Accessing CodeIgniter Models in Other Models

问题:

It used to be that within a CodeIgniter model you couldn't access another model.

$this->load->model('bar');
$this->bar->something();

Is this still valid, or have they changed it?

回答1:

Those are some VERY long answers for a simple question.

Short answer: This is now fully supported. Cross-load away if you feel like it!

回答2:

I strongly disagree with the notion that a "model" should only encapsulate a database table with simple CRUD operations. As noted in the Wikipedia article:

http://en.wikipedia.org/wiki/Model-view-controller#As_a_design_pattern

...that application layer is intended to do more than simply act as a single database table abstraction. Think about the meaning of the word "controller" -- it should act more as a director rather than being the entire application in and of itself. A "model" is a place for business logic. Most large scale applications in fact hold much of their business logic in the database itself (in the form of triggers, stored procedures, foreign keys, etc.).

I think the misunderstanding of what a "model" is is partly caused by the same (over-)hype of "MVC", without carrying with it much understanding of the concepts themselves. Kinda like how empty "AJAX" is, or even more easy, "Web 2.0". For better or worse, plenty of script kiddies have jumped on the MVC wagon, and since the simple howtos and example scenarios don't do much more than tell you to put your database code in the "model", the misuse of that layer as only a database abstraction has become commonplace. Now you read posts all over the Internet calling it "unpure", "dirty", "hackish" to put any business logic in a model. That's WRONG. Misinformed.

The easy example is to think about foreign keys: even if you only want your "model" to be a database model, if you want to be "pure", "correct" or what have you, you really should be enforcing referential integrity therein. Thanks to the lack of real foreign key support in MySQL for many years, web applications grew up without anyone worrying about referential integrity at all. Fits the script kiddie lifestyle I guess. Anyhow, for even this simplified view of a model to be able to maintain foreign key validity, a model then has to work with others (or, especially if a framework like CodeIgniter does not let you do so, you have to write queries to other tables, sometimes duplicating queries elsewhere - THAT is bad style).

Therefore, I believe this to be a shortcoming of CodeIgniter. I understand that it might not be an easy fix, but it's certainly a disappointing oversight.

So what I did was take the example code above and abstract it into a helper so that I now have a function that works almost identically to the normal $this->load->model() functionality. Here it is (put it into a helper that is auto-loaded and you can use it in any model):

   /**
    *
    * Allow models to use other models
    *
    * This is a substitute for the inability to load models
    * inside of other models in CodeIgniter.  Call it like
    * this:
    *
    * $salaries = model_load_model('salary');
    * ...
    * $salary = $salaries->get_salary($employee_id);
    *
    * @param string $model_name The name of the model that is to be loaded
    *
    * @return object The requested model object
    *
    */
   function model_load_model($model_name)
   {
      $CI =& get_instance();
      $CI->load->model($model_name);
      return $CI->$model_name;
   }

回答3:

It's possible, but not ideal and considered bad and more for "quick fix" than ideal or pure implementation.

class Location extends Model{
      public function get($ID){
                // Get main CI object handle and load model
                $CI =& get_instance();
                $CI->load->model('LocationType');
                // Call new model functions using handle to main CI object
                $CI->LocationType->setID($result->LocationTypeID);
                $CI->LocationType->setTitle($result->TypeTitle);
                $this->_locationType = $CI->LocationType;
                //Other Stuff
    }
}

Anytime you're using the main CI object like this is probably a bad idea. Try to re-think your layout and just pass data to/from your controller to the models.

http://codeigniter.com/forums/viewthread/69833/

回答4:

You can load models from models as Phil Sturgeon says, but you have to be careful of dependencies if you load the models in the model constructor: if model A uses model B and model B uses model A, when you try to load one or the other, you'll go into an infinite loop.

回答5:

In situations like this in Code Igniter I prefer one of two posiibilities:

1) Have model's attribute and setter like this:

class X extends Model {
  var $Y_model;
  public function setY($Y) {
    $this->Y_model = $Y;
  }

  public function doItRightNow($a,$b) {
    $list = $this->Y_model->getSomeList($a,$b);
    // ...
  }
  // ...
}

And then use this setter before other methods to give an instance of other model so it can be used by methods.

$this->load->model('X');
$this->load->model('Y');
$this->X->setY($this->Y);
$this->X->doItRightNow($something,$somethingElse);

2) To have a parameter in method by which I will give an other model instance from controller.

class X extends Model {
  public function doItRightNow($a,$b,$Y_model) {
    $list = $Y_model->getSomeList($a,$b);
    // ...
  }
  // ...
}

And use it like this:

  $this->load->model('X');
  $this->load->model('Y');
  $this->X->doItRightNow($something,$somethingElse,$this->Y);

I think that these are more clean possibilities.
Which way to use depends on how many methods need to access other model. If there are one or two it might be better to give it as a method parameter. If more - I think it's better to have a class attribute and setter.
And in elegant way you can give one model or another depending on some condition - if they both partially implement same interface with the same kind of data returned (it's rarely useful, but it can be sometimes).

回答6:

I think it's generally better the write libraries that access the models and then include the libraries in your model if need be.

For instance, if you needed to check if someone is authorized to go through with a certain CRUD action, you might want to include whatever authentication library you are using (its probably auto-included in most cases). You wouldn't necessarily want to access the model directly--it just seems dirty and improper.

I think the preferred way is to do what you need to do in your controller and pass the results from one model's method(s), if need be, to your other model's method(s).

Regardless, I can't see why it wouldn't be possible to include one model into another, per se. I don't think you can do it with the syntax you are showing, though. You would have to do it some other convoluted way. In any case, IMO, it's bad practice to include a model directly into another model.

回答7:

In CI 2.0 you can just call one model directly from another.

回答8:

Better to create a helper function instead of calling the function from another model so that it can be used in 2 models at a time and code can be reused.