I'm currently working on a web app which consist of 6 layers:
Web (reference to ViewModels and Controllers)
ViewModels
Controllers
Services (reference to Data and Entities)
Data (reference to Entities)
Entities
What I'm trying to is to implement a "UnitOfWork" pattern, and therefore I have a class thats injected by DI for that job which makes it possible to do .commit() in the actionresult in the controller when I'm done with the database.
Now is my question... Where should this UnitOfWork class be placed? It's at the moment in my Data layer but that requires the Controller layer to reference the Data layer AND the Service layer, which is odd in my opinion... Should I move the UnitOfWork class/interface to the Service layer and use DI?
Unless you're using the Repository pattern in your Data layer, you're wasting your time.
The point of a UoW is to handle changes across multiple Repository instances, this is done in the following ways:
Unit of Work derives from the actual underlying context (DataContext - L2SQL, ObjectContext/EF)
Repositories take a Unit of Work in their ctor.
The Unit of Work do two things:
Have a Commit() method
Expose the underlying object/entity set to the Repository.
It's a little tricky to get it all setup, but once you do, the flow should be like this:
Controller get's DI'ed a service and a unit of work (both via Interfaces)
Controller calls method on a service ("CustomerServices.AddOrder()")
Service calls method on Repository
Repository calls "Add" method on "Order" object/entity set
Controller commits Unit of Work
Essentially, each layer takes an instance of the "next layer" in their constructor. Everything should be DI'ed and interface-driven. The UoW has not reliance on anything - but the Repository relies on it for persistence to the "internal memory" (ORM), then the UoW "Commit" will push the changes out to the database (basically wraps the "SaveChanges" method).
As the Unit of Work is an infrastructure/persistence/database/transactional concern, it should go into your Data layer. Should only be referenced by Controllers.
I implemented my IUnitOfWork class to be passed directly into my MVC controllers (injected via Castle Windsor). I then have my controller pass it to any service objects it instantiates.
IUnitOfWork should be an interface for data layer. When request come into Controller then call service methods, if you require CRUD there should call UnitOfWork. You may use Session Per Request by call UnitOfWork in Global.asax Request_Start and commit works in Request_End.
Related
Inside the project I work on (ASP.NET Core with EF), I have implemented Repository Pattern with UnitOfWork, and in my UnitOfWork class I have the SaveChanges() method.
Now I must add a new layer of services which will contain the app logic and the calls to the repository classes. All the things were good until I reached the SaveChanges() method.
I don't want to call UnitOfWork.SaveChanges() at the end of every method from my service classes. Another thing that I want to avoid is to call the SaveChanges() when all the modifications are done, lets say EmployeeService.SaveChanges(), but the changes are made by multiple services, eg: ShopService, ClientService and EmployeeService. To call the EmployeeService.SaveChanges() for me it seems contra intuitive because the changes that should be saved are also related to ShopService and ClientService, not just with the service class from where the save method is called.
In order to make a summary of my problem, I could say that I'm asking for a solution to save the changes at the service layer level when I have multiple changes made by multiple services. I want to save them just once at the end.
UnitOfWork should call BeginTransaction/CommitTransaction. Each Service can then call SaveChanges as necessary. For instance, a Service may need to add an entity and use its database-generated ID, which requires immediately calling SaveChanges.
I want to know whether I can use object of service layer marked with #Service annotation and call one of its method in non mvc-spring class ?
Say there is a method getUsers() in service layer which calls getUsers() of Dao layer. In order to use it in contoller I have to add the #Autowired-annotation in the service layer instance. But if I want to use the class method getUsers() in non-mvc class, how can I do that?
In order to use a service, that object must be container managed. That is, this object's life cycle must be managed by Spring (creation, destruction, initialisation,...).
So to inject an instance of your service in an object, it must be a Spring bean too (Service, Component, Controller...).
So, it may be an MVC object, but it doesn't have to.
On the other hand, there is another alternative: use the annotation #Configurable.
An object with this annotation can be application managed but Spring, using byte code aspects, can inject it's dependencies. So although you create the object with a new statement, Spring instruments this call and resolve all the annotated dependencies.
