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This tutorial aims to guide you through the process of creating model instances and their related models using Laravel factories. Creating Models using factories is useful both for writing seeders as well as automated tests. In Laravel, you can create a model with related models. Create a single instance with a relation: Category::factory()->has(Post::factory())->create();, or generate multiple instances: Category::factory()->count(3)->has(Post::factory()->count(5))->create(); This guide will walk you through the process of building an example app with migrations, models, factories, and a seeder to fill the database with records and related records. Let's get started! Step 1: Create and Run Migrations Begin by creating migrations for both of your models' tables using the make:migration command: php artisan make:migration create_posts_table php artisan make:migration create_categories_table Edit the generated migration files to define the structure of both tables. For posts use: id(); $table->string('title'); $table->text('content'); $table->foreignId('category_id')->constrained(); $table->timestamps(); }); } /** * Reverse the migrations. */ public function down(): void { Schema::dropIfExists('posts'); } }; For categories use: id(); $table->string('name'); $table->timestamps(); }); } /** * Reverse the migrations. */ public function down(): void { Schema::dropIfExists('categories'); } }; Then, run the migrations to create the tables: php artisan migrate Step 2: Create the Models Generate Eloquent models for both tables by using the make:model command: php artisan make:model Post php artisan make:model Category Step 3: Add the Model Code Now you'll need to define the relationships within your model classes. For the Post model, use: belongsTo(Category::class); } } For the Category model, use: hasMany(Post::class); } } Step 4: Creating Factories with Relations Now we'll create a factory for each model by running the following artisan commands: php artisan make:factory PostFactory --model=Post php artisan make:factory CategoryFactory --model=Category Now, let's add the factory code, which essentially defines how the column values of a model should be structured. I chose to use Faker to generate random content. This is useful for inserting arbitrary amounts of unique data into the database that resembles real information to some extent. For the PostFactory, use: */ public function definition(): array { return [ 'title' => $this->faker->sentence, 'content' => $this->faker->paragraph, ]; } } For the CategoryFactory, use: */ public function definition(): array { return [ 'name' => $this->faker->word, ]; } } Step 5: Make a Seeder and Populate Data To generate seeders that will seed records for both models we'll run make:seeder: php artisan make:seeder PostsAndCategoriesTableSeeder Now, edit the generated seeder file and add code to the run method. The run method of a seeder is typically where we use factories to create data, in this case, 3 categories, and for each of the categories 5 related posts: has(Post::factory()->count(5)) ->count(3) ->create(); } } Step 6: Run the Seeder to Generate Data With Relations Now let's run the seeder to populate the tables with test data, including relationships between models, by running: php artisan db:seed --class=PostsAndCategoriesTableSeeder Now, if we check our database, we can observe the generated data. Running our seeder resulted in the insertion of 3 categories and 15 posts (3 x 5 = 15) into the database. The Latin text was generated by Faker generating mock data. Result of Running Our Seeder to Generate Data for Categories and Related Posts When to Use ->for and When to Use ->has on a Factory Factories support both ->for and ->has when creating instances and relationships. Let's clarify when to use each method: Use ->has when: You want to create multiple related models for each instance of the main model. This is useful when each "Category" has multiple associated "Posts". For example: // Create a category and one associated post Category::factory()->has(Post::factory())->create(); // Create 3 categories, each with 5 associated posts Category::factory() ->count(3) ->has(Post::factory()->count(5)) ->create(); Use ->for when: You want to associate a single related model with each instance of the main model. For instance, when each Post belongs to a single Category. For example: // Create a category $category = Category::factory()->create(); // Create a post and associate it with the category we made $post = Post::factory()->for($category)->create(); // Create 5 posts and associate each with the category we made $category = Post::factory()->count(5)->for($category)->create(); Conclusion Laravel's features for creating model relationships, combined with factories and seeders, simplify the process of setting up your database with interconnected test data. By following the steps, you'll be able to seamlessly integrate relationships into your data generation, making testing and development more effective. Happy coding! References: Eloquent Relationships (Official Documentation) Factories (Official Documentation) Seeders (Official Documentation)

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