If one needs JSON, XML, etc. als output format, one can use the AcceptableViewModelSelector Controller Plugin or / and (?) alternate rendering / response strategies.
When should the one and when the other (and when a combination) be applied?
Can/should they be combined?
Well, the Strategies are basically listeners. Listeners that give action depending on what kind of Model will be returned from your Controllers actions. If you return a ViewModel the PhpRendererStrategy will take place. If you return a JsonModel, the JsonStrategy will do it's stuff and if you return a FeedModel it's the FeedStrategy doing it's thing.
However the Strategies only apply if they are registered. So if you return a JsonModel without having the JsonStrategy registered, then nothing will happen.
The AcceptableViewModelSelector exists to provide an easier access and handling of different ModelFormats depending on the accept header. It helps to make things easier, no more, no less.
Strategies, you can also register your own one. There's modules out there that have a PdfStrategy which will render out a PDF-Document if you tell it to.
To tune this down a little to your question:
Strategies have been there from the start of ZF 2.0
The controller plugin AVMS only got in sometime within ZF 2.1 to just make things easier - that's why it's nothing more than a "plugin" ;)
If that doesn't really cover your question, i'm quite insecure on how to answer you ^^
Related
As a newcomer to spring I would like to know the actual difference between:-
#PostMapping
#PutMapping
#PatchMapping
My understanding is PUT is for update but then we have to get the element by its id and then save() it. Similarly the save() method is again used by Post which automatically replaces by its identifier(PRIMARY). In my application I am able to use three of these methods interchangeably.
What is the point of having PATCH, POST, PUT types when we use repository save methods for all?
HTTP method tokens are used to define request semantics in such a way that general purpose components (browsers, reverse proxies, etc) can exploit the information to do intelligent things.
The easiest of these is that PUT has idempotent semantics; if an http response is lost, a general purpose component knows that it may autonomously retry sending the request. This in turn gives you a bit of extra reliability over an unreliable network, "for free".
The fact that your origin server uses the same persistence mechanism for each is an implementation detail, something deliberately hidden behind the "uniform interface".
The difference between PATCH and POST is subtle; PATCH gives you an unambiguous way to designate that the enclosed entity is a patch document, and offers a mechanism for discovering which patch document formats are understood by the origin server, neither of which you get from POST alone.
What's less clear, at least to me, is whether PATCH semantics allow an intermediate component to do something intelligent with a request - in other words, do the additional constraints (relative to POST) allow intermediaries to do anything interesting?
As best I can tell, the semantics of a PATCH request are more specific, but not actionably more specific -- certainly not as obviously as we have in the case of safe or idempotent request semantics.
POST is for creating a brand new object.
PUT will replace all of an objects properties in one go.
Leaving a property empty will empty the value in the datastore.
PATCH does a partial update of an object.
You can send it just the properties which should be updated.
A PATCH request with all object properties included will have the same effect as a POST request. But they are not the same.
The HTTP method is a convention not specific to Spring but is a main pillar of the REST API specification.
They make sure the intent of a request is clear and both the provider and consumer are in agreement of the end result.
Kind of like the pedals or gear shift in our cars. It's a lot easier when they all work the same.
Switching them up could lead to a lot of accidents.
For us as developers, it means we can expect most REST APIs to behave in a similar way, assuming an API is implemented according to or reasonably close to the specification.
POST/PUT/PATCH may look alike but there are subtle differences.
As you mention the PUT and PATCH methods require some kind of ID of the object to be updated.
In an example of a combined POST/PUT/PATCH endpoint, sending a request with an object, omitting some of its properties. How does the API react?
Update only the received properties.
Update the entire object, emptying the omitted properties.
Attempt to create a new object.
How is the consumer of the endpoint to know which of the three actions the server took?
This is where the HTTP method and specification/convention help determine the appropriate course of action.
Spring may facilitate the save method which can handle both creation, updates and partial updates. But this is not necessarily the case for other frameworks in Java or other languages.
Also, your application may be simple enough to handle POST/PUT/PATCH in the same controller method right now.
But over time as your application grows more complex, the separation of concerns makes your code a lot cleaner, more readable and maintainable.
I have doubts whether every view should have its own ViewModel or should I pass the plain model where there is no need for ViewModel? (What concerns me is that if I start to mix these two concepts, then I will end up with jungle later on)
I tried to google it but no one talks about that, every post I run into just explains the purpose of ViewModel and I know that the main purpose of ViewModel is so you can pass multiple models to view.
It depends.
In many use cases the main purpose is not to expose fields to being bound on form submission that the user shouldn't be able to update. I wouldn't slavishly create them when not needed but it depends on the developers and their level of understanding on when and why you use viewmodels vs domain/ef models. Also application code base size makes a difference.
