Database: Migrations

• Introduction
• Generating Migrations
  • Squashing Migrations
• Migration Structure
• Running Migrations
  • Rolling Back Migrations
• Tables
  • Creating Tables
  • Renaming / Dropping Tables
• Columns
  • Creating Columns
  • Column Modifiers
  • Modifying Columns
  • Dropping Columns
• Indexes
  • Creating Indexes
  • Renaming Indexes
  • Dropping Indexes
  • Foreign Key Constraints

Introduction

Migrations are like version control for your database, allowing your team to modify and share the application's database schema. Migrations are typically paired with Laravel's schema builder to build your application's database schema. If you have ever had to tell a teammate to manually add a column to their local database schema, you've faced the problem that database migrations solve.

The Laravel Schema facade provides database agnostic support for creating and manipulating tables across all of Laravel's supported database systems.

Generating Migrations

To create a migration, use the make:migration Artisan command:

php artisan make:migration create_users_table

The new migration will be placed in your database/migrations directory. Each migration file name contains a timestamp, which allows Laravel to determine the order of the migrations.

{tip} Migration stubs may be customized using stub publishing

The --table and --create options may also be used to indicate the name of the table and whether or not the migration will be creating a new table. These options pre-fill the generated migration stub file with the specified table:

php artisan make:migration create_users_table --create=users

php artisan make:migration add_votes_to_users_table --table=users

If you would like to specify a custom output path for the generated migration, you may use the --path option when executing the make:migration command. The given path should be relative to your application's base path.

Squashing Migrations

As you build your application, you may accumulate more and more migrations over time. This can lead to your migration directory becoming bloated with potentially hundreds of migrations. If you would like, you may "squash" your migrations into a single SQL file. To get started, execute the schema:dump command:

php artisan schema:dump

// Dump the current database schema and prune all existing migrations...
php artisan schema:dump --prune

When you execute this command, Laravel will write a "schema" file to your database/schema directory. Now, when you attempt to migrate your database and no other migrations have been executed, Laravel will execute the schema file's SQL first. After executing the schema file's commands, Laravel will execute any remaining migrations that were not part of the schema dump.

You should commit your database schema file to source control so that other new developers on your team may quickly create your application's initial database structure.

{note} Migration squashing is only available for the MySQL, PostgreSQL, and SQLite databases. However, database dumps may not be restored to in-memory SQLite databases.

Migration Structure

A migration class 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 reverse the operations performed by the up method.

Within both of these methods you may use the Laravel schema builder to expressively create and modify tables. To learn about all of the methods available on the Schema builder, check out its documentation. For example, the following migration creates a flights table:

<?php

use Illuminate\Database\Migrations\Migration;
use Illuminate\Database\Schema\Blueprint;
use Illuminate\Support\Facades\Schema;

class CreateFlightsTable extends Migration
{
    /**
     * Run the migrations.
     *
     * @return void
     */
    public function up()
    {
        Schema::create('flights', function (Blueprint $table) {
            $table->id();
            $table->string('name');
            $table->string('airline');
            $table->timestamps();
        });
    }

    /**
     * Reverse the migrations.
     *
     * @return void
     */
    public function down()
    {
        Schema::drop('flights');
    }
}

Running Migrations

To run all of your outstanding migrations, execute the migrate Artisan command:

php artisan migrate

{note} If you are using the Homestead virtual machine, you should run this command from within your virtual machine.

Forcing Migrations To Run In Production

Some migration operations are destructive, which means they may cause you to lose data. In order to protect you from running these commands against your production database, you will be prompted for confirmation before the commands are executed. To force the commands to run without a prompt, use the --force flag:

php artisan migrate --force

Rolling Back Migrations

To roll back the latest migration operation, you may use the rollback command. This command rolls back the last "batch" of migrations, which may include multiple migration files:

php artisan migrate:rollback

You may roll back a limited number of migrations by providing the step option to the rollback command. For example, the following command will roll back the last five migrations:

php artisan migrate:rollback --step=5

The migrate:reset command will roll back all of your application's migrations:

php artisan migrate:reset

Roll Back & Migrate Using A Single Command

The migrate:refresh command will roll back all of your migrations and then execute the migrate command. This command effectively re-creates your entire database:

php artisan migrate:refresh

// Refresh the database and run all database seeds...
php artisan migrate:refresh --seed

You may roll back & re-migrate a limited number of migrations by providing the step option to the refresh command. For example, the following command will roll back & re-migrate the last five migrations:

php artisan migrate:refresh --step=5

Drop All Tables & Migrate

The migrate:fresh command will drop all tables from the database and then execute the migrate command:

php artisan migrate:fresh

php artisan migrate:fresh --seed

{note} The migrate:fresh command will drop all database tables regardless of their prefix. This command should be used with caution when developing on a database that is shared with other applications.

