Upgrade Database

Documentation

• Database Reference Documentation CodeIgniter 3.x
• Working with Databases Documentation CodeIgniter 4.x

What has been changed

• The functionality in CI3 is basically the same as in CI4.
• Database Caching functionality known from CI3 was removed.
• The method names have changed to camelCase and the Query Builder now needs to be initialized before you can run queries on it.

Upgrade Guide

1. Add your database credentials to app/Config/Database.php. The options are pretty much the same as in CI3. Only some names have changed slightly.
2. Everywhere you have used the database, you have to replace $this->load->database(); with $db = db_connect();.
3. If you use multiple databases, use the following code to load additional databases: $db = db_connect('group_name');.
4. Now you have to change all database queries. The most important change here is to replace $this->db with just $db and adjust the method name and $db. Here are some examples:
   • $this->db->query('YOUR QUERY HERE'); to $db->query('YOUR QUERY HERE');
   • $this->db->simple_query('YOUR QUERY') to $db->simpleQuery('YOUR QUERY')
   • $this->db->escape("something") to $db->escape("something");
   • $this->db->affected_rows(); to $db->affectedRows();
   • $query->result(); to $query->getResult();
   • $query->result_array(); to $query->getResultArray();
   • echo $this->db->count_all('my_table'); to echo $db->table('my_table')->countAll();
5. To use the new Query Builder Class, you have to initialize the builder: $builder = $db->table('mytable');. After that, you can run the queries on the $builder. Here are some examples:
   • $this->db->get() to $builder->get();
   • $this->db->get_where('mytable', array('id' => $id), $limit, $offset); to $builder->getWhere(['id' => $id], $limit, $offset);
   • $this->db->select('title, content, date'); to $builder->select('title, content, date');
   • $this->db->select_max('age'); to $builder->selectMax('age');
   • $this->db->join('comments', 'comments.id = blogs.id'); to $builder->join('comments', 'comments.id = blogs.id');
   • $this->db->having('user_id', 45); to $builder->having('user_id', 45);
6. CI4 does not provide the Database Caching layer known from CI3, so if you need to cache the result, use Caching Driver instead.
7. If you use limit(0) in Query Builder, CI4 returns all records instead of no records due to a bug. But since v4.5.0, you can change the incorrect behavior with a setting. So change the setting. See limit(0) Behavior for details.

Code Example

CodeIgniter Version 3.x

<?php

$query = $this->db->select('title')
             ->where('id', $id)
             ->limit(10, 20)
             ->get('mytable');

CodeIgniter Version 4.x

<?php

$builder = $db->table('mytable');

$query = $builder->select('title')
    ->where('id', $id)
    ->limit(10, 20)
    ->get();