Maybe you need select lists, maybe you want to convert some properties to different types. Lots of reasons to use them. However it is more code and mapping code even if you use a tool like AutoMapper. So they cost time to implement but maybe they fix problems and save other time? Maybe they fix a security problem? Maybe doing them all the as view models helps juniors understand? Maybe you would rather do the setup of a viewmodel at start than convert code later when it is really needed?
Consistency can help but doing a bunch of extra work may not be worthwhile. Best practice for me isn't best practice for you.
Consider the costs and benefits for your project and team . E.g. maybe your project is internal and no one is going to try to hack via adding data to submission
There are couple of reason to choose ViewModel over DomainModel.
1) First thing first is the security. Imagin you have a view for changing the password. If you pass the domain model to the view. probably you are exposing a lot of properties which is not necessary and it may cause a security problem. There is no reason to expose properties like LastLoginDate, IsActive, IsEnabled, NumberOfFailedLogin and so on for just changing the password.
2) The second reason is reducing logic from the view. If you pass a Domain class to the view, Possibly you need to add some extra logic for hiding extra properties or shape it as you like or adding logic based on the route and etc.
3) Because of the architecture. Exposing domain model to the view cause tightly coupling between your presentation layer and domain model which is not good at all.
Until now, in my MVC application, I've been using the Model mainly just to access the database, and very little else. I've always looked on the Controller as the true brains of the operation. But I'm not sure if I've been correctly utilizing the MVC model.
For example, assume a database of financial transactions (order number, order items, amount, customer info, etc.). Now, assume there is a function to process a .csv file, and return it as an array, to be inserted into the database of transactions.
I've placed my .csv parse function in my Controller, then the controller passes the parsed information to a function in the Model to be inserted. However, strictly speaking, should the .csv parsing function be included in the Model instead?
EDIT: For clarity's sake, I specifically am using CodeIgniter, however the question does pertain to MVC structure in general.
The internet is full of discussion about what is true MVC. This answer is from the perspective of the CodeIgniter (CI) implementation of MVC. Read the official line here.
As it says on the linked page "CodeIgniter has a fairly loose approach to MVC...". Which, IMO, means there aren't any truly wrong ways to do things. That said, the MVC pattern is a pretty good way to achieve Separation of Concerns (SoC) (defined here). CI will allow you to follow the MVC pattern while, as the linked documentation page says, "...enabling you to work in a way that makes the most sense to you."
Models need not be restricted to database functions. (Though if that makes sense to you, then by all means, do it.) Many CI developers put all kinds of "business logic" in Models. Often this logic could just as easily reside in a custom library. I've often had cases where that "business logic" is so trivial it makes perfect sense to have it in a Controller. So, strictly speaking - there really isn't any strictly speaking.
In your case, and as one of the comments suggests, it might make sense to put the CSV functionality into a library (a.k.a. service). That makes it easy to use in multiple places - either Controller or Model.
Ultimately you want to keep any given block of code relevant to, and only to, the task at hand. Hopefully this can be done in a way that keeps the code DRY (Don't Repeat Yourself). It's up to you to determine how to achieve the desired end result.
You get to decide what the terms Model, View, and Controller mean.
As a general rule MVC is popular because it supports separation of concerns, which is a core tenet of SOLID programming. Speaking generically (different flavors support/ recommend different implementations), your model holds your data (and often metadata for how to validate or parse), your view renders your data, and your controller manages the flow of your data (this is also usually where security and validation occur).
In most systems, the Single Responsibility Principle would suggest that while business logic must occur at the controller level, it shouldn't actually occur in the controller class. Typically, business logic is done in a service, usually injected into the controller. The controller invokes the service with data from the model, gets a result that goes into the model (or a different model), and invokes the view to render it.
So in answer to your question, following "best practices" (and I'll put that in quotes because there's a lot of opinions out there and it's not a black and white proposition), your controller should not be processing and parsing data, and neither should your model; it should be invoking the service that processes and parses the data, then returning the results of aforementioned invocation.
Now... is it necessary to do that in a service? No. You may find it more appropriate, given the size and complexity of your application (i.e. small and not requiring regular maintenance and updates) to take some shortcuts and put the business logic into the controller or the model; it's not like it won't work. If you are following or intend to follow the intent of the Separation of Concerns and SOLID principles, however (and it's a good idea on larger, more complex projects), it's best to refactor that out.
Back to the old concept of decomposing the project logic as Models and Business Logic and the Data Access Layer.
Models was the very thin layer to represent the objects
Business Logic layer was for validations and calling the methods and for processing the data
Data Access Layer for connecting the database and to provide the OR relation
in the MVC, and taking asp.net/tutorials as reference:
Models : to store all the object structure
View: is like an engine to display the data was sent from the controller ( you can think about the view as the xsl file of the xml which is models in this case)
Controller: the place where you call the methods and to execute the processes.
usually you can extend the models to support the validations
finally, in my opinion and based on my experience, most of the sensitive processes that take some execution time, I code it on the sql server side for better performance, and easy to update the procedures in case if any rule was injected or some adjustments was required, all mentioned can be done without rebuilding your application.
