I come from a Java/Grails background and cannot seem to find a definite answer online as to where the service logic for a CakePHP application should be stored. By "Services", I am talking about classes that are usually instantiated through dependency injection to conduct business logic on domain objects. They should be able to query any domain object and make changes in response to a controller action.
Currently, CakePHP's "Component" class seems to be the closest match to this behavior. I can load a component into any controller and execute its methods as needed. However, I have read in several places that components should never access the database and that doing so will result in some steep performance hits.
I have also looked into CakePHP's "Behavior" class and it doesn't seem to fit the ticket at all. It seems well-equipped to organize domain objects into a data structure setting, but that's not the kind of logic that a service would execute. Also, to import any model definition into a Behavior, I would have to edit the model definition itself to allow access, which is very awkward.
So I ask this question: Where should service logic be stored? Certainly not the controller, as it should only contain the minimal logic to process a request and send a response.
Components are the service layer in CakePHP. They are constructed by a dependency injection container (Components Collection) and get passed the controller, request and response that is to be handled.
There are no restrictions in what Components can do other than maintaining separation between layers. It is fine to use database connections, or use models, directly from a component and modify the request.
Components are actually very light-weighted if you only make them act for specific cases. Inspecting the action name, is a common way of limiting the reach of a component. You can also inject setting so it can know when is OK to execute custom service logic.
So I ask this question: Where should service logic be stored?
Certainly not the controller, as it should only contain the minimal
logic to process a request and send a response.
Sounds like the ideal use case for a Dispatcher Filter. It gets called even before a controller is instantiated. If you need to query the database simply load a model via ClassRegistry::init('YourModelName') and pass the request params to the model method and return whatever you need in your request. No controller needed at all. We've implemented oauth + xhttp using Dispatcher Filters without calling ever a controller.
How using a model inside a component should effect the performance... I don't know who got that strange idea, sounds like not the best article you found. It is true that you should not put model layer related logic in them but you can call a model for example through the controller instance and the controllers models.
Related
Below are two ways a service layer can be implemented in an CodeIgniter application.
1st method
1.send request to the controller
2.calling service layer methods from controller
3.return processed result data set(D1) from service layer to controller
4.then according to that data set controller demand data from model
5.model return data set(D2) to the controller
6.then controller send second data set(D2) to view.
2nd method
1.send request to the controller
2.calling service layer methods from controller
3.service layer demand data from model
4.model send requested data set(d1) to the service layer
5.after some processing return generated data(d2) to controller from service layer
6.then controller send data set(d2) to view.
What is the correct way of implementing a service layer in CodeIgniter? Other than these two methods, are there any other good ways?
if you can provide an example in Code it will be great
Please note, this is not necessarily the correct way of doing it, but I'm going to explain how a framework like might typically do it and then you can learn about other methods and decide the best one for your use-case. Therefore, I do not expect this answer to be the correct one, but I hope it imparts at least a little knowledge on how things are done before someone who actually knows what they're talking about comes along and chimes in (also to those people - please feel free to edit / downvote this answer :D). Finally this also has nothing to do with CodeIgniter but frameworks in general. Your question should not only be framed as framework-agnostic, but language-agnostic also.
So I'm going to offer an opinion here and that is of the fact that all modern frameworks, specifically in PHP, do not do MVC. Why is this important? Because we all need to be speaking the same language, and 'mvc' does not exist in PHP. That's a fact. Accept that and then we can move forward onto the bastardization of the concept that frameworks use; and CodeIgnitor is a particularly great example of 'MVC' bastardization; henceforth known as "mvc" with quotes.
The plus side is that frameworks like Symfony, for example, provide an initial opinionated architecture that at least contains some form of consistency across the application, and it goes something like this:
A standard HTTP request comes in and hits the front-controller, typically app.php or app_dev.php depending on whether or not you are in development or production; one involves a lot of caching that needs to be run on each change and the other doesn't - which is perfect for development.
A router matches the current url to a controller class and an 'action' (method) within that class.
The dependency injection part of the framework figures out what objects are needed for everything from the controller forward into the model layer and back, and either instantiates or prepares to instantiate them when needed.
