Many-to-many (belongsToMany) in Laravel - Mini Project: Build & Apply

Many-to-many Relationship with belongsToMany in Laravel

📖 Scenario: You are building a simple blog system where posts can have many tags, and tags can belong to many posts. This is a common real-world case where many items relate to many others.

🎯 Goal: Create a many-to-many relationship between Post and Tag models using Laravel's belongsToMany method. You will set up the data structure, configure the pivot table, define the relationship methods, and finally retrieve tags for a post.

📋 What You'll Learn

Create a pivot table migration named post_tag with post_id and tag_id columns

Define a tags method in the Post model using belongsToMany

Define a posts method in the Tag model using belongsToMany

Retrieve all tags for a given post using the tags relationship

💡 Why This Matters

🌍 Real World

Many web applications need to relate items in a many-to-many way, such as posts and tags, users and roles, or products and categories.

💼 Career

Understanding Laravel's many-to-many relationships is essential for backend developers working with databases and Eloquent ORM.

1

Create the pivot table migration

Create a migration file for the pivot table named post_tag with two unsigned big integer columns: post_id and tag_id. Use the Laravel schema builder to define these columns and set them as foreign keys referencing id on posts and tags tables respectively.

Laravel

// Your code here to create the post_tag pivot table migration
Schema::create('post_tag', function (Blueprint $table) {
    // Your code here
});

Need a hint?

Use Schema::create with a closure that receives $table. Add unsignedBigInteger columns for post_id and tag_id. Then add foreign key constraints referencing posts and tags tables.

2

Define the belongsToMany relationship in Post model

In the Post model, add a public method named tags that returns the result of calling belongsToMany(Tag::class). This sets up the many-to-many relationship from posts to tags.

Laravel

Schema::create('post_tag', function (Blueprint $table) {
    $table->unsignedBigInteger('post_id');
    $table->unsignedBigInteger('tag_id');
    $table->foreign('post_id')->references('id')->on('posts')->onDelete('cascade');
    $table->foreign('tag_id')->references('id')->on('tags')->onDelete('cascade');
    $table->primary(['post_id', 'tag_id']);
});

// Add the tags() method inside the Post model
// Your code here

Need a hint?

Inside the Post model class, define a public method tags that returns $this->belongsToMany(Tag::class).

3

Define the belongsToMany relationship in Tag model

In the Tag model, add a public method named posts that returns the result of calling belongsToMany(Post::class). This sets up the many-to-many relationship from tags to posts.

Laravel

Schema::create('post_tag', function (Blueprint $table) {
    $table->unsignedBigInteger('post_id');
    $table->unsignedBigInteger('tag_id');
    $table->foreign('post_id')->references('id')->on('posts')->onDelete('cascade');
    $table->foreign('tag_id')->references('id')->on('tags')->onDelete('cascade');
    $table->primary(['post_id', 'tag_id']);
});

class Post extends Model
{
    public function tags()
    {
        return $this->belongsToMany(Tag::class);
    }
}

// Add the posts() method inside the Tag model
// Your code here

Need a hint?

Inside the Tag model class, define a public method posts that returns $this->belongsToMany(Post::class).

4

Retrieve tags for a post

Write code to retrieve all tags for a Post instance stored in a variable named $post. Use the tags relationship method to get the collection of tags and assign it to a variable named $tags.

Laravel

Schema::create('post_tag', function (Blueprint $table) {
    $table->unsignedBigInteger('post_id');
    $table->unsignedBigInteger('tag_id');
    $table->foreign('post_id')->references('id')->on('posts')->onDelete('cascade');
    $table->foreign('tag_id')->references('id')->on('tags')->onDelete('cascade');
    $table->primary(['post_id', 'tag_id']);
});

class Post extends Model
{
    public function tags()
    {
        return $this->belongsToMany(Tag::class);
    }
}

class Tag extends Model
{
    public function posts()
    {
        return $this->belongsToMany(Post::class);
    }
}

// Assume $post is an instance of Post
$tags = null; // Your code here to get tags

Need a hint?

Use the tags property or method on the $post object to get all related tags and assign it to $tags.