Eloquent relationships explained (with examples)
March 28, 2021
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!
