I am trying to understand single responsibility principle. I have following questions.
The Single Responsibility Principle (SRP) states that there should never be
more than one reason for a class to change.
Usually our Resource,Service and Repository classes have
create,read,update and delete method. We are changing each class to
modify code for any any of these operations. Is it violating SRP? Do we need
separate class for each action?
When I run sonar lint, I have seen below message.
Classes should not coupled to too many other classes.
Here I am injecting other classes using spring DI. Is there any limit on
number of dependencies?
I may be missing crux of this concept. Please suggest a good resource for understanding this concept better with examples
The SRP states that the class should only do one thing, like persisting entities in the case of repositories. I guess that you've confused "class" and "object" here: if you have several methods that could change the object's state this could be in accordance with the SRP. However the only reason for a repository class to change should have something to do with its purpose, namely persisting or retrieving entities in this case.
The Wikipedia article about the Single Responsibility Principle puts it very well.
To your second point: there is no such thing as a maximum number of dependencies a class can have, but it could be a sign for a design weakness if there are many of them.
The Single Responsibility Principle (SRP) states that there should
never be more than one reason for a class to change.
The Single Responsibility principle doesn't mean a single method or a single type of action by component/class.
It means a single responsibility in the scope of a matter.
Persistence operations makes part of the same matter.
So putting all of them in a single class doesn't violate necessary the principle.
Now if you have dozen and dozen of specific database operations, it would make sense to divide them into distinct classes having a well defined responsibility such as selecting operations, updating operations, and so for.
Usually our Resource,Service and Repository classes have
create,read,update and delete method. We are changing each class to
modify code for any any of these operations. Is it violating SRP?
These are distinct layers.
If you change the model of a layer, others are very often impacted as data passes between layers.
It is like if you add an information in your database, you necessary need to change your GUIs and your processing if you want see/manipulate them.
Now if you change implementation of layers, other layers should have no or very few consequences.
Related
I have a lot of regex functions that validates the data.
They have a common domain. Where to place them, in service, helper wherelse?
As I know to place it in controller is not good idea, because it is not reusable.
Regex are more close to utility functions. In fact, utilities methods can be used anywhere depending upon the requirements. Therefor, these must be independent to any entity/models, controller or any class in Laravel.
Further, your question is closely connected with software engineering concept known as Coupling vs Cohesion
Coupling is defined as the degree of interdependence between the modules and Cohesion is defined as the degree of relationship between elements of the same module.
So a good software design says that there must always be low coupling and high cohesion.
Therefor, I believe if we create Regex utility module then it should work independently of any module/class/model/controller. They must have least dependency between each other to have low coupling as much as possible. Chances are higher that methods you define in Regex module will reuse across the other controllers/classes.
On the other hand, if you define Regex related methods inside controller or a model, then their inter module dependency will increase and chances are we will not be able to reuse these regex related methods anymore.
Therefor, a good idea is to isolate modules from each other that have no particular dependency and will reuse across the other modules.
In Laravel, we generally create Helper class/methods to achieve this. So you can defiantly go with Helper classes approach. Create a Regex Helper class and reuse it in whole application.
Cheers :)
I'm working with Laravel 5 but I think this question can be applied beyond the scope of a single framework or language. The last few days I've been all about writting interfaces and implementations for repositories, and then binding services to the IoC and all that stuff. It feels extremely slow.
If I need a new method in my service, say, Store::getReviews() I must create the relationship in my entity model class (data source, in this case Eloquent) then I must declare the method in the repo interface to make it required for any other implementation, then I must write the actual method in the repo implementation, then I have to create another method on the service that calls on the repo to extract all reviews for the store... (intentional run-on sentence) It feels like too much.
Creating a new model now isn't as simple as extending a base model class anymore. There are so many files I have to write and keep track of. Sometimes I'll get confused as of to where exactly I should put something, or find halfway throught setting up a method that I'm in the wrong class. I also lost Eloquent's query building in the service. Everytime I need something that Eloquent has, I have to implement it in the repo and the service.
The idea behind this architecture is awesome but the actual implementation I am finding extremely tedious. Is there a better, faster way to do things? I feel I'm beeing too messy, even though I put common methods and stuff in abstract classes. There's just too much to write.
I've wrestled with all this stuff as I moved to Laravel 5. That's when I decided to change my approach (it was tough decision). During this process I've come to the following conclusions:
I've decided to drop Eloquent (and the Active Record pattern). I don't even use the query builder. I do use the DB fascade still, as it's handy for things like parameterized query binding, transactions, logging, etc. Developers should know SQL, and if they are required to know it, then why force another layer of abstraction on them (a layer that cannot replace SQL fully or efficiently). And remember, the bridge from the OOP world to the Relational Database world is never going to be pretty. Bear with me, keeping reading...