Tables

Creating Tables

To create a new database table, use the create method on the Schema facade. The create method accepts two arguments: the first is the name of the table, while the second is a Closure which receives a Blueprint object that may be used to define the new table:

Schema::create('users', function (Blueprint $table) {
    $table->id();
});

When creating the table, you may use any of the schema builder's column methods to define the table's columns.

Checking For Table / Column Existence

You may check for the existence of a table or column using the hasTable and hasColumn methods:

if (Schema::hasTable('users')) {
    //
}

if (Schema::hasColumn('users', 'email')) {
    //
}

Database Connection & Table Options

If you want to perform a schema operation on a database connection that is not your default connection, use the connection method:

Schema::connection('foo')->create('users', function (Blueprint $table) {
    $table->id();
});

You may use the following commands on the schema builder to define the table's options:

Renaming / Dropping Tables

To rename an existing database table, use the rename method:

Schema::rename($from, $to);

To drop an existing table, you may use the drop or dropIfExists methods:

Schema::drop('users');

Schema::dropIfExists('users');

Renaming Tables With Foreign Keys

Before renaming a table, you should verify that any foreign key constraints on the table have an explicit name in your migration files instead of letting Laravel assign a convention based name. Otherwise, the foreign key constraint name will refer to the old table name.

Columns

Creating Columns

The table method on the Schema facade may be used to update existing tables. Like the create method, the table method accepts two arguments: the name of the table and a Closure that receives a Blueprint instance you may use to add columns to the table:

Schema::table('users', function (Blueprint $table) {
    $table->string('email');
});

Available Column Types

The schema builder contains a variety of column types that you may specify when building your tables:

Column Modifiers

In addition to the column types listed above, there are several column "modifiers" you may use while adding a column to a database table. For example, to make the column "nullable", you may use the nullable method:

Schema::table('users', function (Blueprint $table) {
    $table->string('email')->nullable();
});

The following list contains all available column modifiers. This list does not include the index modifiers:

Default Expressions

The default modifier accepts a value or an \Illuminate\Database\Query\Expression instance. Using an Expression instance will prevent wrapping the value in quotes and allow you to use database specific functions. One situation where this is particularly useful is when you need to assign default values to JSON columns:

<?php

use Illuminate\Support\Facades\Schema;
use Illuminate\Database\Schema\Blueprint;
use Illuminate\Database\Query\Expression;
use Illuminate\Database\Migrations\Migration;

class CreateFlightsTable extends Migration
{
    /**
     * Run the migrations.
     *
     * @return void
     */
    public function up()
    {
        Schema::create('flights', function (Blueprint $table) {
            $table->id();
            $table->json('movies')->default(new Expression('(JSON_ARRAY())'));
            $table->timestamps();
        });
    }
}

{note} Support for default expressions depends on your database driver, database version, and the field type. Please refer to the appropriate documentation for compatibility. Also note that using database specific functions may tightly couple you to a specific driver.

Modifying Columns

Prerequisites

Before modifying a column, be sure to add the doctrine/dbal dependency to your composer.json file. The Doctrine DBAL library is used to determine the current state of the column and create the SQL queries needed to make the required adjustments:

composer require doctrine/dbal

Updating Column Attributes

The change method allows you to modify type and attributes of existing columns. For example, you may wish to increase the size of a string column. To see the change method in action, let's increase the size of the name column from 25 to 50:

Schema::table('users', function (Blueprint $table) {
    $table->string('name', 50)->change();
});

We could also modify a column to be nullable:

Schema::table('users', function (Blueprint $table) {
    $table->string('name', 50)->nullable()->change();
});

{note} Only the following column types can be "changed": bigInteger, binary, boolean, date, dateTime, dateTimeTz, decimal, integer, json, longText, mediumText, smallInteger, string, text, time, unsignedBigInteger, unsignedInteger, unsignedSmallInteger and uuid.

Renaming Columns

To rename a column, you may use the renameColumn method on the schema builder. Before renaming a column, be sure to add the doctrine/dbal dependency to your composer.json file:

Schema::table('users', function (Blueprint $table) {
    $table->renameColumn('from', 'to');
});

{note} Renaming an enum column is not currently supported.