The controller is instantiated with any required dependencies and the relevant method is executed. This is typically where you would start your development and 'hook your code in' to the framework.
This is where you decide on your architecture, however, the most important thing from both a developer perspective and business perspective (for lower costs for future maintenance) is consistency.
I personally prefer to ensure my code is decoupled from the framework. I pass in scalars taken from the request into an application-layer service, which uses objects from the model layer (passed-in via DI) to use domain objects. The point here is that domain objects are not directly passed into the controller, they are proxied through an application-layer medium, so you can theoretically replace the entire framework surrounding this and still, all you need to do is pass those scalars into this layer before they hit the model layer and it'll all still work (think CLI calls, no more controllers).
The application-level service uses any required Repositories, Services etc (and passes those scalars into them, remember the separation?), which perform business logic, (typically these are where your design patterns come into play on a day-to-day basis), and then return that data to the application-level service.
The service then returns the data to the controller and guess what? This is where frameworks tend to fuck up! Because there is no concept of a "View" in today's frameworks. There is only a template, and you pass that data to a template and bam that's it. So in your diagram, there is absolutely no concept of a view because that's not how things are done. And to be entirely honest, I'm still using templates because they're the fastest way of doing things, but until modern frameworks get their shit together and actually start using Views, we're out of luck and have to remain steadfast when confronting the fact that some (like Laravel) refer to themselves as "mvc" frameworks.
Note, Fabien Potencier explicitly states that Symfony was not an MVC framework - at least he knows what he's talking about there. Again, this is not purist, it's important we're all speaking the same, factually correct language in computing.
So, because you like diagrams so much, here's how some might do it with today's frameworks...
This is for an application that has the concept of a Review and Criteria for each Review. And don't even get me started on Symfony forms, they're so coupled to everything they're not a serious part of any architecture.
How many effing layers do you need? We already have "MVC", in DDD we have the concept of "Application", "Domain" and "Infrastructure" seperation, so get those two working together first, then this "service layer"? Do you really need another layer, or is the above enough? Things to think about...
See, you're not stuck with the framework / http request to get the application going as a result of this separation.
See the "services" in the above diagram? They're separated from the controller so you can throw scalars from anywhere and the application will still work. I think this will give you the separation you need. It's great to do things the right way, learn how to do it, and then learn how to control yourself and be pragmatic about it when it comes to the business and it's needs, but frameworks need to sort their stuff out - and you certainly wont be writing lovely code with CodeIgniter ;)
Dependency Injection and the Adapter pattern would be a good place to start.
CodeIgniter support's neither out of the box, so you would need to write a wrapper or maybe a hook.
Your view could only support xml|html as json would need to be pre-rendered to a .json file and then returned as output but this would need to be done via code, it's easier just to return the object in that case and altered on the frontend. PHP is an embedded language which works with (xml|html)
A service model works best when it is injected(dependency injection)
into a controller/model and is listed as a property of that controller/model.
The service is then bound to an interface
For example facebook/twitter
They both have a request and response function but both follow similar patterns, yet have different endpoints.
interface SocialMediaAdapter{
public request(url);
public response();
}
public class FaceBookProvider implements SocialMediaAdapter
{
public request(url){
}
public response(){
}
}
public class TwitterProvider implements SocialMediaAdapter
{
public request(url){
}
public response(){
}
}
public class SocialMediaServiceProvider{
protected $provider = null;
public function constructor(SocialMediaAdapter $provider){
$this->provider = $provider;
}
public function fetch($url){
return $this->provider->request($url);
}
}
Dependency Injection required here
new MyController( new SocialMediaServiceProvider ( new FacebookService ) )
IMHO there is no right or wrong here:
option #1 -
If you want to re-use the service layer in multiple controllers / actions
and feed it data from different models based on the request it makes sense to go for the first one.
option 2# - However the first option could be problematic if your data model is more complicated. What if a second call to the model is needed based on the data of a first call? Using the controller for this business logic defies the whole purpose of the service layer. In this case it might be better to go for the second one.
I think the second one is the more common one.
You should use first one. Because in MVC web application, controller is used to separate your business logic from view, it's something like a gateway. You need to start processing your info using controller, from controller you should call model or service layer or anything you need & finally you should return back data to any other source from here. Your view or service layer should not directly access model.