Because of #1, I switched to Lumen where Eloquent is turned off by default. It's fast, lean, and still does everything I needed and loved in Laravel.
Each query fits in one of two categories (I suppose this is a form of CQRS):
3.1. Repositories (commands): These deal with changing state (writes) and situations where you need to hydrate an object and apply some rules before changing state (sometimes you have to do some reads to make a write) (also sometimes you do bulk writes and hydration may not be efficient, so just create repository methods that do this too). So I have a folder called "Domain" (for Domain Driven Design) and inside are more folders each representing how I think of my business domain. With each entity I have a paired repository. An entity here is a class that is like what others may call a "model", it holds properties and has methods that help me keep the properties valid or do work on them that will be eventually persisted in the repository. The repository is a class with a bunch of methods that represent all the types of querying I need to do that relates to that entity (ie. $repo->save()). The methods may accept a few parameters (to allow for a bit of dynamic query action inside, but not too much) and inside you'll find the raw queries and some code to hydrate the entities. You'll find that repositories typically accept and/or return entities.
3.2. Queries (a.k.a. screens?): I have a folder called "Queries" where I have different classes of methods that inside have raw queries to perform display work. The classes kind of just help for grouping together things but aren't the same as Repositories (ie. they don't do hydrating, writes, return entities, etc.). The goal is to use these for reads and most display purposes.
Don't interface so unnecessarily. Interfaces are good for polymorphic situations where you need them. Situations where you know you will be switching between multiple implementations. They are unneeded extra work when you are working 1:1. Plus, it's easy to take a class and turn it into an interface later. You never want to over optimize prematurely.
Because of #4, you don't need lots of service providers. I think it would be overkill to have a service provider for all my repositories.
If the almost mythological time comes when you want to switch out database engines, then all you have to do is go to two places. The two places mentioned in #3 above. You replace the raw queries inside. This is good, since you have a list of all the persistence methods your app needs. You can tailor each raw query inside those methods to work with the new data-store in the unique way that data-store calls for. The method stays the same but the internal querying gets changed. It is important to remember that the work needed to change out a database will obviously grow as your app grows but the complexity in your app has to go somewhere. Each raw query represents complexity. But you've encapsulated these raw queries, so you've done the best to shield the rest of your app!
I'm successfully using this approach inspired by DDD concepts. Once you are utilizing the repository approach then there is little need to use Eloquent IMHO. And I find I'm not writing extra stuff (as you mention in your question), all while still keeping my app flexible for future changes. Here is another approach from a fellow Artisan (although I don't necessarily agree with using Doctrine ORM). Good Luck and Happy Coding!
Laravel's Eloquent is an Active Record, this technology demands a lot of processing. Domain entities are understood as plain objects, for that purpose try to utilizes Doctrime ORM. I built a facilitator for use Lumen and doctrine ORM follow the link.
https://github.com/davists/Lumen-Doctrine-DDD-Generator
*for acurated perfomance analisys there is cachegrind.
http://kcachegrind.sourceforge.net/html/Home.html
I'm starting to develop website that use the spring framework.I have three controller.There are newCustomerController,editCustomerController and deleteCustomerController.These controllers are mapped with view that use for create update and delete, but I create only customer.
So, I would like to know.Is it appropriate to declare the controllers like this.
Thank
The answer to this question is subjective and maybe more a topic for https://softwareengineering.stackexchange.com/. However, there is something very spring related about it that I would like to comment.
There are a few principles that attempt at guiding developers of how to strike a good balance when thinking about designing the classes. One of those is the Single responsibility principle.
In object-oriented programming, the single responsibility principle
states that every class should have a single responsibility, and that
responsibility should be entirely encapsulated by the class. All its
services should be narrowly aligned with that responsibility
A catchier explanation is
A class or module should have one, and only one, reason to change.
However, its still often hard to reason about it properly.
Nevertheless, Spring gives you means for it (think of this statement as a poetic freedom of interpretation). Embrace constructor based dependency injection. There are quite a few reasons why you should consider constructor based dependency injection, but the part relevent to your question is adressed in the quote from the blog
An often faced argument I get is: “Constructors just get too verbose
if I have 6 or 7 dependencies. With fields only, this is fine”.
Awesome, you’ve effectively worked around a clear indicator that the
code you write is doing way too much. An increase in the number of
dependencies a type has should hurt, as it makes you think about
whether you should split up the component into multiple ones.
