Why belongsTo() return null?

Question

I have two models and two tables. First model name Inbox with database structure:

And second model name is StudentData with database structure:

And I will return with route('/sended') all mesages using my method for get needed messages:

public function getMessages($message_type = "new")
{
    $user_id = Auth::user()->id;

    $inbox = new Inbox();

    $paginate = 3;

    switch ($message_type) {

        case 'sended':
            $messages = $inbox->where('sender', $user_id)
                              ->where('trashed_in_sender', 0)
                              ->where('show_in_sender', 0)
                              ->orderBy('created_at', 'desc')
                              ->paginate($paginate);
            break;
        default:
            return abort(404);
            break;
    }

    return $messages;
}

And I have methods in my model Inbox :

public function messageSender()
{
    return $this->belongsTo("App\StudentData", 'sender');
}

public function messageRecipient()
{
    return $this->belongsTo("App\StudentData", 'recipient');
}

When I call in view $message->messageSender in result given NULL. Why I can't get data using sender id from inboxes table in student_datas table

Answer 1

So, I have a few questions....

1) How exactly does your User and StudentData models interact? It kinda seems strange to have 2 models with what seems to be a 1:1 relationship? Why not just use a User model?
(Do you even have a User model or am I misinterpreting things?)

2) I think your direction is wrong... if you already have a User model, try to get the sent messages from there. I will give you an example.

Let's say you have a User model and a Inbox model, where you have a "sender" and "recipient", which both have an id of the User model.
So in the Inbox model we have:

public function messageSender()
{
    return $this->belongsTo("App\User", 'sender');
}

public function messageRecipient()
{
    return $this->belongsTo("App\User", 'recipient');
}

But why not go from the other direction? We can write the relationships in the User model like

public function sentMessages()
{
    return $this->hasMany("App\Inbox", 'sender');
}
public function receivedMessages()
{
    return $this->hasMany("App\Inbox", 'recipient');
}

Now you can get all sent messages (ie all messages where the user is the sender) just by using

$user->sentMessages

and operate on that. Or you could even set up a special helper relation (my name sucks, find a better one... just for example)

public function unreadSentMessages()
{
    return $this->hasMany("App\Inbox", 'sender')
                ->where('trashed_in_sender', 0)
                ->where('show_in_sender', 0)
                ->orderBy('created_at', 'desc');
}

and can either use $user->sentMessages for all his messages or $user->unreadSentMessages for only the ones you need in your case.