如何基于另一个表ID Codeigniter更新一个表

Question

I have two tables, first table is directly associated with the second table. I'm using codeigniter and mysql as my database system.

My first table called exam and its structure on below picture:

This is my second table called exam_assign_classes :

How do I update the second table based on first table id. Sometimes in the edit page a user can add assigned batch or remove number of batch. I have tried counting numbers of rows with matching ids and delete those from second table and then re-insert it but it seems so bad practice?

Answer 1

$this->db->where('`exam_id` IN (SELECT `exam_id` FROM `exam_assign_classes `)', NULL, FALSE);
$this->db->update('exam', $data); 

Answer 2

and this is my updated version of code where i placed bunch of database task in one update condition to update the exam assign table.

View:

 <div class="form-group col-xs-12 col-sm-6 col-md-4"> <span class="input-group-addon"><i class="fa fa-asterisk" aria-hidden="true"></i> <i class="fa fa-calendar" aria-hidden="true"></i> <?php echo get_phrase('select_batchs'); ?></span> <select class="form-control" name="assigned_batch[]" data-plugin="select2" multiple> <?php foreach($program_list as $program): $batch_list = $this->crud_model->get_batchs_by_program_id($program['program_id']); ?> <optgroup label="<?php echo $program['name']; ?>"> <?php foreach($batch_list as $batch): ?> <option value="<?php echo $batch['batch_id']; ?>" <?php foreach($assigned_batchs as $assignedRow){ if($assignedRow['batch_id'] == $batch['batch_id']) echo 'selected';} ?>><?php echo $batch['batch_name']; ?></option> <?php endforeach; ?> </optgroup> <?php endforeach; ?> </select> </div> 

model:

 public function delete_associated_exam_assign($exam_id = '') { $this->db->where('exam_id', $exam_id); $this->db->delete('exam_assign_classes'); return true; } public function insert_associated_exam_assign($data2){ $this->db->insert('exam_assign_classes', $data2); return true; } 

 if($param1 == 'do_update'){ $data['name'] = $this->input->post('exam_title'); $data['start_date'] = $this->input->post('start'); $data['end_date'] = $this->input->post('end'); $data['status'] = $this->input->post('status'); if(isset($_POST['is_entrance'])): $data['entrance_exam'] = $this->input->post('is_entrance'); endif; $exam_id = $param2; // update exam table $this->crud_model->update_exam_details($exam_id, $data); // update exam assign table /*First of all delete all those associated rows with matching ids*/ $this->crud_model->delete_associated_exam_assign($exam_id); /*insert newly assign classes*/ foreach($this->input->post('assigned_batch[]') as $batchs){ $data2['exam_id'] = $exam_id; $data2['batch_id'] = $batchs; $this->crud_model->insert_associated_exam_assign($data2); } $this->session->set_flashdata('flash_message' , get_phrase('data_updated')); redirect(base_url() . 'index.php?admin/exam_list/', 'refresh'); } 

From above code i can achieve what i really need. But i am doing deleting and insert rows while updating fields on exam assign table. But it show down my app performance. so, is it a good practice or not to update the database ??