I'm working on ASP.NET MVC application & have a quick design question for you.
So I need to implement a common functionality for all my controllers (well, most of them).
I don't want to repeat the same logic in all the controllers.
What'd be the ideal approach in the best interest of MVC?
I found people saying create base controller and inherit it in your controllers. But when I visualize a controller, I can see it'd contain only action methods that return some content/views - Correct me if I'm wrong.
OneController
{
ActionMethod A1
{
//Code to return list of objects for the given integer value. So it calls database stored procedure.
}
}
...multiple such controllers are there.
I'd still like to have A1 exists in the OneController, just put its logic somewhere common place.
Also some people suggest to create just plain Helper class to place the common method.
Could you please suggest me what approach will be better (Or any other appropriate approach)? Thanks.
I agree with you that, most of the times, it only makes sense to inherit from base controllers when we're talking about Actions or methods that are really related. But of course, you can just use base controllers for everything. Your choice.
Other than that, you have 2 options. For classes that have little to no chance of being polymorphic (change behavior depending on the implementation), you are fine to create static classes and just use them inside your controllers. An example would be a class that does math calculations, these are not that polymorphic by nature.
For all the other cases, I'd strongly suggest that you use dependency injection. One of the reasons being that unit testing will become way easier. Here's a guide on how to do it for MVC 4 onwards using the built in engine: https://www.asp.net/mvc/overview/older-versions/hands-on-labs/aspnet-mvc-4-dependency-injection. If you don't want to use it and use Ninject or Simple Injector, you can implement your own ControllerActivator and use Ninject, for instance, to get an instance of your controller.
When using dependency injector, normally your controller would get the dependencies in the constructor, like this:
public class StoreController : Controller
{
private IStoreService service;
public StoreController(IStoreService service)
{
// service in an injected dependency
this.service = service;
}
}
For more information, Google ASP.NET dependency injection.
Related
I'm new to asp.net mvc world mostly a windows developer moving to web. Be nice...
I found ridiculous when I look at many examples of asp.net mvc web applications that the pass to their controllers a list of services
Like this
public CustomerController(ICustomerService customerService,
IAnotherService anotherService,
IYetAnotherService yetAnotherService,
IYetAgainAnotherService yetAgainAnotherService,
etc...
Would not be better to do something like
public CustomerController(IServices services)
{
}
public interface IServices
{
ICustomerService CustomerService{get;set;}
IAnotherServiceService AnotherService{get;set;}
IYetAnotherServiceService YetAnotherServiceService{get;set;}
}
Am I missing the obvious?
As anybody implemented the way I suggest in mvc4 or mvc5. I know mvc6 does it.
But I cannot use mvc6 at work.
Any samples using DI?
Thanks
What you're missing here is the fact that constructors with many parameters is a code smell often caused by that class having to many responsibilities: it violates the Single Responsibility Principle.
So instead of packaging the services to inject into a 'container' class that allows those services to be accessible using a public property, consider the following refactorings:
Divide the class into multiple smaller classes.
Extract logic that implements cross-cutting concerns (such as logging, audit trailing, validation, etc, etc)out of the class and apply those cross-cutting concerns using decorators, global filters (MVC) or message handlers (Web API). A great pattern for your business logic is the command/handler pattern.
Extract logic that uses multiple dependencies out of the class and hide that logic behind a new abstraction that does not expose the wrapped dependencies. This newly created abstraction is called an Aggregate Service.
I agree that for readability sake, even if you have multiple existing services which are also used in other applications, you could always wrap them in another class to avoid passing a long list of dependencies to the controllers.
When you have code in the API controllers that look like this:
public CustomerController(ICustomerService customerService,
IAnotherService anotherService,
IYetAnotherService yetAnotherService,
IYetAgainAnotherService yetAgainAnotherService,
...
That can be a code-smell and is an opportunity to refactor. But this does not mean the original code was a bad design. What I mean is in the API layer, we try not to clutter it with too many services that the controller is dependent on. Instead you can create a facade service. So in your example above, you refactor it to look like this:
public CustomerController(IServices services)
{
}
public interface IServices
{
ICustomerService CustomerService{get;set;}
IAnotherServiceService AnotherService{get;set;}
IYetAnotherServiceService YetAnotherServiceService{get;set;}
}
Which is good and then you can move the IServices to your service/business layer. The concrete implementation of that in the service/business layer will look like this:
public class AConcreteService:IServices {
public AConcreteService(ICustomerService cs, IAnotherServiceService as, IYetAnotherServiceService yas)
{
...
