Laravel: return JSON model with relation - php

Question

I'm trying to query a model with a relation.
My method:
public function getLabel($layerId)
{
$labelGroups = Forum_label_group::
join('forum_layer_to_labels', function ($join) use ($layerId) {
$join->on('forum_layer_to_labels.layerId', '=', 'forum_label_groups.id');
})->with('labels')->get()->toJson();
return $labelGroups;
}
The output:
[{"id":4,"name":"Demogruppe","description":"bla","required":1,"created_at":"2016-10-22 12:29:27","updated_at":"2016-10-22 12:29:27","labelGroupId":2,"layerId":2,"labels":[]},{"id":5,"name":"Demogruppe 2","description":"bla 2","required":0,"created_at":"2016-10-22 12:29:27","updated_at":"2016-10-22 12:29:27","labelGroupId":2,"layerId":3,"labels":[]}]
As you can see, the label relation is empty.
Now I'm trying to query a single model instead off all:
public function getLabel($layerId)
{
return Forum_label_group::with('labels')->first()->toJson();
}
the new output:
"{"id":2,"name":"Demogruppe","description":"bla","required":1,"created_at":"2016-10-22 12:29:27","updated_at":"2016-10-22 12:29:27","labels":[{"id":5,"title":"Demo rot","name":"demo-rot","typeId":3,"groupId":2,"created_at":"2016-10-22 12:29:47","updated_at":"2016-10-22 12:29:47"},{"id":6,"title":"Demoblau","name":"demoblau","typeId":1,"groupId":2,"created_at":"2016-10-22 12:30:03","updated_at":"2016-10-22 12:30:03"}]}"
And as you can see now, everything is fine. The whole relation exists. Is there a problem with the initial query? The relation seems to be ok.

Answer 1

And of course it was an small issue ;)
I forgot to add a select() on my query. The original id has been overwritten by the join(). So the method tried to query an labelGroup that doesn't exist.
The correct query:
public function getLabel($layerId)
{
$labelGroups = Forum_label_group::
join('forum_layer_to_labels', function ($join) use ($layerId) {
$join->on('forum_layer_to_labels.layerId', '=', 'forum_label_groups.id');
})->select('forum_label_groups.*')->with('labels')
->get();
return $labelGroups;
}