Read this for more detail:
http://docs.spring.io/spring/docs/3.0.0.M3/spring-framework-reference/html/ch08s08.html
I have started to go through Symfony2 code, studied a little bit small classes like Pimple and after few hours of examination have come to strange idea. The best start for this is to explain how I understand few terms, so:
Dependency
Something which is needed for another thing to work, like "engine" in "car"
Container
Object or class which is able to store a lot of another objects, like "engine","gearbox" or even "car"
Dependency Injection
Process in which every dependency is injected to object, so if I need "car" I know that I have to inject "engine","gearbox" and a lot of another stuff. Important is, that "car" don't create "engine", but "engine" is put inside "car"
Service Locator
Process in which object asks for another object, for example into the car there is inserted our container, and when car need to start it require from container "engine", so container return him "engine"
When i studied Symphony code, they start with dependency injection, but after some time I realize that when Controller is created, there is injected whole container and then you can use $this->get('serviceName') to get it, so it more looks like service locator, which according to few articles is anti-pattern.
Sow how is it? Is that line between DI and SL so small that it is sometimes broken? Or did I misunderstood something? If I use DI, do I need to insert every service into controller, so I know from outside what I use? Or can controller become in some cases container?
Your understanding of DI is pretty good. And yes, Symfony Controller does implement ContainerAwareInterface, and as you said, has a service locator role. But service locator isn't an anti-pattern. Each pattern has it's proper and improper uses.
Furthermore, Symfony doesn't enforce you in any way to use it's Controller. Your Controller can be a service. Hell, it can even be a function!
Here is one of the reasons why Controllers are implemented as service locators: Performance.
Let's drop car analogy and focus on real case that you'll encounter in 99% of projects: you need CRUD for a resource. Let's say you're building a Todo app and you need a RESTfulish controller to handle CRUD operations for Task Resource.
The least you need to have is a way to read all tasks and a way to add a new task, for that you need two actions: index (commonly named list too), and store (commonly named create too).
Common flow in Symfony would be this, in pseudo code:
indexAction -> getDoctrine -> getTaskRepository -> getAllTasks
storeAction -> getFormFactory -> createForm -> bindRequestDataToForm -> getDoctrine -> saveData
If Controller was a service locator
Index Action
When index action is executed, only service that will be resolved from the container will be ManagerRegistry (in this case Doctrine service). We will then ask it to give us task repository, and we'll do our operation with it.
Store Action
When store action is executed, we will do a bit more work: ask container to give us FormFactory, do some operations with it, and then ask it to give us Doctrine and do some operations with it too.
So summary: when index action is executed, only one service has to be constructed by service container, when update is executed, two will have to be constructed.
If Controller was a regular service
Let's see what our Controller needs. From the section above, we see that it needs FormFactory and Doctrine.
Now, when you just want to call index action to read all tasks from data storage, your controller will have to get instantiated by container. Before it can be instantiated, container needs to instantiate it's dependencies: FormFactory and Doctrine. Then instantiate controller while injecting those two into it.
So, you are calling index action which doesn't need FormFactory at all, but you still have overhead of creating it because it is needed for an action that will not be called at all in that request.
Lazy Services
To reduce this overhead, there is a thing called lazy service. It works by actually injecting a Proxy of your service into the controller. So, as far as controller is concerned, it got FormFactory. What it doesn't know is that isn't real FormFactory but instead a fake object which will delegate calls to real FormFactory code when you call some method on it.
Wrapping it up
Controller doesn't have to be a service locator, but can be. Making it a service locator can be a bit more performant and easier to bootstrap, but hides dependencies. Furthermore, it's a bit harder to test, since you'll need to mock dependency container. Whether you want to make your controllers services, functions or service locators is your choice and Symfony won't enforce you to use any of those ways.
In my experience, extending default Symfony Controller and having controllers be service locators is just fine as long as you don't write your business logic in them, but instead delegate all that work to services, which you get from container. That way, it's really unlikely that you'll have bugs in controller code (as methods will usually consist of 2-3 lines of code) and can get away without testing it.
My application is using SQL Server 2012, EF6, MVC and Web API.
It's also using a repository and assorted files such as:
DatabaseFactory.cs
Disposable.cs
IDatabaseFactory.cs
IRepository.cs
IUnitOfWork.cs
RepositoryBase.cs
UnitOfWork.cs
We already use a service layer between our controllers and the repository
for some complicated business logic. We have no plans EVER to change to a different database and it has been pointed
out to me that the recent thinking is that EF6 is a repository so why build
another repository on top of it and why have all of the files I have above.
I am starting to think this is a sensible approach.
