CODEWITHSUNDEEP
ormlaravellaravel-4relationshipeloquent
preyz
preyz

Reputation: 3159

Many To Many relationships in Laravel: belongsToMany() vs. hasManyThrough()

What is the difference between using belongsToMany() or hasManyThrough() when defining a Many To Many relationship in Laravel?

Example: User Account Account_User

So, User has a many to many relation to Account via the Account_User table. On top of being just the pivot table that defines the related Users with related Accounts, it also stores a Account_User.role field, which determines which role a given user has in a given account.

What would the implications be of using either User belongsToMany() Account or User hasManyThrough() Account Account_User? Or is this essentially the same?

When decided upon a method, I guess I should use the same method for the reverse relation definition.

Upvotes: 27

Views: 11021

Answers (3)

Alex Vlas
Alex Vlas

Reputation: 53

I have struggled with this as well and came up with this solution in my head. A pivot table will have TWO keys to both entities it is related and it will be a belongsToMany. If the middle table only has connections to one entity then it is a hasManyThrough.

If I take all the examples given above:

Films, Categories there will be a middle table FilmCategories with TWO keys to both Categories and Films and therefor it will be a belongsToMany.

Company, Office, Employees in this case we have 3 tables probably office points to company and employee points to office. None of the 3 tables will have keys to the other 2 so its a hasManyThrough.

In the op's case there are 3 tables User, Account and Account_User. This is a belongsToMany because Account_User will have keys to both Account and User.

Hope that helps a bit of a repeat and old question but it did confuse me a lot as well.

Upvotes: 0

Maksim Ivanov
Maksim Ivanov

Reputation: 4311

While @Arda's answer is absolutely correct, I found myself needing some time to digest it. So here is my attempt to put the same thing in simpler terms.

hasManyThrough is useful when you have something similar to the following scenario:

  • A company has many offices and each office has many employees working in it. In other words, Company one-to-many Office, and Office one-to-many Employee. And if you want to fetch all employees working for a given company, you need:
// Company Model

public function employees()
{
    return $this->hasManyThrough('App\Employee', 'App\Office');
}

belongsToMany, on the other hand, is useful when you have a many-to-many relationship with a pivot table in-between. For example:

  • A film can have many categories (comedy, drama, etc.) and each category can belong to many films. In other words, Film many-to-many Category. And if you want to fetch all categories for a given film, you need:
// Film Model

public function categories()
{
    return $this->belongsToMany('App\Category', 'pivot_table_name');
}

Given the scenario in question, belongsToMany is the relationship needed to connect many Users to many Accounts. hasManyThrough cannot be applied.

Upvotes: 13

Arda
Arda

Reputation: 6926

Let's say you have two models, let's call A and B:

If A may have more than one items of B, and also If B may have more than one items of A (think like blog posts / tags) You have to use belongsToMany();

Now let's say you have 3 models, A, B and C.

A is related to B, and B is related to C. But you need to access all C's which is related to A (over B), then you need to use hasManyThrough() (think like countries -> users -> posts , and you need all posts from specific country)

hasManyThrough() is not totally meant for many to many relationships, it's more like a shortcut.

Check the documentation links, 1, 2 (Laravel 4.2), or 3, 4 (Laravel 5.x).

Upvotes: 37

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