Laravel Many to many - Unexpected result set on ->select() - php

Question

I wonder if anyone can help, as I've hit a wall and still learning Laravel ORM. Can anyone explain why, when I run:
public function locationTags(){
return $this->hasMany('App\UserHasLocationTags', 'user_id')
->join('location_tags AS lt', 'lt.id', '=', 'location_tag_id');
}
I get this result set: (snipped...)
{
"id": 1,
"created_at": "2015-05-13 13:04:56",
"updated_at": "2015-05-13 13:04:56",
"email": "REMOVED",
"firstname": "REMOVED",
"lastname": "REMOVED",
"location_id": 0,
"deleted_at": null,
"permissions": [],
"location_tags": [
{
"user_id": 1,
"location_tag_id": 1,
"id": 1,
"created_at": "2015-05-13 13:06:28",
"updated_at": "2015-05-13 13:06:28",
"name": "Test Tag 0",
"location_id": 1,
"deleted_at": null
},
{
"user_id": 1,
"location_tag_id": 2,
"id": 2,
"created_at": "2015-05-13 11:40:21",
"updated_at": "2015-05-13 12:56:13",
"name": "Test Tag 123",
"location_id": 1,
"deleted_at": null
}
]
}
Which is ace! However, when I start to select the columns I want from the location_tags join, with:
public function locationTags(){
return $this->hasMany('App\UserHasLocationTags', 'user_id')
->join('location_tags AS lt', 'lt.id', '=', 'location_tag_id')
->select('lt.id', 'lt.name');
}
I end up with:
{
"id": 1,
"created_at": "2015-05-13 13:04:56",
"updated_at": "2015-05-13 13:04:56",
"email": "REMOVED",
"firstname": "REMOVED",
"lastname": "REMOVED",
"location_id": 0,
"deleted_at": null,
"permissions": [],
"location_tags": []
}
Can someone explain what's going on? And possibly point me in the right direction to limit the selects? Thanks!
Update
I've also tried:
$query = \App\User::with(['permissions', 'locationTags' => function($query){
$query->select('lt.id', 'lt.name');
}]);
Which returns the same result :(

Answer 1

Figured it out. The key here was that you must include a select() value of at least one key that Laravel can use to map the result set. In my case it was user_id, like so:
public function locationTags(){
return $this->hasMany('App\UserHasLocationTags', 'user_id')
->join('location_tags AS lt', 'lt.id', '=', 'location_tag_id')
->select('user_id', 'lt.name', 'location_tag_id');
}
Which then returns a much nicer results set:
{
"id": 1,
"created_at": "2015-05-13 13:04:56",
"updated_at": "2015-05-13 13:04:56",
"email": "REMOVED",
"firstname": "REMOVED",
"lastname": "REMOVED",
"location_id": 0,
"deleted_at": null,
"permissions": [],
"location_tags": [
{
"user_id": 1,
"name": "Test Tag 0",
"location_tag_id": 1
},
{
"user_id": 1,
"name": "Test Tag 123",
"location_tag_id": 2
}
]
}
Hope this helps someone out in the future, because it kept me guessing for a good couple of hours.

Answer 2

I'm sorry but you've gone a little sideways here. The relationship definition should just define the Relationship. It's a powerful feature that supports many other aspects of the ORM. What you've done here is more or less build a custom Query, severely limiting the effectiveness of the relationship.
Up until recently, the proper way would have looked something like this.
// class User
public function userHasLocationTags() {
$this->hasMany('App\UserHasLocationTags', 'user_id');
}
// class UserHasLocationTags
public function locationTags() {
$this->hasMany('App\LocationTags', 'location_tag_id');
}
And you would eager load all the results like this.
$user = User::where('id', 1)->with('userHasLocationTags.locationTags')->first();
The code above produces in 3 queries. One to get the User, one to get all the UserHasLocationTags and a one to get all the LocationTags. This may seem wasteful on first blush but consider the following.
$users = User::take(100)->with('userHasLocationTags.locationTags')->get();
Again, this is only 3 queries but now you have loaded 100 users with all their location tags.
But I can see you are a man with an eye for efficiency, and loading all the intermediate relationships and the whole nested hierarchy probably doesn't sit well with you. Well good news! Laravel 5 has added another relationship type for just this situation. hasManyThrough (scroll down a bit to find it).
Has Many Through
The "has many through" relation provides a convenient short-cut for accessing distant relations via an intermediate relation. For example, a Country model might have many Post through a User model.
So in your case it may look something like this...
// class User
public function locationTags()
{
return $this->hasManyThrough('App\LocationTags', 'App\UserHasLocationTags');
}
$users = User::take(100)->with('locationTags')->get();
So now we are down to two queries. If you feel the need to optimize this further and only select specific columns, you can modify the eager load.
$users = User::take(100)->with(['locationTags' => function ($query)
{
$query->select('user_id', 'name', 'location_tag_id');
})->get();
And if you do that frequently, you should wrap it up in a scope.