}
public List<Customer> GetCustomers(){
return _cs.GetCustomers();
}
public List<string> GetAnotherServiceData(){
return _as.AnotherServiceData();
}
public List<string> GetYetAnotherServiceData(){
return _yas.YetAnotherServiceData();
}
...
So that code will end up looking like your original code when implemented directly in the controller but is now in the service/business layer. This time it will be easy to unit test in the service class and the API layer will look much cleaner.
I'm practicing DDD with ASP.NET MVC and come to a situation where my controllers have many dependencies on different services and repositories, and testing becomes very tedious.
In general, I have a service or repository for each aggregate root. Consider a page which will list a customer, along with it's orders and a dropdown of different packages and sellers. All of those types are aggregate roots. For this to work, I need a CustomerService, OrderService, PackageRepository and a UserRepository. Like this:
public class OrderController {
public OrderController(Customerservice customerService,
OrderService orderService, Repository<Package> packageRepository,
Repository<User> userRepository)
{
_customerService = customerService
..
}
}
Imagine the number of dependencies and constructor parameters required to render a more complex view.
Maybe I'm approaching my service layer wrong; I could have a CustomerService which takes care of all this, but my service constructor will then explode. I think I'm violating SRP too much.
I think I'm violating SRP too much.
Bingo.
I find that using a command processing layer makes my applications architecture cleaner and more consistent.
Basically, each service method becomes a command handler class (and the method parameters become a command class), and every query is also its own class.
This won't actually reduce your dependencies - your query will likely still require those same couple of services and repositories to provide the correct data; however, when using an IoC framework like Ninject or Spring it won't matter because they will inject what is needed up the whole chain - and testing should be much easier as a dependency on a specific query is easier to fill and test than a dependency on a service class with many marginally related methods.
Also, now the relationship between the Controller and its dependencies is clear, logic has been removed from the Controller, and the query and command classes are more focused on their individual responsibilities.
Yes, this does cause a bit of an explosion of classes and files. Employing proper Object Oriented Programming will tend to do that. But, frankly, what's easier to find/organize/manage - a function in a file of dozens of other semi-related functions or a single file in a directory of dozens of semi-related files. I think that latter hands down.
Code Better had a blog post recently that nearly matches my preferred way of organizing controllers and commands in an MVC app.
Well you can solve this issue easily by using the RenderAction. Just create separate controllers or introduce child actions in those controllers. Now in the main view call render actions with the required parameters. This will give you a nice composite view.
Why not have a service for this scenario to return a view model for you? That way you only have one dependency in the controller although your service may have the separate dependencies
the book dependency injection in .net suggests introducing "facade services" where you'd group related services together then inject the facade instead if you feel like you have too many constructor parameters.
Update: I finally had some available time, so I ended up finally creating an implementation for what I was talking about in my post below. My implementation is:
public class WindsorServiceFactory : IServiceFactory
{
protected IWindsorContainer _container;
public WindsorServiceFactory(IWindsorContainer windsorContainer)
{
_container = windsorContainer;
}
public ServiceType GetService<ServiceType>() where ServiceType : class
{
// Use windsor to resolve the service class. If the dependency can't be resolved throw an exception
try { return _container.Resolve<ServiceType>(); }
catch (ComponentNotFoundException) { throw new ServiceNotFoundException(typeof(ServiceType)); }
}
}
All that is needed now is to pass my IServiceFactory into my controller constructors, and I am now able to keep my constructors clean while still allowing easy (and flexible) unit tests. More details can be found at my blog blog if you are interested.
I have noticed the same issue creeping up in my MVC app, and your question got me thinking of how I want to handle this. As I'm using a command and query approach (where each action or query is a separate service class) my controllers are already getting out of hand, and will probably be even worse later on.
After thinking about this I think the route I am going to look at going is to create a SerivceFactory class, which would look like:
public class ServiceFactory
{
public ServiceFactory( UserService userService, CustomerService customerService, etc...)