I have the common MVC situation in my PHP system: the Controller receive a request from the View containing $_POST data. Now I have three ways to handle the data:
a) The Controller only calls the Model and the Model handle the $_POST data.
b) The Controller transforms the $_POST data into variables and pass them to Model.
c) The Controller transforms $_POST data into a Model's domain object and only pass the object to Model.
Currently, I am following option A, but I believe it is wrong, so I am thinking of using option C.
So, according to MVC, what is the right way to handle $_POST data?
EDIT At the moment, I'm not using any MVC framework.
EDIT 2 Generally, the same Controller handles request from a browser, a web service, an offline application, etc, or each one has it own Controller?
The best option is to use #2 approach, with some alterations.
I would write it as something like this:
public function postLogin( $request )
{
$service = $this->serviceFactory->build('Recognition');
$service->authenticate( $request->getParam('username'),
$request->getParam('password') );
}
// Yes, that's the whole method
There is no need to actually create variables, if you have used something like a Request instance to abstract the user's input.
Also, you might want to replace theRequest::getParam()method with something likeRequest::getPost()- although I have come to the conclusion that, in a correctly structured application, theGETandPOSTparameters should not share same name.
The serviceFactory which you see in the code snippet would be an object that you inject in both controller and view instance. It would let you share same service instances between controllers and views.
It is responsible for creation of services (which would contain the application logic, while leaving the domain business logic in the domain objects), which helps you isolate the interaction between domain entities and storage abstractions from the presentation layer.
About the other options:
The Controller only calls the Model and the Model handle the $_POST data.
In the MVC and MVC-inspired design patterns the model should be aware of neither the user interface nor of the presentation layer as whole. The $_POST variable in PHP is a superglobal.
If you use it with model layer, your code becomes bound to the web interface and even the specific request method.
The Controller transforms $_POST data into a Model's object and only pass the object to Model
Not entirely sure what you meant with this. Seems you were talking about instantiation of an abstraction, which would contain the user's request. But in this case controller becomes responsible for instantiation/creation of said structure, which would violate SRP.
Closing notes:
One thing you must understand is that, in context of web based MVC applications, the User of your application is the browser. Not you. Browser sends the request, which is handled by routing mechanism and disseminated by controller. And view produces the response to your browser.
And the other thing is: Model is neither a class nor an object. Model is a layer.
Update
Generally, the same Controller handles request from a browser, a web service, an offline application, etc, or each one has it own Controller?
You should be able to have single controller, that deals with all the forms of application. But that is only on the condition, you are actually using same application for all 3 use-cases.
To do so there are two conditions:
you need to abstract the Request instance, that controller receives
the view should be instantiated outside the controller
This way you can have one application to fulfill all the requirements. Only thing, that each variant has different, is the bootstrap stage, where you create the Request instance and select the proper view.
In the situation, that you described, the changing part would actually be the view, since a REST or SOAP service would be expected to produce a different response than an ordinary web application.
Once upon a time was the three tiered application architecture.
It all depends on your MVC framework. Normally, the Controller does the link between the user and the model layer, which manipulate domain objects.
In the early days of MVC in PHP, the model layer was actually just the domain objects, called models for that purpose.
Some prefered having so called thin models, which only provide an OO representation of the data, (which simplifies persistence). In that case, the controller would regroup the so called actions, containing the bulk of the processing associated with an HTTP request (fat controller).
Others embedded most of said processing in the object model with dedicated methods (fat model).
However, at some point, you have to analyse the content of the query to sanitize and validate it, and this depends on how your view will format the request. Sanitization might be a controller task (this request should only contain these values), while validation is definitely a model task (values should be of these types).
An interesting question is: how do you deal with actions impacting several domain objects? Where do you put the logic for that?
Nowadays, the model layer is composed of services segregating the domain objects from the evil grasp of the controllers, to limit the dependencies between the layers to their respective interfaces only. This is where most of the request processing is done.
