Database Migrations

Migrations are a convenient way for you to alter your database in a structured and organized manner. You could edit fragments of SQL by hand but you would then be responsible for telling other developers that they need to go and run them. You would also have to keep track of which changes need to be run against the production machines next time you deploy.

The database table migration tracks which migrations have already been run so all you have to do is make sure your migrations are in place and call $migration->latest() to bring the database up to the most recent state. You can also use $migration->setNamespace(null)->latest() to include migrations from all namespaces.

• Migration file names
• Create a Migration
  • Foreign Keys
  • Database Groups
  • Namespaces
• Usage Example
• Command-Line Tools
• Migration Preferences
• Class Reference

Migration file names

Each Migration is run in numeric order forward or backwards depending on the method taken. Each migration is numbered using the timestamp when the migration was created, in YYYYMMDDHHIISS format (e.g. 20121031100537). This helps prevent numbering conflicts when working in a team environment.

Prefix your migration files with the migration number followed by an underscore and a descriptive name for the migration. The year, month, and date can be separated from each other by dashes, underscores, or not at all. For example:

• 20121031100537_add_blog.php
• 2012-10-31-100538_alter_blog_track_views.php
• 2012_10_31_100539_alter_blog_add_translations.php

Create a Migration

This will be the first migration for a new site which has a blog. All migrations go in the app/Database/Migrations/ directory and have names such as 20121031100537_add_blog.php.

<?php namespace App\Database\Migrations;

use CodeIgniter\Database\Migration;

class AddBlog extends Migration
{

        public function up()
        {
                $this->forge->addField([
                        'blog_id'          => [
                                'type'           => 'INT',
                                'constraint'     => 5,
                                'unsigned'       => true,
                                'auto_increment' => true,
                        ],
                        'blog_title'       => [
                                'type'           => 'VARCHAR',
                                'constraint'     => '100',
                        ],
                        'blog_description' => [
                                'type'           => 'TEXT',
                                'null'           => true,
                        ],
                ]);
                $this->forge->addKey('blog_id', true);
                $this->forge->createTable('blog');
        }

        public function down()
        {
                $this->forge->dropTable('blog');
        }
}

The database connection and the database Forge class are both available to you through $this->db and $this->forge, respectively.

Alternatively, you can use a command-line call to generate a skeleton migration file. See below for more details.

Foreign Keys

When your tables include Foreign Keys, migrations can often cause problems as you attempt to drop tables and columns. To temporarily bypass the foreign key checks while running migrations, use the disableForeignKeyChecks() and enableForeignKeyChecks() methods on the database connection.

public function up()
{
        $this->db->disableForeignKeyChecks()

        // Migration rules would go here..

        $this->db->enableForeignKeyChecks();
}

Database Groups

A migration will only be run against a single database group. If you have multiple groups defined in app/Config/Database.php, then it will run against the $defaultGroup as specified in that same configuration file. There may be times when you need different schemas for different database groups. Perhaps you have one database that is used for all general site information, while another database is used for mission critical data. You can ensure that migrations are run only against the proper group by setting the $DBGroup property on your migration. This name must match the name of the database group exactly:

<?php namespace App\Database\Migrations;

use CodeIgniter\Database\Migration;

class AddBlog extends Migration
{
        protected $DBGroup = 'alternate_db_group';

        public function up() { . . . }

        public function down() { . . . }
}

Namespaces

The migration library can automatically scan all namespaces you have defined within app/Config/Autoload.php or loaded from an external source like Composer, using the $psr4 property for matching directory names. It will include all migrations it finds in Database/Migrations.

Each namespace has it’s own version sequence, this will help you upgrade and downgrade each module (namespace) without affecting other namespaces.

For example, assume that we have the following namespaces defined in our Autoload configuration file:

$psr4 = [
        'App'       => APPPATH,
        'MyCompany' => ROOTPATH . 'MyCompany',
];

This will look for any migrations located at both APPPATH/Database/Migrations and ROOTPATH/MyCompany/Database/Migrations. This makes it simple to include migrations in your re-usable, modular code suites.