Dropping Columns

To drop a column, use the dropColumn method on the schema builder. Before dropping columns from a SQLite database, you will need to add the doctrine/dbal dependency to your composer.json file and run the composer update command in your terminal to install the library:

Schema::table('users', function (Blueprint $table) {
    $table->dropColumn('votes');
});

You may drop multiple columns from a table by passing an array of column names to the dropColumn method:

Schema::table('users', function (Blueprint $table) {
    $table->dropColumn(['votes', 'avatar', 'location']);
});

{note} Dropping or modifying multiple columns within a single migration while using a SQLite database is not supported.

Available Command Aliases

Indexes

Creating Indexes

The Laravel schema builder supports several types of indexes. The following example creates a new email column and specifies that its values should be unique. To create the index, we can chain the unique method onto the column definition:

$table->string('email')->unique();

Alternatively, you may create the index after defining the column. For example:

$table->unique('email');

You may even pass an array of columns to an index method to create a compound (or composite) index:

$table->index(['account_id', 'created_at']);

Laravel will automatically generate an index name based on the table, column names, and the index type, but you may pass a second argument to the method to specify the index name yourself:

$table->unique('email', 'unique_email');

Available Index Types

Each index method accepts an optional second argument to specify the name of the index. If omitted, the name will be derived from the names of the table and column(s) used for the index, as well as the index type.

Index Lengths & MySQL / MariaDB

Laravel uses the utf8mb4 character set by default, which includes support for storing "emojis" in the database. If you are running a version of MySQL older than the 5.7.7 release or MariaDB older than the 10.2.2 release, you may need to manually configure the default string length generated by migrations in order for MySQL to create indexes for them. You may configure this by calling the Schema::defaultStringLength method within your AppServiceProvider:

use Illuminate\Support\Facades\Schema;

/**
 * Bootstrap any application services.
 *
 * @return void
 */
public function boot()
{
    Schema::defaultStringLength(191);
}

Alternatively, you may enable the innodb_large_prefix option for your database. Refer to your database's documentation for instructions on how to properly enable this option.

Renaming Indexes

To rename an index, you may use the renameIndex method. This method accepts the current index name as its first argument and the desired new name as its second argument:

$table->renameIndex('from', 'to')

Dropping Indexes

To drop an index, you must specify the index's name. By default, Laravel automatically assigns an index name based on the table name, the name of the indexed column, and the index type. Here are some examples:

If you pass an array of columns into a method that drops indexes, the conventional index name will be generated based on the table name, columns and key type:

Schema::table('geo', function (Blueprint $table) {
    $table->dropIndex(['state']); // Drops index 'geo_state_index'
});

Foreign Key Constraints

Laravel also provides support for creating foreign key constraints, which are used to force referential integrity at the database level. For example, let's define a user_id column on the posts table that references the id column on a users table:

Schema::table('posts', function (Blueprint $table) {
    $table->unsignedBigInteger('user_id');

    $table->foreign('user_id')->references('id')->on('users');
});

Since this syntax is rather verbose, Laravel provides additional, terser methods that use convention to provide a better developer experience. The example above could be written like so:

Schema::table('posts', function (Blueprint $table) {
    $table->foreignId('user_id')->constrained();
});

The foreignId method is an alias for unsignedBigInteger while the constrained method will use convention to determine the table and column name being referenced. If your table name does not match the convention, you may specify the table name by passing it as an argument to the constrained method:

Schema::table('posts', function (Blueprint $table) {
    $table->foreignId('user_id')->constrained('users');
});

You may also specify the desired action for the "on delete" and "on update" properties of the constraint:

$table->foreignId('user_id')
      ->constrained()
      ->onUpdate('cascade')
      ->onDelete('cascade');

Any additional column modifiers must be called before constrained:

$table->foreignId('user_id')
      ->nullable()
      ->constrained();

To drop a foreign key, you may use the dropForeign method, passing the foreign key constraint to be deleted as an argument. Foreign key constraints use the same naming convention as indexes, based on the table name and the columns in the constraint, followed by a "_foreign" suffix:

$table->dropForeign('posts_user_id_foreign');

Alternatively, you may pass an array containing the column name that holds the foreign key to the dropForeign method. The array will be automatically converted using the constraint name convention used by Laravel's schema builder:

$table->dropForeign(['user_id']);

You may enable or disable foreign key constraints within your migrations by using the following methods:

Schema::enableForeignKeyConstraints();

Schema::disableForeignKeyConstraints();

{note} SQLite disables foreign key constraints by default. When using SQLite, make sure to enable foreign key support in your database configuration before attempting to create them in your migrations. In addition, SQLite only supports foreign keys upon creation of the table and not when tables are altered.