbooks.issued_date date         ');         $this->db->join('users','issuedbooks.students_id=users.id');         $this->db->join('books','issuedbooks.book_id=books.id');         $this->db->order_by('issuedbooks.issued_date', 'asc');          return $this->db->from('issuedbooks')->get()->result_array();     } }