In other words, if you stick to constructor based injection, and your constructor turns a bit ugly, the class is most likely doing too much and you should consider redesigning.
The same works the other way around, if your operations are a part of the logical whole (like CRUD operations), and they use the same dependencies (now "measurable" by the count and the type of the injected deps) with no clear ideas of what can cause the operations to evolve independently of each other, than no reason to split to separate classes/components.
It should be better if you define one controller for Customer class and in that class you should have all methods related to customer operations (edit,delete,create and read).
A few general questions to those who are well-versed in developing web-based applications.
Question 1:
How do you avoid the problem of "dependency carrying"? From what I understand, the first point of object retrieval should happen in your controller's action method. From there, you can use a variety of models, classes, services, and components that can require certain objects.
How do you avoid the need to pass an object to another just because an object it uses requires it? I'd like to avoid going to the database/cache to get the data again, but I also don't want to create functions that require a ton of parameters. Should the controller action be the place where you create every object that you'll eventually need for the request?
Question 2:
What data do you store in the session? My understanding is that you should generally only store things like user id, email address, name, and access permissions.
What if you have data that needs to be analyzed for every request when a user is logged in? Should you store the entire user object in the cache versus the session?
Question 3:
Do you place your data-retrieval methods in the model itself or in a separate object that gets the data and returns a model? What are the advantages to this approach?
Question 4:
If your site is driven by a user id, how do you unit test your code base? Is this why you should have all of your data-retrieval methods in a centralized place so you can override it in your unit tests?
Question 5:
Generally speaking, do you unit test your controllers? I have heard many say that it's a difficult and even a bad practice. What is your opinion of it? What exactly do you test within your controllers?
Any other tidbits of information that you'd like to share regarding best practices are welcome! I'm always willing to learn more.
How do you avoid the problem of "dependency carrying"?
Good object oriented design of a BaseController SuperClass can handle a lot of the heavy lifting of instantiating commonly used objects etc. Usage of Composite types to share data across calls is a not so uncommon practice. E.g. creating some Context Object unique to your application within the Controller to share information among processes isn't a terrible idea.
What data do you store in the session?
As few things as is humanly possible.
If there is some data intensive operation which requires a lot of overhead to process AND it's required quite often by the application, it is a suitable candidate for session storage. And yes, storage of information such as User Id and other personalization information is not a bad practice for session state. Generally though the usage of cookies is the preferred method for personalization. Always remember though to never, ever, trust the content of cookies e.g. properly validate what's read before trusting it.
Do you place your data-retrieval methods in the model itself or in a separate object that gets the data and returns a model?
I prefer to use the Repository pattern for my models. The model itself usually contains simple business rule validations etc while the Repository hits a Business Object for results and transformations/manipulations. There are a lot of Patterns and ORM tools out in the market and this is a heavily debated topic so it sometimes just comes down to familiarity with tools etc...
What are the advantages to this approach?
The advantage I see with the Repository Pattern is the dumber your models are, the easier they are to modify. If they are representatives of a Business Object (such as a web service or data table), changes to those underlying objects is sufficiently abstracted from the presentation logic that is my MVC application. If I implement all the logic to load the model within the model itself, I am kind of violating a separation of concerns pattern. Again though, this is all very subjective.
If your site is driven by a user id, how do you unit test your code base?
It is highly advised to use Dependency Injection whenever possible in code. Some IoC Containers take care of this rather efficiently and once understood greatly improve your overall architecture and design. That being said, the user context itself should be implemented via some form of known interface that can then be "mocked" in your application. You can then, in your test harness, mock any user you wish and all dependent objects won't know the difference because they will be simply looking at an interface.
Generally speaking, do you unit test your controllers?
Absolutely. Since controllers are expected to return known content-types, with the proper testing tools we can use practices to mock the HttpContext information, call the Action Method and view the results to see they match our expectations. Sometimes this results in looking only for HTTP status codes when the result is some massive HTML document, but in the cases of a JSON response we can readily see that the action method is returning all scenario's information as expected
What exactly do you test within your controllers?
Any and all publicly declared members of your controller should be tested thoroughly.
Long question, longer answer. Hope this helps anyone and please just take this all as my own opinion. A lot of these questions are religious debates and you're always safe just practicing proper Object Oriented Design, SOLID, Interface Programming, DRY etc...
Regarding dependency explosion, the book Dependency Injection in .NET (which is excellent) explains that too many dependencies reveals that your controller is taking on too much responsibility, i.e. is violating the single responsibility principle. Some of that responsibility should be abstracted behind aggregates that perform multiple operations.