{
// Code to set private service references here
}
public T GetService<T>(Type serviceType) where T : IService
{
// Determine if serviceType is a valid service type,
// and return the instantiated version of that service class
// otherwise throw error
}
}
Note that I wrote this up in Notepad++ off hand so I am pretty sure I got the generics part of the GetService method syntactically wrong , but that's the general idea. So then your controller will end up looking like this:
public class OrderController {
public OrderController(ServiceFactory factory) {
_factory = factory;
}
}
You would then have IoC instantiate your ServiceFactory instance, and everything should work as expected.
The good part about this is that if you realize that you have to use the ProductService class in your controller, you don't have to mess with controller's constructor at all, you only have to just call _factory.GetService() for your intended service in the action method.
Finally, this approach allows you to still mock services out (one of the big reasons for using IoC and passing them straight into the controller's constructor) by just creating a new ServiceFactory in your test code with the mocked services passed in (the rest left as null).
I think this will keep a good balance out the best world of flexibility and testability, and keeps service instantiation in one spot.
After typing this all out I'm actually excited to go home and implement this in my app :)
I tend to consume the same set of repositories from all my controllers. That is, I instantiate repository objects (with IoC) in every controller.
I think I could derive my controllers from a base controller that could instantiate these objects in one place. Could you point me to the right of doing this? Thank you for your help.
You have a number of options, and which one is "the right way" is really up to you and how your system functions overall. There could be performance issues for various instantiated objects that need to be considered, etc.
One option could be as simple as:
public class BaseController
{
protected ISomeRepository myRepository = IoCContainer.Resolve<ISomeRepository>();
}
public class MyController : BaseController { }
Additionally, you could move the initialization to the base controller's constructor rather than have it be inline like that.
Another option might be to late-bind the repositories, if having them all incurs a performance hit (weighed carefully with the hit of instantiating them) and on average they aren't always needed:
public class BaseController
{
private ISomeRepository _myRepository;
protected ISomeRepository myRepository
{
get
{
if (_myRepository == null)
_myRepository = IoCContainer.Resolve<ISomeRepository>();
return _myRepository;
}
}
}
There are probably more options available to you, it all depends on your setup. How your particular IoC container works may also play heavily into your design decision.
(Note that I reference the IoCContainer directly here for brevity and simplicity, but I recommend abstracting out the container behind a service locator so that you don't have so many references to the container itself.)
Actually, it depends on what kind of tasks should those "Common Repositories" complete. If they are directly relate to what Action supposed to do - maybe that is okay. But you'll anyway face some problems with IoC-resolution. In order to avoid injecting those repositories all the time for each new Repo you'll have to make a dependency on Service Locator in your base controller. Which isn't good thing.
If those Repositories are ther efor something that is orthogonal to what Action is going to do - then it is more like AOP-kinda logic, so I'd better use Action Filters for that or RenderAction.
In common case, I'd try to avoid layer supertype dependencies as well as would prefer Composition over Inheritance.
In the real world, Controllers can potentially need to use data from a variety of database tables and other data stores. For example:
[Authorize]
public class MembersController : Controller
{
ICourseRepository repCourse;
IUserCourseRepository repUserCourse;
IMember member;
public MembersController(ICourseRepository repCourse, IUserCourseRepository repUserCourse, IMember member)
{
this.repCourse = repCourse;
this.repUserCourse = repUserCourse;
this.member = member;
}
So:
Should I use a repository for each table?
I guess this is where the concept of agregates comes into play? Should I have one Repository per aggregate?
Do I just add as many Repositories as I need to the constructor of the Controller?
Is this a sign that my design is wrong?
NOTE:
The IMember interface essentially represents a helper object that puts a nice face on the Membership provider. Ie, it puts all the code in one place. For example:
Guid userId;
public Guid UserId
{
get
{
if (userId == null)
{
try
{
userId = (Guid) Membership.GetUser().ProviderUserKey;
}
catch { }
}
return userId;
}
}
One problem with that is surely caching this kind of output. I can feel another question coming on.
EDIT:
I'm using Ninject for DI and am pretty sold on the whole DI, DDD and TDD thing. Well, sort of. I also try to be a pragmatist...
