How to Use Laravel Many To Many Relationship

In Laravel, eloquent relationships are defined as methods on your Eloquent model classes and are very robust query builders. Eloquent makes managing and working with these relationships effortless and helps a variety of common relationships.

Laravel many to many

Laravel Many-to-many relationships are defined by writing a method that returns the result of the belongsToMany. Many to many relationship is slightly more complicated than hasOne and hasMany relationships.

The join (or pivot) table is the key to the many-to-many relationship. The pivot table allows the relationship id from one model to be related to many other models and vice-versa.

In our example, we will define the two models.

1. Category
2. Product

In our example, Multiple Categories have Multiple Products, and an inverse relationship will be Multiple Products belongs to Multiple Categories.

So, what we can do is that when we go to a particular category, we need to display all the Products.

Same, when we see a particular Product, we need to display all the Categories that belong to that specific Product.

We start this practical example by installing the Laravel project.

Step 1: Install Laravel.

I am using Laravel Valet to create a new project using the following command.

laravel new relationships

If you are not using Laravel Valet, install it using the following command.

composer create-project laravel/laravel relationship --prefer-dist

Go into the project.

cd relationships

Open the project in your editor.

code .

First thing, set up the database.

Step 2: Create a model and migration.

We are defining two models for our example.

1. Category
2. Product

php artisan make:model Category -m
php artisan make:model Product -m

It will create products and categories, tables, and models.

Now, inside create_categories_table, define the following schema.

// create_categories_table

/**
     * Run the migrations.
     *
     * @return void
     */
    public function up()
    {
        Schema::create('categories', function (Blueprint $table) {
            $table->increments('id');
            $table->string('title');
            $table->timestamps();
        });
    }

Also, write the following schema inside the create_products_table.

// create_products_table

   /**
     * Run the migrations.
     *
     * @return void
     */
    public function up()
    {
        Schema::create('products', function (Blueprint $table) {
            $table->increments('id');
            $table->string('name');
            $table->float('price');
            $table->timestamps();
        });
    }

Now, go to the terminal and create the tables using the following command.

php artisan migrate

Step 3: Define random categories manually.

In this example, we are just focusing on how many to many relationship works and how we can assign the values and create a relationship with one to another table. So, we make three categories manually inside the database table.

So, we have manually defined three categories.

Step 4: Define a Pivot table.

Many-to-many relations require an intermediary table to manage the relationship.

The most straightforward implementation of the intermediary table, known as a pivot table, would consist of just two columns for storing the foreign keys pointing to each related pair of records.

How to create a Pivot table in Laravel

1. The name of the pivot table should consist of singular names of both tables, separated by underscore symbols, and these names should be arranged in alphabetical order, so we have to have category_product, not product_category.
2. To create a pivot table, we can create the simple migration with artisan make:migration or use the community package Laravel 5 Generators Extended. For example, we have the command artisan make:migration:pivot.
3. Pivot table fields: by default, there should be only two fields – the foreign key to each table, in our case category_id and product_id. You can insert more fields if you need, then you need to add them to the relationship assignment.

Let’s use the above rules in our example.

So, we have already defined two table schemas 1) Category 2) Product.

Now, we need to define the third table, which is the Pivot table. 

The Pivot table is the relationship between two tables.

So the Pivot table has these columns.

1. id
2. category_id
3. product_id

Now, we are creating Many to Many relationships; that is why many products have categories. For example, to create a migration file, type the following command.

php artisan make:migration create_category_product_table --create=category_product

Now, define the following schema in the migration file.

// create_category_product_table

/**
     * Run the migrations.
     *
     * @return void
     */
    public function up()
    {
        Schema::create('category_product', function (Blueprint $table) {
            $table->increments('id');
            $table->integer('category_id')->unsigned();
            $table->integer('product_id')->unsigned();
        });
    }

Now, migrate using the following command.

php artisan migrate

Step 5: Define Many To Many relationships.

Multiple Categories belong to Multiple Products. So inside the Product.php file, we can define the belongsToMany relationship.

// Product.php

<?php

namespace App;

use Illuminate\Database\Eloquent\Model;

class Product extends Model
{
    public function categories()
    {
        return $this->belongsToMany(Category::class);
    }
}

Also, the same for the products. Multiple Products belong To Multiple Categories. So inside the Category.php file, we can define the belongsToMany relationship.

// Category.php

<?php

namespace App;

use Illuminate\Database\Eloquent\Model;
use App\Product;

class Category extends Model
{
    public function products()
    {
        return $this->belongsToMany(Product::class);
    }
}

So, we have defined the relationship between them.

Now, let us create a new product and assign the category to the Product.

Step 6: Create a Product.

