Your First Eloquent Relationship in Laravel

Ep#24@Laracasts: Your First Eloquent Relationship

This post is a part of the Week X of 100DaysOfCode Laravel Challenge series.

Our next goal is to assign a category to our blog posts in our Blog Project. We show the category name on the blog archive and single post pages under post title.

We already have a posts table for our posts. Now we will need another table for categories. We can make a relationship between the two tables so that each post entry has the category id it is assigned to.

So, we need to generate a migration and a model for the Category. We can generate them in two separate commands

php artisan make:model Category
php artisan make:migration categories

or in one single command

php artisan make:model Category -m

where the -m flag in the command is meant for a migration along with the model.

Now add the fields title and slug to the category schema in the categories migration. And add the category_id as foreign key $table->foreignId("category_id"); to the posts migration. Run your migrations php artisan migrate:fresh. Boot up tinker php artisan tinker and add some records to your categories table.

use App\Models\Category;

$c = new Category;
$c->title = "Personal";
$c->slug = "personal";
$c->save();

Repeat the above commands for two other categories Work and Hobbies.

As we have assigned an empty array to the $guarded property in our Post model, we can create posts using Mass Assignment.

use App\Models\Post;

$post = new Post;
$post->create(["title" => "Just a personal post", "slug" => "just-a-personal-post", "excerpt" => "lorem ipsum is simply....", "body" => "Lorem ipsum is simply a dummy text...", "category_id" => 1]);

Similarly, create some posts for the Work and Hobbies categories by assigning the respective category ids to them.

Now that we have assigned a category id to every post, can we access the category of a post like $post->category? Nope, not yet, because we have not added Eloquent Relationship to our Post model yet. The $post->category will return null instead.

In the Post model, add a method category() and return the appropriate relationship.

public function category() {
        return $this->belongsTo(Category::class);
}

We used the belongsTo() relation because in our case a category can have many posts but a post is assigned to exactly one category.

How to access a related model?

Now that we have added the Category relation to our Post model, it is time access the related category of a post. A potential confusion here could be trying to access the related model as a method $post->category(), which will return the relation Illuminate\Database\Eloquent\Relations\BelongsTo {#4351} instead of the model instance App\Models\Category. So, access it as a property instead of a method.

use App\Models\Post;

$post = Post::first();
$post->category;

And it will return the category model instance as

>>> $post->category;
=> App\Models\Category {#3560
     id: 1,
     title: "Personal",
     slug: "personal",
     created_at: "2021-12-15 16:44:33",
     updated_at: "2021-12-15 16:44:33",
   }
>>>

Now you can access the related category title $post->category->title which will return Personal in the above case.

Update your blade templates to show a the associated category under each post title.

<p><a href="#">{{ $post->category->title }}</a></p>

Here we are introducing a problem called the N+1 problem which we will discuss in another episode. Now visit your blog listing page and you will see the category under post title as