So usually when implementing this pattern I have the Service take the Repository<Type> and then have the repository take the UnitOfWork.
I was playing around with hanging a method off the UnitOfWork that gets the Repository<Type> like so:
public class UnitOfWork : IUnitOfWork
{
public IRepository<TEntity> GetRepository<TEntity>() where TEntity : Core.Domain.Model.EntityBase<TEntity>
{
return new Repository<TEntity>(this);
}
}
Then the Service would take the UnitOfWork and could resolve the repositories needed from that.
What do you think? Do you see any flaws with this?
I use a similar approach in my ASP.NET MVC program and so far it is working very well.
My IUnitOfWork interface looks like this:
public interface IUnitOfWork
{
IRepository<TEntity> GetRepositoryFor<TEntity>() where TEntity : class;
void SaveChanges();
}
and the associated IRepository interface looks like this:
public interface IRepository<TEntity> : IQueryable<TEntity> where TEntity : class
{
TEntity Find(params object[] keyValues);
void Insert(TEntity entity);
void Update(TEntity entity);
void Delete(TEntity entity);
}
And then pass it to my service like so:
public abstract class BaseService
{
public BaseService(IUnitOfWork unitOfWork)
{
// etc...
}
}
You are right that this makes it easy for the service to resolve it's repositories without having to pass them into the constructor individually which is useful in cases where you might work with multiple repositories in a single service (E.G. Purchase orders and products).
One benefit of using ORM agnostic interfaces like this is that it means you can switch ORMs easily. I'll be honest, the chances of me changing from Entity Framework to another ORM is slim, but the fact is that I could if the need arises. As a bonus my services are much easier to test and I also find this makes my service class cleaner as it is now totally unaware of the ORM in use and is working entirely against the two interface above.
In regards to the comments about a generic repository interface, my advice is to be pragmatic and do what works best for you and your application. There is a number of questions on Stackoverflow on this very topic and the answers to them vary wildly about which is the best way to go (E.G. exposing IQueryable vs IEnumerable, Generic vs non-generic).
I toyed with not having a generic repository as you may already have noticed that my IRepository interface looks like IDbSet; The reason I went for this method is it allows my implementation to handle all of the Entity Framework entity state management stuff that you do with the DbContext E.G.
public void Delete(TEntity entity)
{
if (Context.Entry(entity).State == EntityState.Detached)
{
EntitySet.Attach(entity);
}
EntitySet.Remove(entity);
}
If I used IDbSet I would need to perform this in my service layer, which would then require a dependency on DbContext which seemed a much more leaky abstraction than my generic repository.
Related
I understand the basics of DI in .NET Core, but I'm having trouble figuring out how to use it with multiple projects. Imagine I'm setting up a database context in the Startup class of ASP.NET Core:
public void ConfigureServices(IServiceCollection services)
{
services.AddDbContext<GalleryDb>();
}
I know how to access that context in an API controller:
public class AlbumController : Microsoft.AspNetCore.Mvc.Controller
{
private GalleryDb _ctx;
public AlbumController(GalleryDb ctx)
{
_ctx = ctx;
}
}
But what does one do when there are many layers and functions between the API controller and the data access class? Eventually the code reaches my repository class, which is the one that actually requires the context. It looks like this:
public class AlbumRepository
{
private GalleryDb _ctx;
public AlbumRepository(GalleryDb ctx)
{
_ctx = ctx;
}
public void Save(AlbumEntity entity)
{
// Use _ctx to persist to DB.
}
}
I understand that I could pass the context from the API entry point all the way down, but that seems like an anti-pattern because it means passing it as a parameter through multiple classes and functions that have no interest in it.
Instead, I'd like to do something like this at the point where I invoke the repository class:
public void Save(AlbumEntity album)
{
var ctx = DependencyResolver.GetInstance<GalleryDb>();
var repo = new AlbumRepository(ctx);
repo.Save(album);
}
I believe some DI frameworks have something like this, but I'm trying to figure out how to do it with native .NET Core 2.0. Is this possible? What is the best practice? I found one thread (ASP.NET Core DependencyResolver) talk about using IServiceProvider but the implication was that this was not a desirable solution.
I'm hoping whatever the solution is, I can extend it to apply to other DI classes like ASP.NET Identity's RoleManager and SignInManager.
The key breakthrough chris-pratt helped me understand is that the only way this works is to use DI through all the layers. For example, down in the data layer I get a DB context through DI:
public class AlbumRepository
{
private GalleryDb _ctx;
public AlbumRepository(GalleryDb ctx)
{
_ctx = ctx;
}
}
In the business layer I use DI to get a reference to the data layer:
public class Album
{
private AlbumRepository _repo;
public Album(AlbumRepository repo)
{
_repo = repo;
}
}
Then, in the web layer, I use DI to get a reference to the business layer class:
[Route("api/[controller]")]
public class AlbumController : Microsoft.AspNetCore.Mvc.Controller
{
private Album _album;
public AlbumController (Album album)
{
_album = album;
}
}
By using DI through every layer, the DI system is able to construct all the necessary classes at the point where they are needed.