In a real-time scenario, we create a form, and then through a POST request, we insert the Product data into the table.

However, in this example, we will not define any form; we directly store the data in the database because our goal is to use many to many relationships to the complex scenario.

Now, define a route that saves the Product into the database and assigns the Product to the category using many to many relationships.

Now, we have four(4) categories. So, we create a product and assign the two categories to one Product.

First, create a ProductController using the following command.

php artisan make:controller ProductController

The next step, define the route to store the Product.

Now, I am using a GET request for saving the data because we have not created the form, so we take every data manually.

// ProductController.php

Route::get('product/create', 'ProductController@create')->name('product.create');

Import both models in this ProductController.php file.

Also, Now, what we are going to do is we will create one Product that belongs To Many Categories.

In this example tutorial, we will create a God of War product.

Now, the God of War belongs to two categories.

1. Video Games
2. Playstation

So, when we create a product, we also need to fill the pivot table with the two categories.

So, our product_id will be one, but the category_id will be different, creating two rows in the category_product table.

Now, write the following code inside ProductController’s create() function.

// ProductController.php

<?php

namespace App\Http\Controllers;
use App\Category;
use App\Product;

use Illuminate\Http\Request;

class ProductController extends Controller
{
    public function create(Request $request)
    {
        $product = new Product;
        $product->name = 'God of War';
        $product->price = 40;

        $product->save();

        $category = Category::find([3, 4]);
        $product->categories()->attach($category);

        return 'Success';
    }
}

Explanation.

First, we created the Product and saved it in the products table.

Now, it is time to assign the categories to the newly created Product.

Since we need an ID of categories, so right now, I have coded manually, but in real-time, you have those ids in the form request.

The attach() function will now assign those category ids to the newly created Product and create two new rows inside the pivot table. Each row has a relationship with its Product and category.

The next step is going to this URL: http://relationships.test/product/create or http://localhost:8000/product/create

You can see the “Success.”

Now, go to the database and see the products table.

Also, you can check the Pivot Table, a create_product table.

If we have done it all correctly, we can see the two rows inside the table, where product_id is the same 1 for both the rows, but category_id’s are different, which are 3 and 4.

Yayy!!, we have successfully attached the two categories to one Product.

The next step is to display the Product Information and all the Categories inside that Product.

Step 7: Display Product Information.

Define the route that can display all the information.

// web.php

Route::get('product/{product}', 'ProductController@show')->name('product.show');

Now, define the ProductController’s show function.

In this function, I am using Routing Model Binding.

// ProductController.php

public function show(Product $product)
{
   return view('product.show', compact('product'));
}

We pass the product id in the get request, fetch the product details via Route Model Binding directly, and give that product detail to the view.

Create a new folder inside the views folder called products and inside that, create one file called show.blade.php.

Write the following code inside the show.blade.php file. We display the product name, price, and belongs to categories.

// show.blade.php

<h2>Product Name: </h2>
<p>{{ $product->name }} || ${{ money_format($product->price, 2) }}</p>

<h3>Product Belongs to</h3>

<ul>
    @foreach($product->categories as $category)
    <li>{{ $category->title }}</li>
    @endforeach
</ul>

As we have defined the relationship, we can directly fetch all the categories from the Product model, which is the magic of Eloquent Relationships in Laravel.

Now, go to this URL: http://relationships.test/product/1 or http://localhost:8000/product/1

As you can see, we have only one Product created to see only one product detail.

So, this is how you can add multiple categories to a product and display multiple categories for a product.

Now, you can create as many products as you want and assign multiple categories to them.

You can also delete the relationship between the tables using the detach() function.

Detach() function.

// ProductController.php

public function removeCategory(Product $product)
{
        $category = Category::find(3);

        $product->categories()->detach($category);
        
        return 'Success';
}

Now, define the following route inside a web.php file.

// web.php

Route::get('category/product/{product}', 'ProductController@removeCategory')->name('category.product.delete');

Next, type this URL: http://relationships.test/category/product/1 or http://localhost:8000/category/product/1.

Hit enter, and we get success now. Go to the MySQL database and check the category_product table.

You can see that the category_id = 3 row is deleted, and we no longer belong to category_id = 3.

So, this is how you can maintain many-to-many relationships in Laravel.

Conclusion

Laravel Many To Many Relationship relates a record on the table to one or many records in another table and vice versa. Unlike Laravel One to Many and One to One, the key is a pivot table in this relationship.

The pivot table is a table where you define between two tables to link them. A pivot table allows the relationship id from one model to be related to many other models and vice-versa.

One real-life example we can think of is products and categories. A category can have many products, and a product can relate to many categories; simple isn’t.

That’s it for this many-to-many relationship tutorial.

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