Multiple nested queries in Laravel Eloquent - laravel

Question

I have a chat app, and I need to filter those user conversations that have attachment[s] in the groups last message, by using eloquent ORM. I have following DB tables/models:
Groups & Users. Relation is N-N between them, so there's a pivot table between groups and users, named group_user. Although this table has been expanded with some extra fields, as a result group_user have it's own model now.
Messages. Relations are 1-N from both groups and users.
Attachments. Relation is 1-N from messages.
The algorithm of this filtering isn't the problem - take user (because I need specific users groups) and his groups, find all group messages, sort them by date of creation in descending order and take the top one. And then check whether this message have any records in 'attachments' table. Obivously I do have all the relations defined in the respective Models. Right now I have this code, but it returns all groups that have attachments in any of the messages.
Also, I need to sort the query by the last message 'created_at' date.
return $user->user_groups()->whereHas('group', function($query) {
$query->whereHas('messages', function ($query) {
$query->whereHas('attachments');
});
})->with('group')->latest()->paginate($this->group->getPerPage());
Edit.
class User
{
public function messages()
{
return $this->hasMany('App\Models\Message');
}
public function user_groups()
{
return $this->hasMany('App\Models\GroupUser');
}
}
class Message
{
public function attachments()
{
return $this->hasMany('App\Models\Attachment');
}
public function author()
{
return $this->belongsTo('App\Models\User');
}
public function group()
{
return $this->belongsTo('App\Models\Group');
}
}
class Attachment
{
public function message()
{
return $this->belongsTo('App\Models\Message');
}
}
class GroupUser
{
public function user()
{
return $this->belongsTo('App\Models\User');
}
public function group()
{
return $this->belongsTo('App\Models\Group');
}
}
class Group()
{
public function messages()
{
return $this->hasMany('App\Models\Message');
}
public function group_users()
{
return $this->hasMany('App\Models\GroupUser');
}
}

Answer 1

Add a groups relationship to your User model:
public function groups() {
return $this->belongsToMany('App\Models\Group');
}
Then try this:
$user->groups()
->select('groups.*')
->join('messages', function($join) {
$join->on('groups.id', 'messages.group_id')
->where('created_at', function($query) {
$query->selectRaw('max(created_at)')
->from('messages')
->where('group_id', DB::raw('groups.id'));
});
})
->whereExists(function($query) {
$query->from('attachments')
->where('attachments.message_id', DB::raw('messages.id'));
})
->orderByDesc('messages.created_at')
->paginate($this->group->getPerPage());