Create MY_Model or Custom Main Model Class in Codeigniter

First create MY_Model.php in application/core folder. Then create MY_Model class in it and the filename must be same as class name.

<?php
class MY_Model extends CI_Model {
    public function __construct(){
        parent::__construct();
        $this->load->database();
    }
}

*you can also change MY_ prefix to your custom prefix.

Now you should extend MY_model instead of CI_Model in your Model class.

The first thing that comes in our mind is why we need this class when codeigniter already gives us bunch of DB functions in CI_Model class. The only thing that forced me to create this, I do not want code same lines that I use many time in my software. For example I created this method to check if data exist in same pattern based on given parameter:

<?php
class MY_Model extends CI_Model {
    public function __construct(){
        parent::__construct();
        $this->load->database();
    }

    public function CustomCheckData($table, $where){
        $query = $this->db->get_where($table, $where);
        return ($query->num_rows())?true:false;
    }
}

or this example where I am fetching user's avatar from DB:

<?php
    public function CustomUserAvatar($uid){
        $this->db->select('avatar');
        $query = $this->db->get_where('my_user_table', array('userid'=>$uid));
        $db_data = $query->result_array();
        return $fetch[0]['avatar'];
    }
}

I just need to pass 2 - 3 parameters to them and they return me desirable data every time.