非静态方法不应静态调用

Question

I am using a repository pattern and am trying to establish relationships between models. When I try to run the store() method (in the controller) which is trying to use the user() method (which establishes the relationship with the Party model), I get the following error message:

Non-static method Party::user() should not be called statically, assuming $this from incompatible context

I don't understand why I get this error when I try to run the user() relationship method, but all of the other methods (including $this->party->all(), $this->party->create($data)), work just fine.

Here is the relevant code:

// PartiesController.php
public function __construct(Party $party){
  $this->party = $party
}

public function store(){
  $data = Input::all();
  $user = Sentry::getUser(); 
  $this->party->user()->create($data);
}

// Party.php
class Party extends Eloquent{
  public function user(){
    return $this->belongsTo('User');
  }
}

// User.php
use Cartalyst\Sentry\Users\Eloquent\User as SentryUserModel;

class User extends SentryUserModel implements UserInterface, RemindableInterface {
  public function party(){
    return $this->hasMany('Party');
  }
}

// PartyRepository.php
namespace repositories\Party;

interface PartyRepository{
  public function all();

  public function findByID($id);

  public function create($input);

  public function user();
}

// EloquentPartyRepository.php
namespace repositories\Party;
use Party;

class EloquentPartyRepository implements PartyRepository{
  public function all(){
    return Party::all();
  }

  public function create($input){
    return Party::create($input);
  }

  public function user(){
    return Party::user();
  }
}

Answer 1

The issue is because you are calling a non-static method in a static context. You may be used to seeing the way Laravel does a lot of this (eg User::find() and the like). These, in reality though, are not static calls (a class instance is actually being resolved behind the scenes and the find() method invoked on that instance).

In your case, it is just a plain static method call. PHP would allow this, except for the fact that in the method you are referencing $this and PHP doesn't know what to do with it. Static method calls, by definition, have no knowledge of any instances of a class.

My advice would be to inject an instance of your Model class into your repository's constructor, something like this:

//Class: EloquentPartyRepository
public function __construct(Party $party) 
{
    $this->party = $party;
}

public function user($partyId) 
{
    return $this->party->find($partyId)->user();
}

The Party instance you send to the constructor should not be a record from the database, just an empty instance of Party (ie new Party() ), though I believe if you just add it to the constructor, the IoC should be able to leverage dependency injection and provide you with an instance.

An equivalent implementation is here, that adds a byId method:

//Class: EloquentPartyRepository
public function __construct(Party $party) 
{
    $this->party = $party;
}

public function byId($partyId)
{
    return $this->party->find($partyId);
}

public function user($partyId) 
{
    if($party = $this->byId($partyId)) {
        return $party->user();
    }

    return null;
}

Answer 2

I have solved the problem. Thank you @watcher and @deczo for your feedback. Both were very helpful and relevant to this error message.

In the end, I only needed to change one line. I had the sequence of method calls out of order in the store() function. Here is the relevant code.

// PartiesController.php
public function store(){
  $data = Input::all();
  $user = Sentry::getUser(); 
  $user->party()->create($data);
}

In my case, to remove the non-static error and to properly insert the User model into the Party model, I only had to make the aforementioned change.

I referred to http://laravel.com/docs/eloquent/#inserting-related-models for the appropriate sequence.