Does anyone know of any examples out there that implement EF6 without a
repository, with a service layer. My search on the web has revealed many
complex code examples that seem over complicated for no reason at all.
My problem is also when using a Service Layer then where do I put:
context = new EFDbContext()
In the controller, the service layer or both ? I read that I can do this with dependancy injection. I already use Unity as an IOC but I don't know how I can do this.
Entity Framework IS already a Unit of Work pattern implementation as well as a generic repository implementation (DbContext is the UoW and DbSet is the Generic Repository). And I agree that it's way overkill in most apps to engineer another UoW or Generic Repository on top of them (besides, GenericRepsitory is considered to be an anti-pattern by some).
A Service layer can act as a concrete repository, which has a lot of benefits of encapsulating data logic that is specific to your business needs. If using this, then there is little need to build a repository on top of it (unless you want to be able to change your backend service technology, say from WCF to WebApi or whatever..)
I would put all your data access in your service layer. Don't do data access in your controller. That's leaking your data layer into your UI layer, and that's just poor design. It violates many of the core SOLID concepts.
But you do NOT need an additional UnitOfWork, or other layers beyond that in most cases, unless your apps are very complex and intended to work in multiple environments...
Setting up Unity for ASP.NET MVC and WebAPI is quite easy if you install and add the Unity.Mvc* and Unity.WebAPI* Nuget packages to your project. (The * is a version number, like 3 or 4 or 5. Look for the appropriate versions for your project. Here are for example the links to the Unity.Mvc 5 package and to the Untity.WebAPI 5 package.)
The usage of these packages is explained in this blog post.
The building blocks are roughly like so:
You build a unity container and register all your dependencies there, especially the EF context:
private static IUnityContainer BuildContainer()
{
var container = new UnityContainer();
container.RegisterType<MyContext>(new HierarchicalLifetimeManager());
container.RegisterType<IOrderService, OrderService>();
container.RegisterType<ICustomerService, CustomerService>();
container.RegisterType<IEmailMessenger, EmailMessenger>();
// etc., etc.
return container;
}
MyContext is your derived DbContext class. Registering the context with the HierarchicalLifetimeManager is very important because it will ensure that a new context per web request will be instantiated and disposed by the container at the end of each request.
If you don't have interfaces for your services but just concrete classes you can remove the lines above that register the interfaces. If a service needs to be injected into a controller Unity will just create an instance of your concrete service class.
Once you have built the container you can register it as dependency resolver for MVC and WebAPI in Application_Start in global.asax:
protected void Application_Start()
{
var container = ...BuildContainer();
// MVC
DependencyResolver.SetResolver(
new Unity.MvcX.UnityDependencyResolver(container));
// WebAPI
GlobalConfiguration.Configuration.DependencyResolver =
new Unity.WebApiX.UnityDependencyResolver(container);
}
Once the DependencyResolvers are set the framework is able to instantiate controllers that take parameters in their constructor if the parameters can be resolved with the registered types. For example, you can create a CustomerController now that gets a CustomerService and an EmailMessenger injected:
public class CustomerController : Controller
{
private readonly ICustomerService _customerService;
private readonly IEmailMessenger _emailMessenger;
public CustomerController(
ICustomerService customerService,
IEmailMessenger emailMessenger)
{
_customerService = customerService;
_emailMessenger = emailMessenger;
}
// now you can interact with _customerService and _emailMessenger
// in your controller actions
}
The same applies to derived ApiControllers for WebAPI.
The services can take a dependency on the context instance to interact with Entity Framework, like so:
public class CustomerService // : ICustomerService
{
private readonly MyContext _myContext;
public CustomerService(MyContext myContext)
{
_myContext = myContext;
}
// now you can interact with _myContext in your service methods
}
When the MVC/WebAPI framework instantiates a controller it will inject the registered service instances and resolve their own dependencies as well, i.e. inject the registered context into the service constructor. All services you will inject into the controllers will receive the same context instance during a single request.
With this setup you usually don't need a context = new MyContext() nor a context.Dispose() as the IOC container will manage the context lifetime.
If you aren't using a repository then I assume you would have some place to write your logic/processing that your service operation would use. I would create a new instance of the Context in that logic/process class method and use its methods directly. Finally, dispose it off right after its use probably under a "using".
The processing method would eventually transform the returned/processed data into a data/message contract which the service returns to the controller.