Symfony2, for instance, provides a sensible answer to this question: each step of the processing of a request is implemented in a dedicated piece of code, which could be described as the following:
the request is first turned into an object
that object is routed using a routing object
it is handled to a controller
the controller pass the request to the service concerned by the action, which build the response object
The service job is then broken in several steps:
validation (using a dedicated object which rely on rules described in a separate file),
construction/updating of domain objects (using serialization to/from db if necessary),
selection of a template for the response,
population of said template with the relevant data from the domains.
CakePHP is another popular framework which follows similar concepts: simple controllers, and services encapsulating domain objects.
See this question for a better insight on the general concepts.
See this other question for other answers.
Thanks to tereško for his invaluable input on the matter.
i am using Zend and following
the 2nd option .
Example a Registration form
step- 1 the forms sends me the post value to the specified controller
step -2 i will validate the form values for example ( mail and url and empty post values ) through server side validation .
step -3 send the checked post data either in variable or has whole to the model .
step 4- controller calls the model .
step -5 the models inserts the post values and creates a new user .
I think your second option is better regardless of framework or approah you use .
note - same controller can handle everthing depends on your application logic .
but i prefer to keep different controller for differnt user request and user types
it helps in keeping code readable managebale .
Look at some MVC frameworks.
For example, in Yii you can write such code inside action:
$model = new Model();
if(isset($_POST['Model'])) {
$model->attributes = $_POST['Model'];
}
Note, that all attributes of your model must be passed through validation rules. In Yii validation applies during (actually, before) $model->save()
See:
http://www.yiiframework.com/doc/guide/1.1/en/form.model#securing-attribute-assignments
http://www.yiiframework.com/doc/guide/1.1/en/basics.mvc
'C' is best option. You should not let raw $POST data go in model as model is supposed to be generic handling store and load operations mainly.
Example : same model can be used web interface and Web services. On Web $_POST is valid but for web services its not. So model doesnt care how data is received but only how to store and load it.
Yii is definitely a clean implementation of MVC.
So I've been studying the role of the repository pattern as a means of decoupling the persistence layer from my models in an MVC framework. Prior to this, I might have my UserModel calling active record methods directly in order to store/retrieve domain objects.
Here's a sketch of what I'm thinking in regards to the call stack in a request that should create a new User:
Here are my questions:
Is this a correct implementation of the repository pattern?
I understand that the controller should take the user's information from the request and pass it into the model. How does that usually happen? Should the controller create a User object and then pass that into the model? I sure as heck don't wanna just pass in an array of values into the model--nor do I want to pass in 15 arguments to the model method that creates a user.
In order for this pattern to really work, it looks like to me I would need to have a domain object that is just a simple data structure with no behavior and then if I'm using an ORM, I would have an ORM object which will describe how the object is persisted. Initially I resisted this because it feels like duplicate code, but if I'm really separating persistence from the business logic, this would be needed right? For example, what if I went with an in-memory store? I would no longer use the ORM object.
Am I thinking correctly here? Is this acceptable. Please help me connect the dots in my head.
1. Is this a correct implementation of the repository pattern?
I'm not sure where you been doing that research, but you have got it wrong.
Repositories as for separating the domain objects from data mappers.
There no such thing as "models". Model in MVC design pattern is one of the to main layers: presentation layer and model layer.
And the repository pattern is incompatible with active record (anti)pattern, which combines domain and storage logic in single instance, thus causing a major SRP violation.
To use a real world example for, when and how to use a repository here is an example:
You are creating some document management tool, where said documents can come from several sources (for example: local SQL database, SOAP service and cache). In this situation you create a repository, which deals with the "routing" of storage. It is the part of application, that decides which data mapper to use for storing/retrieving each document.
The goal of repository is to separate the domain logic from the interaction with storage. For the system, that was described above, a repository would also let add new data sources, without need to rewrite large amounts of code (if any). You could just add another type of mapper for the document.
2. Should the controller create a User object and then pass that into the model?
To begin with, controller itself should not create anything. Instead your controller should use a factory for acquiring instance of the object that you need. This factory can be provided to the controller through constructor or some other method. This is called: Dependency Injection (to learn more about it, watch this lecture).
Also, as noted above, model is a layer, not any specific class or object. The responsibility of controller is to alter the state of model layer (by passing data to it). You could interact with domain objects and mappers (or repositories) directly in the controller, but it would mean leaking some of the business logic in the controller. It is recommended to instead use services, which then manipulates said domain objects and storage related structures.
