Migrations

When you start building your application with UserFrosting, you'll no doubt be adding your own tables to the data model. After all, what's the point of having users if there's nothing in your application for them to use?

Though you could add new tables to your database through the command line, phpMyAdmin, MySQL Workbench or another tool, you will probably want something that is portable, allowing you to set up your database on other developers' machines or on your test and production servers. To do this, you should use a migration. Migrations bring version control to your database. If you have ever had to share sql files or manually edit a database schema, you've faced the problem that database migrations solve.

Even if you only have a simple table to create, creating a migration is a good practice. You never know what changes you'll need to do to that table later on. You also don't know when or who will need to create that table again later on a different system or even database provider!

Migrations are also very useful when dealing with Automated Test. Tests can use your migrations to setup a temporary or a test database so your tests are executed in a safe environment, keeping your production database secure.

Migration Structure

A migration is nothing more than a PHP class that uses Eloquent's Schema Builder to create, remove, and modify tables in your database. Migrations can also be used to perform additional setup tasks like seeding your tables with some default values.

When you run the main UserFrosting install script (php bakery migrate), it will first check a special migration table to see which migrations have been run before. If the migration class has a record in this table, the migrate script will simply skip it.

Class namespace

To be picked up by the migrate bakery command, migration class files must be located in the src/Database/Migrations/ directory of your Sprinkle and have the appropriate PSR-4 namespace.

Recall that PSR-4 requires that classes have a namespace that corresponds to their file path, i.e. UserFrosting\Sprinkle\{sprinkleName}\Database\Migrations(where {sprinkleName} is the name of your sprinkle). Crucially, namespaces are case-sensitive and must match the case of the corresponding directories. Also note that dots (.) and dashes (-) are not included in the directories (and namespace) as per PSR-4 rules. The class names must also correspond to these file names; e.g. MembersTable.php must contain a single MembersTable class.

You can also optionally organize your migrations in subdirectories so it's easier to find and manage them. For example:

src/Database/Migrations/v400/
    ├── MembersTable.php
    └── OwlsTable.php
src/Database/Migrations/SneksNStuff/
    ├── SneksTable.php
    └── VolesTable.php
src/Database/Migrations/v500/
    ├── OwlsTable.php
    └── MembersTable.php

While multiple operations can be done in the same migration class, it is recommended to use one class per table (or operation). This way, if something goes wrong while creating one of the tables for example, the table previously created won't be created again when running the migrate command again. Plus, every change made before the error occurred can even be reverted using the migrate:rollback command.

Up and down we go

Each migration class needs to extend the base UserFrosting\Sprinkle\Core\Database\Migration class. A migration class must contains two methods: up and down. The up method is used to add new tables, columns, or indexes to your database, while the down method should simply reverse the operations performed by the up method.

Within both of these methods you may use the Laravel schema builder (available in the $this->schema property) to expressively create and modify tables. To learn about all of the methods available on the Schema builder, check out Laravel documentation.

For a simple example, suppose that you want to create a members table, which will be used to add application-specific fields for our users:

<?php

namespace UserFrosting\Sprinkle\MySprinkle\Database\Migrations;

use Illuminate\Database\Schema\Blueprint;
use Illuminate\Database\Schema\Builder;
use UserFrosting\Sprinkle\Core\Database\Migration;

class MembersTable extends Migration
{
    public function up()
    {
        if (!$this->schema->hasTable('members')) {
            $this->schema->create('members', function (Blueprint $table) {
                $table->increments('id');
                $table->integer('user_id')->unsigned()->unique();
                $table->string('city', 255)->nullable();
                $table->timestamps();

                $table->engine = 'InnoDB';
                $table->collation = 'utf8_unicode_ci';
                $table->charset = 'utf8';
                $table->foreign('user_id')->references('id')->on('users');
                $table->index('user_id');
            });
        }
    }

    public function down()
    {
        $this->schema->drop('members');
    }
}

$this->schema is a variable created by the base migration class, which models your database structure. In this example, we call hasTable to check if the members table already exists, and then create it if it doesn't.

Using hasTable to make sure the table doesn't already exist is not strictly required since Dependencies could also be used to prevent any duplicate, but it can still be useful in case another sprinkle already created a table with the same name.

We then call a series of methods on the $table variable in create's closure, to set up the columns and other table properties.

You'll also notice that we've created a user_id column, which associates each record in members with a corresponding record in users. By adding a unique constraint to this column as well, we effectively set up a one-to-one relationship between members and users. Since we've also added a foreign key from user_id to the id column in users, it's very important that the two columns have the exact same type. Since id is an unsigned integer, user_id must also be defined as an unsigned integer.

For a complete explanation of the available methods for working with tables, see Laravel's Migrations chapter. They have a nice table with all the available options.

As for the down method, it simply tells the database structure to delete the table created by the up method when rolling back that migration. In the members example, the table created by the up method would be deleted by the down method.

For your table to work correctly with Eloquent, it should always have an autoincrementing id column which serves as the primary key. This is done automatically for you with the increments method.

Dependencies

An important aspect of migrations is data consistency. Since migrations are like recipes used to create a database, the order in which theses migrations are executed is very important. You don't want to drop those cupcakes in the oven before mixing the flour and eggs, the same way you don't want to add a column to a table before said table is created! UserFrosting uses dependencies to make sure migrations are run in the correct order.

Some situations require a more complex way to make sure migrations are run in the correct order. This is the case when a Sprinkle requires that a migration from another Sprinkle is executed before its own migration. It can also be the case when two tables inside the same Sprinkle are dependent on one another.

To define which migrations are required to be executed before your own migration, you can specify the fully qualified class name of the dependent migration as an array in the $dependencies attribute. For example:

<?php

namespace UserFrosting\Sprinkle\MySprinkle\Database\Migrations\v400;

use Illuminate\Database\Schema\Blueprint;
use Illuminate\Database\Schema\Builder;
use UserFrosting\Sprinkle\Core\Database\Migration;

class MembersTable extends Migration
{
    public static $dependencies = [
        '\UserFrosting\Sprinkle\Account\Database\Migrations\v400\UsersTable',
        '\UserFrosting\Sprinkle\Account\Database\Migrations\v400\RolesTable',
        '\UserFrosting\Sprinkle\Account\Database\Migrations\v400\RoleUsersTable'
    ];

    public function up()
    { ... }
}

The above example tells the bakery migrate command that the UsersTable, RolesTable and RoleUsersTable migrations from the Account Sprinkle need to be already executed before executing the MembersTable migration from the MySprinkle sprinkle. If those migrations are not yet executed and are pending execution, the migrate command will take care of the order automatically. If a migration's dependencies cannot be met, the migrate command will abort.

Dependencies can also target previous versions of your own migrations. For example, you should check that your member table is created before adding a new column in a new migration.

Running your migration

To run your migrations simply re-run the Bakery migrate from your command line, in UserFrosting's root directory:

$ php bakery migrate

If you want to do a "fresh install" of your migration or cancel the changes made, you can rollback the previous migration. You can also do a dry run of your migrations using the pretend option. See Chapter 8 for more details.