1. Should I use a repository for each table?
Probably not. If you have a repository per table, you are essentially doing Active Record. I also personally prefer to avoid calling these classes "Repository" because of the confusion that can occur between Domain Driven Design's concept of a "Repository" and the class-per-table "Repository" that seems to have become commonly used with Linq2SQL, SubSonic, etc. and many MVC tutorials.
2. I guess this is where the concept of agregates comes into play? Should I have one Repository per aggregate?
Yes and yes. If you are going to go this route.
'3.' Do I just add as many Repositories as I need to the constructor of the Controller?
I don't let my controllers touch my repositories directly. And I don't let my Views touch my domain classes directly, either.
Instead, my controllers have Query classes that are responsible for returning View Models. The Query classes reference whatever repositories (or other sources of data) they need to compile the View Model.
Well #awrigley, here is my advise:
Q: Should I use a repository for each table?
A: No, as you mentioned on question 2. use a repository per aggregate and perform the operations on aggregate root only.
Q: Do I just add as many Repositories as I need to the constructor of the Controller?
A: I guess you´re using IoC and constructor-injection, well, in this case, make sure you only pass real dependencies. this post may help you decide on this topic.
(pst! that empty catch is not a nice thing!!) ;)
Cheers!
This all depends on how "Domain Driven Design" your going to be. Do you know what an Aggregate Root is? Most of the time a generically typed repository that can do all your basic CRUD will suffice. Its only when you start having thick models with context and boundaries that this starts to matter.
I'm trying to think of a good way to clean up my controllers to make them more testable without having to rely on a constant database connection. I thought I had a decent start by abstracting away my object context with an IObjectContext. This works well for the context, but my next problem is that I have a generic repository that I use in a number of action methods throughout my project (see code below).
In addition to the default constructor, my controller consists of an overload, which accepts an IObjectContext (simple dependency injection). In my unit tests, I can easily mock the IObjectContext. My issue is dealing with my generic repository in various action methods. I could add a number of additional constructor overloads to the controller, but I'm afraid this would get messy, really quickly. Short of doing that, however, I simply haven't been able to think of a clean way to improve testability so that I don't have to rely on a database connection.
Is there a simple solution that I'm overlooking?
/// <summary>
/// Initializes a new instance of the HomeController class
/// </summary>
public HomeController(IObjectContext context)
{
_context = context;
}
/// <summary>
/// GET: /home/index
/// </summary>
/// <returns>Renders the home page</returns>
public ActionResult Index()
{
List contacts;
HomeViewModel model;
using (IRepository<Contact> repository = new DataRepository<Contact>(_context))
{
contacts = new List(repository.GetAll());
}
model = new HomeViewModel(contacts);
return View(model);
}
If I have to go the route of adding additional constructor overloads to accommodate my concerns, I was considering adding a number of private properties (which would deffer instantiation of the repositories until they are needed) to my controllers for each of the repositories that action methods make use of. For example:
private IRepository<Contact> _contactRepository;
private IRepository<Contact> ContactRepository
{
get
{
return _contactRepository ?? (_contactRepository = new DataRepository<Contact>());
}
}
For unit testing purposes, I'd be able to pre-initialize the repositories using the constructor overloads.
What are your thoughts on this? Am I missing something cleaner that should be obvious?
First of all, get rid of your current Bastard Injection constructor overloads. With DI, you should only need one constructor, and that's the one that takes all the dependencies. (To enable the ASP.NET MVC run-time to create the Controllers, implement a custom IControllerFactory.)
The next step is to inject all your dependencies through the constructor. When you think it gets messy because there are too many constructor parameters, it's a good sign that you are violating the Single Responsibility Principle. When that happens, you extract an Aggregate Service.
Rinse and repeat :)
Well, I do what your final example shows all the time to inject mocks into my controllers. It does have a little smell to it (designing for testability), but it isn't bad coding and works great for testing.
Your use of a generic repository is more a dependency-cloaking device than a dependency injection. You should be able to see all of the dependencies a particular Controller uses: a generic repository hides this fact somewhere deep in the entrails of your Controllers which makes maintaining (and unit-testing) the code much more difficult. My suggestion: use concrete repositories.
You could also take a look at domain-driven design stuff.