Eloquent relationships explained (with examples)

In my opinion, Eloquent is one of the most powerful features of Laravel. It is an API for interacting with your database, and it has a very nice and easy-to-remember syntax. For example:

$post->author->name; 

Will give you the name of the post's author.

This is an example of an Eloquent relationship. Relationships define how your models (tables) are connected. Although most are easy to understand, there are a few more complicated ones.

In this post, I'm going to show how every relationship works.

One to one (has one)

For this example, we have two models: a User and an Address. The User model holds information such as name, email address, and password, and the Address model holds information like country, state, city, etc.

• A User has one Address
• An Address belongs to a User

We may have this table structure:

users id - integer name - string email - string password - string address id - integer country - string city - string user_id - integer 

You can define these relationships like this:

// app/Models/User.php public function address() { return $this->hasOne(Address::class); } 

Now you can access the user's address using $user->address->city.

Note: for this to work, the Address model should have a user_id column.

Inverse (belongs to)

If you have an Address and want to find the corresponding User, then define this relationship:

// app/Models/Address.php public function user() { return $this->belongsTo(User::class); } 

One to many (has many)

In this example, we have two models: a Post and a Category.

• A Post belongs to a Category
• A Category has many Posts

And we have this table structure:

categories id - integer name - string posts id - integer title - string category_id - integer 

We can define this relationship like this:

// app/Models/Category.php public function posts() { return $this->hasMany(Post::class); } 

And you can access all the posts like this:

foreach($category->posts as $post) { // } 

Note: for this to work, the Post model should have a category_id column.

Many to one (belongs to)

In this example, we have two models: a Post and a Category.

• A Post belongs to a Category
• A Category has many Posts

And we have this table structure:

categories id - integer name - string posts id - integer title - string category_id - integer 

We can define this relationship like this:

// app/Models/Post.php public function category() { return $this->belongsTo(Category::class); } 

And you can access the Post's category like this:

$post->category->name; 

Has many through

This relationship is a bit more difficult. In this example, we have three models: an Author, a Post, and a Language.

• A Post belongs to an Author
• An Author has many Posts
• An Author "belongs" to a Language (speaks a language)
• A Language has many Authors

For example, this is our table structure:

languages id - integer name - string authors id - integer name - string language_id - integer posts id - integer title - string author_id - integer 

If we want to get all posts in a specific language, we can define this relationship:

// app/Models/Language.php public function posts() { return $this->hasManyThrough(Post::class, User::class); } 

Now, we can get all posts using:

foreach($language->posts as $post) { // } 

Inverse

If you now want to get the Language of a Post, you can just simply do this:

$post->user->language->name; 

Many to many (belongs to many)

In this example, we have two models: a Product and a Tag.

• A Product has many Tags
• A Tag has many Products

And we may have this table structure:

products id - integer name - string price - integer tags id - integer name - string product_tag product_id - integer tag_id - integer 

Note: in the table structure, we have a third table, product_tag. This table connects products to tags.

Now we can define the relationships like this:

// app/Models/Product.php public function tags() { return $this->belongsToMany(Tag::class); } 

// app/Models/Tag.php public function products() { return $this->belongsToMany(Product::class); } 

Now we can get all tags/products using:

foreach($product->tags as $tag) { // } 

foreach($tag->products as $product) { // } 

In the next post, I'm going to show what polymorphic relationships are and how to use them. Thanks for reading!