Usage Example

In this example some simple code is placed in app/Controllers/Migrate.php to update the schema:

<?php namespace App\Controllers;

class Migrate extends \CodeIgniter\Controller
{

        public function index()
        {
                $migrate = \Config\Services::migrations();

                try
                {
                        $migrate->latest();
                }
                catch (\Throwable $e)
                {
                        // Do something with the error here...
                }
        }

}

Command-Line Tools

CodeIgniter ships with several commands that are available from the command line to help you work with migrations. These tools are not required to use migrations but might make things easier for those of you that wish to use them. The tools primarily provide access to the same methods that are available within the MigrationRunner class.

migrate

Migrates a database group with all available migrations:

> php spark migrate

You can use (migrate) with the following options:

• -g - to chose database group, otherwise default database group will be used.
• -n - to choose namespace, otherwise (App) namespace will be used.
• -all - to migrate all namespaces to the latest migration

This example will migrate Blog namespace with any new migrations on the test database group:

> php spark migrate -g test -n Blog

When using the -all option, it will scan through all namespaces attempting to find any migrations that have not been run. These will all be collected and then sorted as a group by date created. This should help to minimize any potential conflicts between the main application and any modules.

rollback

Rolls back all migrations, taking the database group to a blank slate, effectively migration 0:

> php spark migrate:rollback

You can use (rollback) with the following options:

• -g - to choose database group, otherwise default database group will be used.
• -b - to choose a batch: natural numbers specify the batch, negatives indicate a relative batch
• -f - to force a bypass confirmation question, it is only asked in a production environment

refresh

Refreshes the database state by first rolling back all migrations, and then migrating all:

> php spark migrate:refresh

You can use (refresh) with the following options:

• -g - to choose database group, otherwise default database group will be used.
• -n - to choose namespace, otherwise (App) namespace will be used.
• -all - to refresh all namespaces
• -f - to force a bypass confirmation question, it is only asked in a production environment

status

Displays a list of all migrations and the date and time they ran, or ‘–’ if they have not been run:

> php spark migrate:status
Filename               Migrated On
First_migration.php    2016-04-25 04:44:22

You can use (status) with the following options:

• -g - to choose database group, otherwise default database group will be used.

create

Creates a skeleton migration file in app/Database/Migrations. It automatically prepends the current timestamp. The class name it creates is the Pascal case version of the filename.

> php spark migrate:create [filename]

You can use (create) with the following options:

• -n - to choose namespace, otherwise (App) namespace will be used.

Migration Preferences

The following is a table of all the config options for migrations, available in app/Config/Migrations.php.

Preference	Default	Options	Description
enabled	true	true / false	Enable or disable migrations.
table	migrations	None	The table name for storing the schema version number.
timestampFormat	Y-m-d-His_		The format to use for timestamps when creating a migration.

Class Reference

CodeIgniter\Database\MigrationRunner

findMigrations()

Returns:	An array of migration files
Return type:	array

An array of migration filenames are returned that are found in the path property.

latest($group)

Parameters:	$group (mixed) – database group name, if null default database group will be used.
Returns:	true on success, false on failure
Return type:	bool

This locates migrations for a namespace (or all namespaces), determines which migrations have not yet been run, and runs them in order of their version (namespaces intermingled).

regress($batch, $group)

Parameters:	$batch (mixed) – previous batch to migrate down to; 1+ specifies the batch, 0 reverts all, negative refers to the relative batch (e.g. -3 means “three batches back”) $group (mixed) – database group name, if null default database group will be used.
Returns:	true on success, false on failure or no migrations are found
Return type:	bool

Regress can be used to roll back changes to a previous state, batch by batch.

$migration->batch(5);
$migration->batch(-1);

force($path, $namespace, $group)

Parameters:	$path (mixed) – path to a valid migration file. $namespace (mixed) – namespace of the provided migration. $group (mixed) – database group name, if null default database group will be used.
Returns:	true on success, false on failure
Return type:	bool

This forces a single file to migrate regardless of order or batches. Method “up” or “down” is detected based on whether it has already been migrated. Note: This method is recommended only for testing and could cause data consistency issues.

setNamespace($namespace)

Parameters:	$namespace (string) – application namespace.
Returns:	The current MigrationRunner instance
Return type:	CodeIgniter\Database\MigrationRunner

Sets the path the library should look for migration files:

$migration->setNamespace($path)
          ->latest();

setGroup($group)

Parameters:	$group (string) – database group name.
Returns:	The current MigrationRunner instance
Return type:	CodeIgniter\Database\MigrationRunner

Sets the path the library should look for migration files:

$migration->setNamespace($path)
          ->latest();