Codeigniter 3 blogging application: whenever a category is deleted, set cat_id of all posts in that category to 1

Question

I am working on a basic blog application with Codeigniter 3.1.8 and Bootstrap 4 .

There is a posts and a categories table. At the moment, the application inserts a category id into the posts table , whenever a post is created (you can not add a post before choosing a category for it), but I have set no foreign key relationship between the two tables (for ease of development) and no cascading .

Now I want to set a special cascading relationship between the two tables: whenever a category is deleted, all posts in that category should have 1 in the cat_id column.

I have created an installation process for the application: after creating a database and providing its credentials to the application/config/database.php file, you can run the Install controller which will create all the necessary tables:

class Install extends CI_Controller {
    public function __construct()
    {
        parent::__construct();
    }

    public function index(){
        // Create all the database tables if there are none
        // by redirecting to the Migrations controller
        $tables = $this->db->list_tables();
        if (count($tables) == 0) {
            redirect('migrate');
        } else {
            redirect('/');
        }
    }
}

The migrations I use to create the posts table are:

public function up(){
  $this->dbforge->add_field(array(
  'id'=>array(
    'type'=>'INT',
    'constraint' => 11,
    'unsigned' => TRUE,
    'auto_increment' => TRUE
  ),

  'author_id'=>array(
    'type'=>'INT',
    'constraint' => 11,
    'unsigned' => TRUE,
  ),

  'cat_id'=>array(
    'type'=>'INT',
    'constraint' => 11,
    'unsigned' => TRUE,
  ),

  'title'=>array(
    'type'=>'VARCHAR',
    'constraint' => 255,
  ),

  'slug'=>array(
    'type'=>'VARCHAR',
    'constraint' => 128,
    'unique' => TRUE,
  ),

  'description'=>array(
    'type'=>'VARCHAR',
    'constraint' => 255,
  ),

  'content'=>array(
    'type'=>'TEXT',
  ),

  'post_image'=>array(
    'type'=>'VARCHAR',
    'constraint' => 255,
  ),

 'created_at'=>array(
    'type'=>'TIMESTAMP',
  ),

 'updated_at'=>array(
    'type'=>'TIMESTAMP',
  ),

));

$this->dbforge->add_key('id', TRUE);
$this->dbforge->create_table('posts');
$this->db->query('ALTER TABLE `posts` ADD FOREIGN KEY(`cat_id`) REFERENCES 'categories'(`id`) ON DELETE SET cat_id to 1;');

}

What shall I replace the last line with (it has illustrative purposes):

$this->db->query('ALTER TABLE `posts` ADD FOREIGN KEY(`cat_id`) REFERENCES 'categories'(`id`) ON DELETE SET cat_id to 1;');

in order to get the desired result?

UPDATE: my database does use InnoDB .

Answer 1

You need to use

`ALTER TABLE `posts` ADD FOREIGN KEY(`cat_id`) REFERENCES 'categories'(`id`) ON DELETE SET DEFAULT 1`

However, be aware that this does not work with InnoDB. https://dev.mysql.com/doc/refman/5.5/en/innodb-foreign-key-constraints.html

Answer 2

Here is an example using php

function_delete_category($id) {

     $this->db->trans_start();

     $this->db->where('cat_id', $id);
     $ct = $this->db->count_all_results('posts');

     if ($ct > 0) {

         $this->db->set('cat_id', 1);
         $this->db->where('cat_id', $id);
         $this->db->update('posts');

     }

     $this->db->delete('categories', array('id' => $id));

     $this->db->trans_complete();

     return $this->db->trans_stats();

}

Answer 3

• Honestly speaking, you should have the cat_id column as the foreign key with a soft delete if the category gets deleted.

• However, if this is so necessary, you can create a trigger for this, for MySQL to take care of the deletion and updation like below:

Trigger SQL:

delimiter //

create trigger update_post_categories_with_1
before delete on categories for each row

begin
    update posts set cat_id = 1 where cat_id = OLD.id;  
end//

delimiter ;