Basically, your controller should be dumb. If it needs that many dependencies to do its job, it's doing too much! It should just take user input (e.g. URLs, query strings, or POST data) and pass along that data, in the appropriate format, to your service layer.
Example, drawn from the book
We start with an OrderService with dependencies on OrderRepository, IMessageService, IBillingSystem, IInventoryManagement, and ILocationService. It's not a controller, but the same principle applies.
We notice that ILocationService and IInventoryManagement are both really implementation details of an order fulfillment algorithm (use the location service to find the closest warehouse, then manage its inventory). So we abstract them into IOrderFulfillment, and a concrete implementation LocationOrderFulfillment that uses IInventoryManagement and ILocationService. This is cool, because we have hidden some details away from our OrderService and furthermore brought to light an important domain concept: order fulfillment. We could implement this domain concept in a non-location-based way now, without having to change OrderService, since it only depends on the interface.
Next we notice that IMessageService, IBillingSystem, and our new IOrderFulfillment abstractions are all really used in the same way: they are notified about the order. So we create an INotificationService, and make MessageNotification a concrete implementation of both INotificationService and IMessageService. Similarly for BillingNotification and OrderFulfillmentNotification.
Now here's the trick: we create a new CompositeNotificationService, which derives from INotificationService and delegates to various "child" INotificationService instances. The concrete instance we use to solve our original problem will delegate in particular to MessageNotification, BillingNotification, and OrderFulfillmentNotification. But if we wish to notify more systems, we don' have to go edit our controller: we just have to implement our particular CompositeNotificationService differently.
Our OrderService now depends only on OrderRepository and INotificationService, which is much more reasonable! It has two constructor parameters instead of 5, and most importantly, it takes on almost no responsibility for figuring out what to do.
Warning acronym overload approaching!!! I'm doing TDD and DDD with an MVP passive view pattern and DI. I'm finding myself adding dependency after dependency to the constructor of my presenter class as I write each new test. Most are domain objects. I'm using factories for dependency injection though I will likely be moving to an IoC container eventually.
When using constructor injection (as apposed to property injection) its easy to see where your dependencies are. A large number of dependencies is usually an indicator that a class has too much responsibility but in the case of a presenter, I fail to see how to avoid this.
I've thought of wrapping all the domain objects into a single "Domain" class which would act as a middle man but I have this gut feeling that I'd only be moving the problem instead of fixing it.
Am I missing something or is this unavoidable?
Often a large number of arguments to a method (constructor, function, etc) is a code smell. It can be hard to understand what all the arguments are. This is especially the case if you have large numbers of arguments of the same type. It is very easy for them to get confused which can introduce subtle bugs.
The refactoring is called "Introduce Parameter Object". Whether that's really a domain object or not, it is basically a data transfer object that minimizes the number of parameters passed to a method and gives them a bit more context.
I only use DI on the Constructor if I need something to be there from the start. Otherwise I use properties and have lazy loading for the other items. For TDD/DI as long as you can inject the item when you need it you don't need to add it to your constructor.
I recommend always following the Law of Demeter and not following the DI myth of everything needs to be in the constructor. Misko Hevery (Agile Coach at Google) describes it well on his blog http://misko.hevery.com/2008/10/21/dependency-injection-myth-reference-passing/
Having a Layer Supertype might not be a bad idea, but I think your code smell might be indicating something else. Geofflane mentioned the refactor pattern, Introduce Parameter Object. While it's a good pattern for this sort of problem, I'm not entirely sure it's the way to go for this situation.
Question: Why are you passing in Domain Model objects to the constructor?
There is such a thing as having too much abstraction. If there's one solid layer of code you should be able to trust, it's your Domain Model. You don't need to reference 3 IEntity objects when you're dealing with Customer, Vendor, and Product classes if those are part of your basic Domain Model and you don't necessarily need polymorphism.
My advice: Pass in application and domain services. Trust your Domain Model.
EDIT:
Re-reading the problem when it's not horribly late at night, I realize your "Domain class" is already the Introduce Parameter Object refactoring and not, in fact, a Layer Supertype, as I thought at 3AM.
I also realize that perhaps you need to reference the Model objects in the application code, outside the Presenter. Perhaps you're doing some initial setup of your Model objects before passing them in to the Presenter. If this is the case, your "Domain class" idea might be best. If there is some initial setup, when moving to an IoC, you'll want to look at something like Factory Support in Castle Windsor. (Other IoC containers have similar concepts.)