As for the issue with 10+ parameter, that you would require for creation of new user account, let's assume you have action with following footprint:
public function postUser( Request $request )
{
....
}
If the action gets called with specific Request instance, you have two options how to deal with large amount of parameters:
Wrap the instance in a decorator, which would let you call a single method for forming the data from request in a specific array. Then you pass this array to the service(s).
Form the array inside the controller's action and pass it, where th data is required.
The former solution is more suited for large scale applications, where such formation of data would be required repeatedly though-out the code. But in a small/medium projects the second option is the common-sense approach.
Thing is, the job of the controller is to take the user's input, and distribute it to the model layer and current view. And formation of such array fits right-in with this mandate.
3. (..) main object that is just a simple data structure with no behavior and then (..)
No. Domain object is not "simple data". It is where most of the domain business logic resides in the application.
And forget about magical ORMs. First step for implementing a repository is to separate the domain and storage logic. Domain object handles the validation and business rules, mapper deals with persistence and data integrity (small example here).
Another thing that you must realize is that repositories for web application do not really interact with in-memory persistence (apart from cache). Instead your repository would be juggling mappers for different data sources.
Should the controller create a User object and then pass that into the model?
I'm not sure what you mean by "pass that into the model" -- the User object is the model. "Controller" and "model" represent different layers in the design, they are not specific objects, and there shouldn't be a separate UserModel object as you mentioned.
The repository interface itself is generally considered part of the model, though the domain objects shouldn't be saving themselves -- this should be done in the controller.
Your controller's job would then be to interpret the request and create a User object, then use the repository to save the user:
$user = new User(...); // based on Request
$repository->save($user);
it looks like to me I would need to have a domain object that is just a simple data structure with no behavior
This is not true, you can and should encapsulate behaviour in your domain objects. As for how persistence is actually implemented, a good ORM should take care of most of the details and you shouldn't have to create additional classes by hand.
I've been using the CodeIgniter framework for PHP and am enjoying it, but I notice that it seems to require a controller for every view. I'm wondering if there is a way to call a specific model from the view itself, rather than route through a controller. I understand that use of a controller is best practice in most cases, especially where the data from the model needs to be modified in some way, but I have cases where I just need to do a strict data pull to the view (which is loaded via ajax), and setting up a controller for that seems superfluous.
Any thoughts? Thanks in advance!
You're fundamentally misunderstanding MVC, at least as implemented in CI.
All URLs on your site (at least those that utilize the CI framework) are mapped to functions (methods) within controllers.
http://myCIsite.com/controller/method[/var1][/var2]...
It doesn't matter whether the URL is accessed via regular HTTP or via AJAX. This is always a one to one mapping. Because of this, you should think of the controller/method combination as the "web page". Do not think of the view as the web page.
Models and views are subordinate to controllers. The controller delegates specific responsibilities to them - database interaction for models, and page output to views.
Because models and views only serve to perform delegated responsibilities, their use is not required in any given controller/method. Help pages, for example, generally have no need to interact with a database, so there is no model utilized by the controller/method combination that serves a given help page. Likewise, form handlers frequently redirect to another page upon completion of processing. As such, there is no view corresponding to the form handler (but there is (likely) a view called from the controller/method in the redirected to page).
Furthermore, models and views do not necessarily correspond on a one to one basis with individual controllers/methods. Any given model can be loaded and used from within several controllers. Similarly, a controller could have a single monolithic view that is used by all methods, or each method could be assigned its own view. (Or, as I just said, a given controller/method could utilize no view at all.)
Finally, CI does not enforce strict MVC separation. You can interact with the database and echo HTML all from within the controller and CI will not complain. Nevertheless, this separation and delegation of responsibility is followed because logically separating the responsibilities makes the code easier to read and helps you follow the DRY principle in your coding.
The fundamental Understanding is that the "web page" corresponds to the controller/method. The view and model, when used, handle delegated responsibilities for the controller/method.
I'm wondering if there is a way to
call a specific model from the view
itself, rather than route through a
controller.
That's not possible as of what I know, the main abstract class of the CI controller imposes restriction to use a controller otherwise you will get a fatal error.