This requirement has a profound impact on the architecture of an application, and I now realize that my initial hope to tweak an existing, non-DI app to start using DI for the DB context is a major undertaking.
I understand that I could pass the context from the API entry point all the way down, but that seems like an anti-pattern because it means passing it as a parameter through multiple classes and functions that have no interest in it.
No, that's not an anti-pattern. That's how you should do it. However, the bit about "classes and functions that have no interest in it" makes no sense.
Simply, if you're working with something like a repository that wraps a DbContext (a horrible idea, by the way, but we'll put a pin in that), then you shouldn't ever be dealing directly with that DbContext. Instead, you should be injecting your repository into your controllers and then simply let the context be injected into that:
public void ConfigureServices(IServiceCollection services)
{
services.AddDbContext<GalleryDb>();
services.AddScoped<AlbumRepository>();
}
Since ASP.NET Core knows how to inject GalleryDb, and AlbumRepository takes GalleryDb as a constructor param, you simply register AlbumRepository for injection as well (using a "scoped" or request lifetime).
Now, you can inject AlbumRepository the same way you're currently injecting the context:
public class AlbumController : Microsoft.AspNetCore.Mvc.Controller
{
private AlbumRepository _repo;
public AlbumController(AlbumRepository repo)
{
_repo = repo;
}
}
Where this starts to get tricky is when you have many repositories, especially if you have controllers that need to interact with several repositories. Eventually, your code will become a rat's nest of service config and injection boilerplate. However, at that point, you should really be employing the unit of work pattern as well, encapsulating all your repositories in one class that you can inject instead. But wait, oh yeah, that's what DbContext is already. It's a unit of work encapsulating multiple repositories, or DbSets. This is why you shouldn't being using the repository pattern in conjunction with Entity Framework. It's a pointless abstraction that does nothing but add additional and unnecessary entropy to your code.
If you want to abstract DbContext, then you should use something like the service layer pattern (not to be confused with the RPC bull excrement Microsoft refers to as the "service pattern") or the CQRS (Command Query Responsibility Segregation) pattern. The repository pattern is for one thing: abstracting away raw SQL. If you don't have raw SQL, you should not be implementing that pattern.
I've implemented my UnitOfWork so that it keeps references to all repositories.
public interface IUnitOfWork
{
void Commit();
void RollBack();
}
public interface IMyUnitOfWork : IUnitOfWork
{
IFooRepository Foos { get; }
IBarRepository Bars { get; }
// Other repositories ...
}
Note that the repositories implements a generic type of repository interface.
public interface IFooRepository : IRepository<Entities.Foo>
{
// FooRepository specific methods goes here.
}
public interface IRepository<T> : IRepository
where T : class
{
}
Now how can I inject these repository to my UnitOfWork. Of course I want them with a lazy loading behavior. For example:
public class ConcreteUnitOfWork : IMyUnitOfWork
{
private readonly IUnityContainer unityContainer;
private IFooRepository fooRepository;
public ConcreteUnitOfWork(IUnityContainer unityContainer)
{
this.repositoryFactory = repositoryFactory;
}
public IFooRepository Foos
{
get
{
return this.fooRepository ??
(this.fooRepository = unityContainer.Resolve<IFooRepository>());
}
}
}
I know passing the Unity container to the UnitOfWork is incorrect but what pattern would you offer to solve this issue?
You may mention that I shouldn't keep the repository references in the UnitOfWork but please suppose a service class which needs several repositories. With this design I can just pass the UnitOfWork as the constructor parameter (Constructor Injection) to the service class, but if I didn't keep the repository references in UnitOfWork, I would have to pass all needed repositories as constructor parameters and you know what it leads to.
-- UPDATE --
Please let me know if I'm absolutely wrong and I should never compose the repositories in UnitOfWork. Then please give me a solution about "Constructor Over-injection" here.
-- UPDATE2 --
It seems that composing (referencing to) the repositories from UnitOfWork breaks the Open/Closed principle as we need to change the UnitOfWork class when we add a new repository (add a new property).
If it's right then I should consider a refactoring. Would you please give me some ideas?
It seems as though the current design proposal mixes more than one responsibility into the IMyUnitOfWork interface. You say that this is because otherwise a service class might need to take each Repository independently. I'm assuming you mean something like this:
public MyService(
IUnitOfWork uow,
IFooRepository fooRepository,
IBarRepository barRepository)
This seems to me to be a much simpler and cleaner design.
But then what about Constructor Over-injection?
Well, there's that... but the thing is that this is exactly the same problem you now have with your ConcreteUnitOfWork implementation. You haven't solved the Constructor Over-injection smell at all - you've just moved it to another class.
Actually, by moving it to ConcreteUnitOfWork you've made it more difficult to deal with the situation. Because ConcreteUnitOfWork is a pure infrastructure class (or a support class, if you will) it doesn't have any business context, so it's really hard to suggest a way resolve the Constructor Over-injection smell here.
On the other hand, a given Service (or perhaps a Controller) would tend to be more specialized and have knowledge of the business context, so it wouldn't need every repository in order to do its job - or if it does, it probably attempts to do too much.
Such a specific business component can better be refactored to a Facade Service.
