[Proposal] Belongs to through

[Nirlah]

The inverse of the hasManyThrough() relationship.

class Post extends Eloquent {

    public function country()
    {
        return $this->belongsToThrough('Country', 'User');
    }

}

Anyone else find it useful but me?

[anlutro]

Can't you use the same relationship both ways? HasManyThrough is effectively a m:m relationship, after all.

[taylorotwell]

You would just use the same relationship both ways.

[BenjaminRH]

Unless I'm missing something entirely obvious, which is quite possible, I don't think it is possible to use the hasManyThrough relationship both ways. This example illustrates:

Schema

Table 1: id, table_2_id, foo
Table 2: id, table_3_id, bar
Table 3: id, baz

Problem

Table 3 can have a hasManyThrough relationship with Table 1. However Table 1 cannot have a hasManyThrough relationship with Table 3 because Table 2 does not have a table_1_id.

[MaazAli]

I'd like to see a belongsToThrough relationship for models that work like the following

entry -> daily -> weekly

entry

• daily_id

daily

• weekly_id

so if I want to find the week that entry belongs to, I can do a belongsToThrough using daily as the intermediate table.

[upngo]

Would also like this relationship. The relationship as it currently stands can't necessarily be used both ways.

My schema
table_a: id
table_b: id table_a_id
table_c: id table_b_id

I can use a hasManyThrough on table_a to get to table_c
but I can't use it to get from table_c to get to table_a

Strictly speaking, in my case from table_c to get to table_a I want a belongsToThrough relationship..

[ifaniqbal]

How about this schema:

table user:
    id_user

table group:
    id_group

table permission:
    id_permission

table user_group:
    id_user_group
    user_id
    group_id

table group_permission:
    id_group_permission
    group_id
    permission_id

How is the best way to retrieve permissions for one user?
Thanks.

[szainmehdi]

I also can't see how hasManyThrough can work both ways. Here is my current issue:

stores:
    id

categories:
    id
    store_id

items:
    id
    category_id

In this case,

Store -- > hasMany -- > Category
Category --> hasMany --> Item

Item --> belongsTo --> Category
Category --> belongsTo --> Store

Store :: Category :: Item

Item :: Category :: Store

With Laravel 4.1, we can now use hasManyThrough to skip Category and go straight from Store to Item.

Store :: Item [√]

What we can't do is the inverse:

Item :: Store [X]

likely because categories doesn't have a item_id, which it obviously shouldn't have.

Am I missing something? Or is this intended behavior?

###Edit:
Also, even if it does somehow work, it's not ideal since the definition will return a Collection instead of a single instance, like belongsToThrough would ideally return.

[szainmehdi]

See this StackOverflow answer providing a workaround:
http://stackoverflow.com/questions/23365905/laravel-hasmanythrough-equivalent-belongsto-relationship-through-another-model

The only issue with this is that eager-loading using this method doesn't work:

$item = Item::with('store')->first();
dd($item->store); // => null

[vladrusu]

+1 for BelongsToThrough

[Nirlah]

@taylorotwell Maybe you should reconsider it again...

[vladrusu]

@taylorotwell As @szainmehdi said earlier, belongsToThrough wouldn't be quite the same as HasManyThrough, because HasManyThrough is a m:m relationship and returns a collection, but what we need in belongsToThrough is to return a single object, not many.

Consider the following example. Supposing we have a users table... For each user we store the city (via a city_id field), but NOT a country. The country is stored in the cities table. We could of course define a "country_id" (in addition to city_id) as well in Users table, but that would break the DRY principle.

It's clear that each City has one and only one country. So a HasManyThrough relationship would be useless.

class User extends Eloquent {

protected $table = 'users';

public function city()
{
    return $this->belongsTo('Cities', 'city_id');
}

public function country()
{
    return $this->belongsToThrough('Country', 'Cities');
}

}

[szainmehdi]

Yep, I definitely hope you'll reconsider this proposal, @taylorotwell. It has concrete use-case scenarios and I've found myself needing this relationship twice now in my own projects.

[markmooibroek]

Would be awesome if you could implement this. I just started with Laravel but already in need of this =)

Currently using this to emulate the belongsToThrough (in User model to lookup connected church)

User m--1 Address m--1 Church

public function church(array $columns = null)
{
    return $this->address()->first(["id", "church_id"])->church()->first($columns);
}

[adonespitogo]

+1 for belongsToThrough

[d-lit]

+1 for belongsToThrough

[GrahamCampbell]

Discussion can continue on #6161.