Implicitly Binding Multiple Eloquent Models in Laravel Route Definitions

web-application-framework laravel

In this post, I explored how to implicitly bind multiple Eloquent models in a Laravel route definition.

References

Prerequisites

Using MySQL as the database for the Laravel project.
For information on how to interact with MySQL from a Laravel project, refer to this guide.

Environment

Laravel 11
mysql 8.0.34 for Linux

Create Database Tables and Eloquent Models
Insert Data into Database Tables
Define Routes and Verify Functionality

1. Create Database Tables and Eloquent Models

Create two database tables and Eloquent models: users and comments.

The comments table is a child of the users table.
The child table should have a column indicating the parent table’s id, typically named <parent_table_name_without_s>_id.
In this case, the comments table will have a user_id column.

Run the following commands to create the Eloquent models and migrations:

php artisan make:model User -m    # Skip if the 'users' table already exists
php artisan make:model Comment -m

Open the migration file database/migrations/*_create_comments_table.php and add the user_id column in the up method:

*_create_comments_table.php :

public function up(): void
{
    Schema::create('comments', function (Blueprint $table) {
        $table->id();
        $table->integer('user_id'); // Added
        $table->timestamps();
    });
}

In the app/Models/User.php file, add a method to retrieve the user’s comments. The method name should match the plural form of the child table’s name:

User.php :

public function comments(): HasMany
{
    return $this->hasMany(Comment::class);
}

2. Insert Data into Database Tables

Insert data into the users and comments tables.

For the comments table, set the user_id column to correspond to the id values in the users table:

mysql> select * from users;
+----+-     -+---------------------+---------------------+
| id |       | created_at          | updated_at          |
+----+- ... -+---------------------+---------------------+
|  1 |       | 2024-05-08 07:23:50 | 2024-05-08 07:23:50 |
|  2 |       | 2024-05-08 07:24:06 | 2024-05-08 07:24:06 |
+----+-     -+---------------------+---------------------+

mysql> select * from comments;
+----+---------+---------------------+---------------------+
| id | user_id | created_at          | updated_at          |
+----+---------+---------------------+---------------------+
|  1 |       1 | 2024-05-08 07:24:34 | 2024-05-08 07:24:34 |
|  2 |       1 | 2024-05-08 07:24:42 | 2024-05-08 07:24:42 |
|  3 |       2 | 2024-05-08 07:24:49 | 2024-05-08 07:24:49 |
+----+---------+---------------------+---------------------+

3. Define Routes and Verify Functionality

Define a route that implicitly binds multiple Eloquent models:

For this example, add the following to routes/web.php.

web.php :

Route::get('/users/{user}/comments/{comment}', function (User $user, Comment $comment) {
    return $comment;
})->scopeBindings();

Call the scopeBindings method to implicitly bind multiple Eloquent models. Access http://localhost:8080/users/1/comments/1 in your browser.

You can get a comment model with user_id column is 1 and id column is 1.

{"id":1,"user_id":1,"created_at":"2024-05-08T07:24:34.000000Z","updated_at":"2024-05-08T07:24:34.000000Z"}

If you try to access a comment that doesn’t belong to the specified user: http://localhost:8080/users/1/comments/3

You will receive a 404 error, indicating that a comment model with user_id equal to 1 and id equal to 3 does not exist.

About the scopeBindings Method

Without calling the scopeBindings method, Laravel would attempt to bind the comment model independently, without considering its relationship to the user model.

In the above example, if you access /users/1/comments/3 not calling scopeBindings, you get a user model with id column is 1 and a comment model with id column is 3, which means that Laravel doesn’t consider their relationship as the user doesn’t have the comment with id equal to 3.
Calling scopeBindings, Laravel doesn’t retrieve those models and displays a 404 error page instead.

However, as mentioned in the later section, when retrieving data using a column other than id, there is no need to call the scopeBindings method.

(Bonus) Binding Eloquent Models Using Columns Other Than id

By default, Laravel binds Eloquent models using the id column.
To perform implicit binding using a different column, make the following changes.

Add a comment_id column to the comments table and use it to retrieve data.
Modify the comments table and its data as shown below: