I've been trying to learn how the service layer and repository pattern work. So far I've written a service layer and a simple repository pattern interface. However, I often see articles stating that the repository pattern allows for being able to swap in and out different data stores without the consuming code having to be changed.
In my case I want to be able to support reading and writing the application data to CSV and/or XML files. This is the part where I do not understand how to properly implement this with the repository pattern. Should I have a repository per data store?
ProductCsvRepository : IProductRepository
ProductXmlRepository : IProductRepository
However if I do this then the service layer would have to be aware of the underlying data store, which breaks the idea of being able to easily swap in and out different data stores.
Would I then have to have a service layer that looks like this?
private readonly IProductXmlRepository _productXmlRepository;
private readonly IProductCsvRepository _productCsvRepository;
public ProductService()
{
_productXmlRepository = new IProductXmlRepository();
_productCsvRepository = new IProductCsvRepository();
}
public ICollection<Product> GetAllXml()
{
return _productXmlRepository.GetAllCsv();
}
public ICollection<Product> GetAll()
{
return _productCsvRepository.GetAllXml();
}
This then raises two questions:
Surely this then breaks the idea of the consuming code needing to know what the data store is?
What about in the situations where the consuming code does need to know about the data store, such as for "File > Export As" type functionality? Should export functionality actually be a different service that utilises the appropriate CSV or XML service?
I think I am definetly not understanding how to correctly implement a repository patten and a service layer. How should I actually design repository patten and service layer?
Take a look at dependency injection and the plug-in pattern. They support injecting a concrete implementation of a repository. Your service layer then has only one reference to IProductRepository and a concrete repository gets injected. Something along the lines of this:
public class ProductService
{
private readonly IProductRepository _productRepository;
public ProductService(IProductRepository productRepository)
{
_productRepository = productRepository;
}
}
public class ConsumingClass {
{
private readonly IProductService _productService = new ProductService(new ProductXmlRepository());
// methods to use the the product service
}
But better would be to use a inversion of control container like NInject or SimpleInjector. Those frameworks can be used to link abstract classes (IProductRepository) to concrete classes (ProductXmlRepository or ProductXmlRepository) based on xml configurations.
Your application's solution should be structured following the Dependency Inversion Principle (http://deviq.com/dependency-inversion-principle/), so that there are at minimum three projects:
Core
Infrastructure
Your UI project
All (or nearly all) of your interfaces should be declared in Core (e.g. IProductRepository). Your interface implementations belong in Infrastructure, which references Core. Finally, your UI project should reference Core, but not necessarily Infrastructure (learn how to use types from a project without referencing it: http://blog.falafel.com/use-types-from-project-without-referencing/).
With this architecture in place, you can use dependency injection (http://deviq.com/dependency-injection/) to inject the desired implementation of a given type at runtime, which provides great flexibility and testability.
Setting up your solution with the proper dependencies between projects is critical to being successful with this approach, since a traditional UI -> Business Layer -> Data Layer setup will not allow you to invert dependencies. Once your solution is set up in this manner, you should follow the Explicit Dependencies Principle (http://deviq.com/explicit-dependencies-principle/) in all of your UI and service code.
Related
I am pretty new to Clean Architecture in C#.
Based on the details my understanding was all the business logic must be in Application Layer and any infrastructure level things (DB Crud operations, Message handlings) must be in infrastructure layer.
So I have started the development, but found there is no dependency with infrastructure layer in application layer. Even why they are saying keep the business logic in application layer and infra operations in that layer.
Without that dependency how can I access the CRUD operations in infra layer.
Also there is dependency with Applicaiton layer in infrastructure layer which is I didnt understand.
Someone please help because I really got stuck with it. I have few methods in my application layer and I need to write the output into DB as well, which I dont know how to implement.
So simple it would be like this based on the description
Application Layer
IMessageBroker.cs
Public class IMessageBroker
{
Task<int> pushtoqueue(string queue, string message);
}
myservice.cs
public class myservice
{
public void MyMethod
{
//Here I need to call the pushtoqueue method which I dont know
}
}
Infrastructure Layer
MessageBroker.cs
public class messagebroker :Imessagebroker
{
public task<int> pushtoqueue(string queue, string message)
{
// here the queue pushing code comes
}
}
DependencyInjection.cs
services.Addscoped<IMessageBroker, MessageBroker>();
Please share your thoughts..
Environment
.NET 6
Azure Function Apps 4.0
The sample you linked to uses a concept called "inversion of control" (IoC). Adapted to your sample and defined in a (lengthy) sentence, this concept is about inverting the dependency from the Application layer to the Infrastructure layer so that the Application layer defines its requirements towards the Infrastructure layer (in form of interfaces) and can work with any Infrastructure layer that implements these interfaces.
If you look at the diagram in the overview section, there is an arrow from the Infrastructure layer to the Application layer. This expresses the dependency from the Infrastructure layer on the Application layer.
In your case, the components serve the following purpuse:
IMessageBroker: interface in Application layer that defindes the requirements that the Infrastructure layer has to fulfill.
MyService: service class that uses infrastructure components. An instance of type IMessageBroker should be injected into the class in order to access the message broker.
MessageBroker: concrete implementation of IMessageBroker.
The benefit of this approach is that you can easily replace infrastructure components without changing the application layer. While changing from one message broker to another might be comparatively seldom, being able to use mock objects when testing MyService is invaluable.
To answer the original question: how can you call the pushtoqueue method?
Just inject an instance of IMessageBroker into MyService and use it there:
public class MyService
{
private readonly IMessageBroker _msgBroker;
public MyService(IMessageBroker msgBroker)
{
_msgBroker = msgBroker;
}
public void MyMethod
{
//Here I need to call the pushtoqueue method which I dont know
_msgBroker.PushToQueue("queue", "message");
}
}
In your sample, you already add a registration of IMessageBroker to the IoC container, so the instance is injected when creating MyService.
As a side note: following naming conventions increases readability for fellow programmers. I've changed some of the names from the question. For an overview of the C# naming conventions see this link.
The typical architecture I am using consists of Manager objects in the Business Layer. I am using DI/IOC within .NET Core/ .NET Standard. The managers are injected into the service layer and consequently the services are injected into our API controllers. So I am presently working in a Manager class. I now need a method that resides in another manager class.
Usually I return back through the service layer to the controller, then call the next service and then the manager through that.
I am wondering whether it is OK to just inject a Manager I require directly into the Manager I am working in. Therefore cutting out the trip back to the controller and then back up through the other service to the other manager. Basically I have 2 * Managers.
public class TypeCodeManager : ITypeCodeManager
{
public TypeCodeManager()
{
}
public async Task<int> GetTypeCodeAsync(string typeCode, string code)
}
public class UserManager : IUserManager
{
private readonly ITypeCodeManager _typeCodeManager;
public UserManager(ITypeCodeManager typeCodeManager)
{
_typeCodeManager = typeCodeManager
}
}
Is this generally a good idea?
I would say it's generally not a good idea to cross over into other domains through the "managers", assuming that your managers are what talks to the persistence layer. This will quickly lead to confusing dependency maps and code.
Your services are a much better layer to orchestrate the cross-domain concerns as they may describe cross domain workflows and depend on multiple managers.
I have a plan to rework my company web publishing platform with dependency injection because the coding references start to become a bit more complex.
In my research I have found a lot of examples regarding MVC but our intention at the moment is to rework the web platform's Business logic, DAL, Core etc.. with minimal UI interventions.
The architecture of the web platform is the following
SQL database
DAL (EF6)
Separated model from dal (poco)
Business Logic
CMS System
Front end (websites)
All in all separated projects with their own concerns but heavily referenced in between.
In my research to counteract heavy referencing and coupling I have chosen and followed the following example
techbrij blog post
I do understand the concepts of abstraction and dependency injection well and have set up a test project but hit a snag.
In MVC the instantiating new data class (poco) is handled by the ActionResult
// POST: /Country/Create
[HttpPost]
[ValidateAntiForgeryToken]
public ActionResult Create(Country country)
{
// TODO: Add insert logic here
if (ModelState.IsValid)
{
_CountryService.Create(country);
return RedirectToAction("Index");
}
return View(country);
}
so far so good if we use MVC. But if I use Webforms in order to insert new record my logic says that i need to instantiate a new class from the model fill its properties with specific values and pass it to the BLL/DAL or service layer:
public void InsertRecord()
{
Country country = new Country();
country.Name = "Some Country"; // or value from textbox..
_CountryService.Create(country);
}
My question is:
Regarding webforms, is this OK or do I need to absrtact the model in order to inject the new data class without the "new" keyword
Since using the "new" keyword will not decouple my data model, how would you do this to achieve decoupling/ioc/di?
I think that's fine. All the MVC framework is doing is newing up an instance of Country and matching up request parameters to your model's properties. You might find a library that does the same in webforms but it would probably be overkill.
You could use a factory to abstract away the newing up but it's probably not for situations like you have here.
Take a look at this article. It differentiates between Injectables and Newables.
In my understanding, Injectables are classes that present behavior that you want to vary using DI. While Newables are simple classes that mostly contain data. They might contain some behavior that is internal to these classes (does not require external services to work) so you don't want to change such behavior using DI.
It seems to me that the Country class is a Newable. Therefore, it is perfectly normal to new it up via new.
The link you provided use repository pattern, I personally run away from it because it is all about hide your persistence tools, and if you hide your arsenal you lose the power it provides, apart from the probably unnecessary added complexity.
That said it is ok to manually create entities with new keywords, as long as you don't do it in the user interface class, for web forms you can use Model View Presenter combined with modern Model Binding technics available for Asp.NET Web Forms. Presenter instantiate entities and interacts with persistent mechanisms (EF in your case).
You can decouple UI code from presentation code, presenter can lives in its own assembly and works with View Interfaces so you will inject concrete implementations with IoC.
Here is a very basic sample skeleton for a sample infrastructure representing the above:
public interface IView{}
public abstract Presenter<T> where T : IView
{
public Presenter( T view){ View = view;}
public T View {get;set;}
}
The services I build are about encapsulating Business Logic, Application Logic, etc. Again, you will want have to avoid hard references to concrete implementations of those services by working with interfaces and injecting concrete implementations with some IoC.
I have an application which uses an IPaymentService to process credit card payments. The appropriate implementation (CreditCardPaymentComponent or CheckPaymentComponent or anything else that implements the IPaymentService interface) is injected into the application by a PaymentProvider using the ASP.NET Provider Model.
We also need these components to be reusable for different applications which may not have access to the PaymentProvider.
The question is where to put the IPaymentService interface? It can't be inside the application because there are multiple applications which need to use the service. It can't be inside the service because there are multiple services which implement this interface. I don't like putting the interfaces in their own project because then I have to add references everywhere. Is there another solution?
EDIT: To clarify, the point of using the Provider Model is so we can support other developers, so they can write for example CustomPaymentComponent which implements IPaymentService and it works seamlessly with our app. I am leaning towards #Frazell's answer but I am just wondering if there is any downside to putting IPaymentService in the same assembly with the PaymentComponents? If you had to develop a CustomPaymentComponent for this system, what would make the most sense to you?
You can't escape having to have the interface and the implementation code referenced where it is needed. If the payment code has to be reusable in many applications I would break it out into a separate library (dll) and package it appropriately.
Managing the additional assembly is a lot easier than resorting to code duplication, which is the only alternative. Duplication has to be avoided at all costs.
Depending on what you're doing overall. I would provide the interface and base implementations in the same assembly (such as a payments assembly) and allow use of DI to swap out the implementations where needed in edge case scenarios.
The solution is actually quite simple:
Use the adapter pattern.
You don't let the components implement that interface at all, but implement adapters for each component based on that interface. In that case the adapter and interface can be placed together:
class CreditCardPaymentServiceAdapter : IPaymentService
{
private CreditCardPaymentService service;
public CreditCardPaymentServiceAdapter(
CreditCardPaymentService service)
{
this.service = service;
}
// Implement IPaymentService here and forward
// to the CreditCardPaymentService.
}
This adapter itself will contain no business logic, but will just map/transform/adapt to the real CreditCardPaymentService and exposed the IPaymentService (or which interface is suited for that application).
If you have multiple applications, you might be forced to duplicate these adapters and the interface. That's the downside.
In a application that use Repositories and Services pattern, how to make sure Service layer is always called and not the Repositories directly ?
Example :
class OrderRepository
{
void CreateOrder(Order o)
...
}
class OrderService
{
void CreateOrder(Order o)
{
//make some business logic tests
...
//call repository
_orderRepository.CreateOrder(o);
}
}
I see two issues :
A programmer may call the repository directly because it doesn't know the existance of a service (sometimes its not as simple as in this example (1 service = 1 repository with same method names). some applications are not very well documented. or someone in hurry can forget to check if corresponding service exists (mistake)).
Totally different : long time ago someone created some views + controllers that use order repository directly. At that time there was no need to have some business logic check or additional operations, only order repository exists (because there it was not needed at all). If later, some additional operations when creating an order would be needed, a service will be created. the problem is that all controllers that make old repositories calls will need to be changed. Isn't repository principle/idea (and separating code in layers) supposed to make parts independent from each other ?
You can structure your solution so that all repositories and services are in their own respective projects, ex. Repositories and Services.
The only project that should reference Repositories would be Services. This way, other projects wouldn't have access to the repositories. Of course, nothing is to stop a developer from including the repositories project to the controllers project, but hopefully at this point they'll be asking themselves why it wasn't included in the first place.
Static analysis tools can help in this respect.
nDepend is a commercial tool that can be integrated into your build process and error on such a condition (any non service class calling a repository class directly).