How to create foreign key constraints in Laravel

• 23 Mar 2020
• |
2 comments

In Laravel we can define relationships between two tables using the foreign key and used to link them. It refers to the primary key of the main table. The main table is called the parent table and another table which have a primary key and foreign key is called the child table. In Laravel If the foreign key's onDelete clause is defined, the database should delete the users if the user is deleted.

It will clear with below example, in which create two tables users and posts. 

First run these two commands to create a migration

php artisan make:migration create_users_table --create=users
php artisan make:migration create_posts_table --create=posts

Two migration files were created under laravelApp/database/migrations. Open these files and replace them with below code.

users table migration

<?php
use Illuminate\Support\Facades\Schema;
use Illuminate\Database\Schema\Blueprint;
use Illuminate\Database\Migrations\Migration;

class CreateUsersTable extends Migration
{
    /**
     * Run the migrations.
     *
     * @return void
     */
    public function up()
    {
        Schema::create('users', function (Blueprint $table) {
            $table->bigIncrements('id');
            $table->string('name');
            $table->string('email')->unique();
            $table->timestamp('email_verified_at')->nullable();
            $table->string('password');
            $table->rememberToken();
            $table->timestamps();
        });
    }
    /**
     * Reverse the migrations.
     *
     * @return void
     */
    public function down()
    {
        Schema::dropIfExists('users');
    }
}

posts table migration

<?php
use Illuminate\Support\Facades\Schema;
use Illuminate\Database\Schema\Blueprint;
use Illuminate\Database\Migrations\Migration;

class CreatePostsTable extends Migration
{
    /**
     * Run the migrations.
     *
     * @return void
     */
    public function up()
    {
        Schema::create('posts', function (Blueprint $table) {
            $table->bigIncrements('id');
			$table->string('title')->unique();
			$table->longText('content')->nullable();
			$table->string('image')->nullable();
			$table->unsignedBigInteger('created_by');
			$table->foreign(''created_by'')->references('id')->on('users')->onDelete('cascade');
			$table->timestamps();
        });
    }

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

After that run command `php artisan migrate`. Tables were created in your database `users` and `posts`. Posts table data will delete if a user row is deleted.

php artisan make:migration create_users_table --create=users
php artisan make:migration create_posts_table --create=posts

<?php
use Illuminate\Support\Facades\Schema;
use Illuminate\Database\Schema\Blueprint;
use Illuminate\Database\Migrations\Migration;

class CreateUsersTable extends Migration
{
    /**
     * Run the migrations.
     *
     * @return void
     */
    public function up()
    {
        Schema::create('users', function (Blueprint $table) {
            $table->bigIncrements('id');
            $table->string('name');
            $table->string('email')->unique();
            $table->timestamp('email_verified_at')->nullable();
            $table->string('password');
            $table->rememberToken();
            $table->timestamps();
        });
    }
    /**
     * Reverse the migrations.
     *
     * @return void
     */
    public function down()
    {
        Schema::dropIfExists('users');
    }
}

<?php
use Illuminate\Support\Facades\Schema;
use Illuminate\Database\Schema\Blueprint;
use Illuminate\Database\Migrations\Migration;

class CreatePostsTable extends Migration
{
    /**
     * Run the migrations.
     *
     * @return void
     */
    public function up()
    {
        Schema::create('posts', function (Blueprint $table) {
            $table->bigIncrements('id');
			$table->string('title')->unique();
			$table->longText('content')->nullable();
			$table->string('image')->nullable();
			$table->unsignedBigInteger('created_by');
			$table->foreign(''created_by'')->references('id')->on('users')->onDelete('cascade');
			$table->timestamps();
        });
    }

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