Keep the data logic completely separate from Controller. Also keep the view model separate from data contract.
If you move ahead with this architecture, you are going to be tightly coupling the Entity Framework with either your service or your controller. The repository abstraction gives you a couple things:
1) You are able to easily swap out data access technologies in the future
2) You are able to mock out your data store, allowing you to easily unit test your data access code
You are wondering where to put your EF context. One of the benefits of using the Entity Framework is that all operations on it are enrolled into a transaction. You need to ensure that any data access code uses the same context to enjoy this benefit.
The design pattern that solves that problem is the Unit of Work pattern, which by the looks of things, you are already using. I strongly recommend continuing to use it. Otherwise, you will need to initialize your context in your controller, pass it to your service, which will need to pass it to any other service it interacts with.
Looking at the objects you have listed, it appears to be a considerate attempt to build this app with enterprise architectural best practices. While abstractions do introduce complexity, there is no doubting the benefit they provide.
I am redesigning a solution's architecture to implement SOA.
After doing the design changes I have come up with:
MySolution.Client.MyProject.Web ...... //ASP.NET WebSite
MySolution.Client.MyProject.Proxy .... //Service Proxy C# Library Project *1
MySolution.Service ................... //Service.cs for Service.svc is here
MySolution.Service.DataContract ...... //IService.cs for Service.cs is here *[2]
MySolution.Service.HttpHost .......... //Service.svc is here
MySolution.Model ..................... //All custom data classes and EDMX model is here *[3]
MySolution.Repository ................ //Repository queries the DB using LINQ and ADO.NET queries
*1 MySolution.Client.MyProject.Proxy:
This project contains service proxy and contains presentation classes
*[2]MySolution.Service.DataContract:
This project contains IService and Request/Response Classes
All methods in Service.cs takes the Request classes as input and return Response classes as output
Therefore this project is referenced by the 2 Client Projects(Web and Proxy), as it contains the IService and all of the Request/Response classes that will be required to communicate with Service.cs
*[3]MySolution.Model:
This project contains the .edmx that is the Data Model of Entity Framework and some custom classes that are used in the project.
PROBLEM:
Because I only use request/response classes to communicate between service and client, the MySolution.Service.DataContract project is only used by Service.cs and Repository.cs
And due to that all responses that Repository generates I have to map them to the properties of its respective response class (which make both the original returned entity, and the response class almost identical). But I am OKAY with it...
For example:
The GetCustomer() in Repository.cs method is called by Service.cs
The GetCustomer() method in repository performs the LINQ query and returns a "Customer" object
Service.cs then maps all the properties of "Customer" object to the "CustomerResponse" object
Service.cs then returns the "CustomerResponse" to the caller.
In this case, most of the properties will repeat in both classes. If there is a solution to this, it's good, otherwise, I am fine with it.
However, when Repository.cs's method GetCustomers() (Notice it's not GetCustomer()) is called, it will return a list of Customer objects, and mapping this for return purposes would mean a "for loop" that iterates the collection and do the mapping... This is NOT OKAY...
Is there a better way of doing this, considering I do not want to return "Customer" object without "CustomerResponse" as first of all it violates the SOA architecture, and secondly I don't want my client projects to have any reference to the Model or Repository projects?
So is it just the mapping that you're having trouble with? If so, you could look at some open source mapping libraries like Mapper Extensions or AutoMapper that will automate the task.
If you don't like separate mapping between entities and DTOs expose IQueryable in your repository and use direct projections to DTOs. The disadvantage is that such solution can't be effectively unit tested. Mocking repository in such scenario doesn't make sense because query agains mock is Linq-to-objects whereas query against real repository is Linq-to-entities (different set of features where difference can be seen only at runtime).
Btw. I don't see too much SOA in your application - I see just multi tier application. It is like planting a tree in a garden and saying that you have a forest. Moreover it sounds like you are building CRUD interface (entities almost 1:1 to DTOs). I have a bad feeling that you are investing too big effort to architecture which you don't need. If your main intention is to build CRUD operations exposed as services on top of database you can expose entities directly moreover you can use tools like WCF Data services.
It sounds like your main point of grief is the tedious mapping of data objects to data transfer objects (DTOs). I haven't used this myself, but it seems like AutoMapper is made for doing automatic object-to-object mappings declaratively.
I would definitely stick to having your data objects separate from the data contracts in your services.