And actually what you say will break the best practice of MVC design pattern. You got to go to model through a controller not view.
I'm a bit confused as to exactly what you're trying to achieve. The controller's value, aside from just being a clean way to handle incoming requests, is to manage the interaction between the models and the views and to determine which views to load. It's also entirely reasonable to load model data directly from your views, but how did you get to your view in the first place?
I guess I'm just having a hard time seeing the context here..
To run a query via Ajax you still need to provide a URL / path in the javascript call. You can not get around the fact that a controller function has to "catch" this call; you can not map a url directly to a model. All you need is 3-4 lines of code in your controller.
Via URI routing you can map a URL to a different controller, so you don't "require a controller for every view". I always create a controller called "ajax" to handle those requests.
A basic ajax call with jquery can be something like this
$('#prod_img').load( "http://domain.com/ajax/get_img", {'color': 'blue', 'url_title': 'bla' } )
You can echo stuff in your controller, so rather than trying to bypass the controller you should be looking into how to do away with the views. This will actually be easy, you can load the db class in the controller just as you can in a model.
But if you really don't want to use MVC perhaps Codeigniter is not the framework for you.
You should read more into the principles of MVC.
Views are strictly for presentation of data, the model shouldn't communicate with views directly.
But still if that's what you want then just pass $this->db from the controller to the view and use it in the view.
Then again, this is NOT a good practice.
I recently read this post which led to a series of other posts that all seem to suggest the same idea: Models do everything, the View should be able to communicate directly with the model and vice versa all while the Controller stays out of the way. However, all of the examples shown are fairly simplistic and none really show an example of how anyone has tried to implement full handling of of a request / response cycle, which got me to wondering "should the model be responsible for handling the request (ie $_GET, $_POST, etc) itself?" and "should the controller only operate as a pass-through to instantiate the necessary model(s) and pass the model(s) to the view?". (In fact I found one example taken the extreme of embedding a Zend_Form object in the model)
From my reading of what Fowler says about MVC and just controller's in general it seems at first glance that the thinner the controller layer the better. But then I took the time to back through and study what he says about both MVC and Front Controller (which just muddies the waters because both patterns define controllers) and now my instincts suggest that Zend_Framework in implementing both of these patterns, has actually created a composite object that performs the functions of a Controller in MVC and those of a Command object in Front Controller (or some such).
So I'm wondering what the general opinions would be of others who have implemented similar patterns in their apps - do you handle the request entirely within the controller layer or do you make the model aware of the request and handle parameters directly within the model?
My first thought is to avoid handling any sort of request in the model. That is the job of the controller. Here is why: suppose you have a model that does handle your requests (GET or POST). That structure will likely work well initially. Now, suppose you want to add some sort of AJAX functionality or put up a service interface to your system. Now that you accept more than simple GET/POST, i.e. JSON or XML, your model will have to distinguish between each request type and know how to parse them. I believe that destroys a lot of simplicity and clarity of the model code. I agree that the controller layer should be thin, but it should also have a role and an expertise. For me a controllers expertise is to:
Handle incoming requests
Delivery data to the model
Request/accept data from the model
Pass the data's model to the view
I vacillate on how much the view should know about the model. Some people recommend the model go straight into the view, but I think that is fragile coupling. It frequently leads to logic in the view. Also, if you are working on a project where the team members working on the view are not as programming savvy as the main developers it puts a large burden on them to keep up with changes. I tend to package the data I hand to my views in a neutral structure instead of handing over the full models.
My interpretation of MVC is mostly pragmatic. The model's job is to model the domain you are working on and should not care where the data comes from. I frequently structure model code with the assumption that it could be used outside of the web application in perhaps a command line application or a desktop application. That sort of union rarely happens, but it leads to clear purpose of each layer. The controllers job is to move data between involved parties, be they client requests, the models, or the view. The controller should have very little domain logic, but that doesn't mean it doesn't have any code. Finally, the view should just look pretty. Hope that helps.
handling the user instructions/input (like HTTP requests) is the job of the controller. model is for working/manipulating/fetching the data and view is for showing the results to user. this means that connection between the view and the model is duty of a controller most of times.