What is wrong with this code pls

Dear Team,
Please this code can run on view but returns zero or null for total_marks and Average score whenever i run it on controller.
Tell me what i am doing wrong. Thanks 

function testme ($exam_id,$class_id){

$soap_data['exam_id'] = $exam_id;
$soap_data['class_id'] = $class_id;

        $soap_data['year']       = $this->db->get_where('settings' , array('type'=>'running_year'))->row()->description;
        if($soap_data['class_id'] != '' && $soap_data['exam_id'] != ''){


$subjects = $this->db->get_where('subject' , array('class_id' => $class_id , 'year' => $running_year))->result_array();
foreach($subjects as $row){ echo $row['name'];}



$students = $this->db->get_where('enroll' , array('class_id' => $class_id , 'year' => $running_year))->result_array();
    foreach($students as $row){

$total_marks = 0;
            $total_grade_point = 0;
                    foreach($subjects as $row2)
$obtained_mark_query = $this->db->get_where('mark' , array(
'class_id' => $class_id , 
'exam_id' => $exam_id , 
'subject_id' => $row2['subject_id'] , 
'student_id' => $row['student_id'],
'year' => $running_year
));
if ( $obtained_mark_query->num_rows() > 0) {
$obtained_marks = $obtained_mark_query->row()->mark_obtained;
if ($obtained_marks >= 0 && $obtained_marks != '') {
$grade = $this->crud_model->get_grade($obtained_marks);
$total_grade_point += $grade['grade_point'];
}
$total_marks += $obtained_marks;

}

$soap_data['Total_score'] = $total_marks;
$this->db->where('class_id' , $class_id);
$this->db->where('year' , $running_year);
$this->db->from('subject');
$number_of_subjects = $this->db->count_all_results();
$average_score= ($soap_data['Total_score'] / $number_of_subjects);
$avg =  round($average_score,2);
$soap_data['Average_score'] = $avg;
}



        $query = $this->db->get_where('total_mark' , array(
                    'exam_id' => $soap_data['exam_id'],
                        'class_id' => $soap_data['class_id'],
                            'Total_score' => $soap_data['Total_score'],
                                'Average_score' => $soap_data['Average_score'],
                                    'year' => $soap_data['year']
                ));
        if($query->num_rows() < 1) {
           $students = $this->db->get_where('enroll' , array('class_id' => $soap_data['class_id'] , 'year' => $soap_data['year']))->result_array();
            foreach($students as $row) {
               $soap_data['student_id'] = $row['student_id'];
                $this->db->insert('total_mark' , $soap_data);
            }
}
}

}

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Joined CodeIgniter Community 2009.  ( Skype: insitfx )

@soapz,

You might want to try using the CI profiler ( https://www.codeigniter.com/user_guide/g...iling.html ). This will allow you to see the executed query (as well as other useful details) which may give you insight into what is wrong with your query.

What is your process for debugging code?