I hope my answer gives you some hints and to help you
If your CSV processing is used in more than one place, you can use a CI library to store the processing function. Or you can create a CSV model to store the processing function. That is up to you. I would initially code this in the controller, then if needed again elsewhere, that is when I would factor it out into a library.
Traditionally, models interact with the database, controllers deal with the incoming request, how to process it, what view to respond with. That leaves a layer of business logic (for instance your CSV processing) which I would put in a library, but many would put in its own model.
There is no hard rule about this. MVC, however it was initially proposed, is a loose term interpreted differently in different environments.
Personally, with CI, I use thin controllers, fat models that also contain business logic, and processing logic like CSV parsing I would put in a library, for ease of reuse between projects.
I have gone through a number of videos and tutorials for understanding the difference between Model And Controller.
So what i understood is like controller is the medium between our view and Model , it captures the action performed on the UI and calls the appropriate model class, receives back the model object from the model class and send it to the view given by the view resolver.
Now my question is why do we make the controller to send the request to a model , why do we even need a different class(model). Can't we do the same thing in controller itself ?
It is easier to test and maintain / change / exchange.
The general idea behind MVC is so that you have different modules of your app each with their own function. This way you get less coupling and higher cohesion - coupling refers to classes connected so tightly that, if you decide to change one single variable in one single class you would have to go through your code and check everywhere for exceptions/bugs etc. Cohesion on the other hand refers to having smaller portions of code in separate classes, which depend on nothing else, thus when you change them you can be sure nothing else breaks.
Of course, this can not be explained in a few lines. The best thing you can do is to start writing code, some basic app and see the how it goes.
Really what you say you can do, but it is a bad practice, the MVC is made to separate the layers of development, thus to make it neater develop for all, it must meet a standard for good understanding and management not only but you Developer ...
After writing a few lesser programs when learning Java the way I've designed the programs is with Model-View-Control. With using MVC I have a plethora of getter methods in the model for the view to use.
It feels that while I gain on using MVC, for every new value added I have to add two new methods in the model which quickly get all cluttered with getter & setters.
So I was thinking, maybe I should use the notifyObserver method that takes an argument. But wouldn't feel very smart to send every value by itself either so I figured, maybe if I send a kind of container with all the values, preferably only those that actually changed.
What this would accomplish would be that instead of having a whole lot of getter methods I could just have one method in the model which put all relevant values in the container.
Then in the view I would have a method called from the update which extracted the values from the container and assigning them to the correct fields.
I have two questions concerning this.
First: is this actually a viable way to do this. Would you recommend me doing something along these lines?
Secondly: if I do use this plan and I don't want to keep sending fields that didn't actually change. How would I handle that without having to have if statements to check if the value is not null for every single value?
I've more familiar with the MVP paradigm, but hopefully they're similar enough to comment. While getters (and setters) in and of themselves are not necessarily evil, they are sometimes a sign that your subsystems are too strongly coupled. One really great way to decouple this is to use an event bus: see Best practices for architecting GWT apps. This allows the view to just shoot off events for the controller to listen for whenever something important happens, and the view can listen for events whenever something changes in the model that corresponds to updating the view. Ideally you wouldn't even need to ever pass the model to the view, if you can break up any changes into incremental pieces and just tell the view to change this part and then this other part.
If you feel you have too many getters (and setters) in your model class, maybe you have too many fields altogether. Is it possible that there are several distinct classes hiding within your model? If you extract these into separate classes, it may make your model more manageable.
OTOH the associated container you are thinking about could also be viable - but then why duplicate all data? You could instead use the associated container directly in the model to store all properties you can think of. And you can also pass this around for observers to get updates (preferably wrapped into an unmodifiable container, of course) - although in this setup you wouldn't need to.
In general, Java is a verbose language which expects you to put all those getters and setters (and a lot more) in place. However, any decent IDE can generate those for you with a few keypresses. Note also that you need to write them only once, and you will read and call them many many more times. Verbose also means easily readable.
If you have too many getter it's ok. But you shouldn't need the setter. The view is supposed to only read/query the model.
The MVC pattern should promote something that is asymmetric: the control update the model by calling methods in the model that embed the logic and update the sate accordingly; this respects encapsulation. The view reads/queries the model via the getters. This goes a bit against information hiding, but that's how MVC works.
I wouldn't personally pass all information in the events. It sounds complicated to me: either you end up with something that is not statically typed (e.g. you pass hashmaps), or with a plethora of typed events. I would stick with something simple, and have (possibly many) getter in the model.