I'm working on a large project using ASP.Net MVC 3, EF 4.1 and Ninject for Dependecy Injection. I've read through many of the existing questions here regarding DDD, EF and the Repository Pattern but I can't seem to find anyone incorporating stored procedures with these patterns.
I don't like the idea of implementing yet another repository pattern on top of what seems to already be a UnitOfWork/RepositoryPattern already defined with a DbContext. Also, I generally don't like the idea of creating Service and Repository classes for every type of entity in the system if possible.
The source of my problem stems from this common repository interface which everyone seems to use.
public interface IRepository<TEntity> where TEntity : class
{
TEntity Get(Expression<Func<TEntity, bool>> whereClause);
IEnumerable<TEntity> List();
IEnumerable<TEntity> Find(Expression<Func<TEntity, bool>> whereClause);
void Add(TEntity entity);
void Delete(TEntity entity);
// And so on...
}
That's great if all your queries can be in context of a single entity. Where this breaks for me is when I want to access a stored procedure. With EF 4.1 & Code Generatrion you can add stored procedures (e.g. SelectUser) and it will generate a context which looks something like this.
namespace MyCompany.Data.Database
{
using System;
using System.Data.Entity;
using System.Data.Entity.Infrastructure;
using System.Data.Objects;
using MyCompany.Domain.Entities;
using MyCompany.Domain.Contracts;
public partial class MyCompanyEntities : DbContext
{
public MyCompanyEntities()
: base("name=MyCompanyEntities")
{
this.Configuration.LazyLoadingEnabled = false;
this.Configuration.ProxyCreationEnabled = false;
}
protected override void OnModelCreating(DbModelBuilder modelBuilder)
{
throw new UnintentionalCodeFirstException();
}
public DbSet<Order> Orders { get; set; }
public DbSet<User> Users { get; set; }
public virtual ObjectResult<User> SelectUser(Nullable<int> userId)
{
((IObjectContextAdapter)this).ObjectContext.MetadataWorkspace.LoadFromAssembly(typeof(User).Assembly);
var userIdParameter = userId.HasValue ?
new ObjectParameter("UserId", userId) :
new ObjectParameter("UserId", typeof(int)); MyCompanyEntities x; x.
return ((IObjectContextAdapter)this).ObjectContext.ExecuteFunction<User>("SelectUser", userIdParameter);
}
public virtual ObjectResult<User> SelectUser(Nullable<int> userId, MergeOption mergeOption)
{
((IObjectContextAdapter)this).ObjectContext.MetadataWorkspace.LoadFromAssembly(typeof(User).Assembly);
var userIdParameter = userId.HasValue ?
new ObjectParameter("UserId", userId) :
new ObjectParameter("UserId", typeof(int));
return ((IObjectContextAdapter)this).ObjectContext.ExecuteFunction<User>("SelectUser", mergeOption, userIdParameter);
}
}
}
As part of my DDD setup I have a UserService class and I would like to 'inject' a repository to its constructor. Many examples suggest that the constructor should accept an (IRepository<User> userRepository). This doesn't work for me. Stored procedures are generated on the DbContext class as a method and I am unable to see it.
The only thing I can think of is to either create another interface with the stored procedure methods on it. I don't really want to add it to the generic IRepository because then when you have an instance of IRepository<Order> you'll still see SelectUser which seems a bit odd. Maybe it's not a big deal?
Perhaps I'm going about this the wrong way. Should I not be bothering with creating an interface on top of my DbContext if I'm not trying to create a whole new repository pattern? I was really creating it for the dependency injection. Would it be wrong if the UserService constructor took a MyCompanyEntities instance instead of an interface?
What you found is natural. The problem is that generic repository is insufficient for real scenarios. It is only good for "base" implementation. You need specific repository for User entity which will expose method wrapping call to context exposed stored procedure.
Hi looking at the repository pattern which commonly seems to be implemented something like:
public class GenericRepository<TEntity> where TEntity : class
{
// other business
public virtual TEntity GetByID(object id)
{
return db.Set().Find(id);
}
public virtual void Insert(TEntity entity)
{
db.Set().Add(entity);
}
public virtual void Delete(object id)
{
TEntity entityToDelete = db.Set().Find(id);
Delete(entityToDelete);
}
public virtual void Update(TEntity entityToUpdate)
{
db.Set().Attach(entityToUpdate);
context.Entry(entityToUpdate).State = EntityState.Modified;
}
}
So for every type you want to work with (ie update) you need to instantiate a repository.
So if I had two types I wanted to save Cars and Trucks I would need to go:
var carRepository = new GernericRepository<Car>();
carRepository.Update(myCar);
var truckRepository = new GernericRepository<Truck>();
carRepository.Update(myTruck);
So then you have seperate repositories for each type. To make sure you save everything at once you need the unitOfWork to ensure they all use the same context and save at one time.
Surely wouldn't it be better to have something like:
public class GenericRepository
{
// other business
public virtual TEntity GetByID<TEntity>(object id) where TEntity : class
{
return db.Set<TEntity>().Find(id);
}
public virtual void Insert<TEntity>(TEntity entity) where TEntity : class
{
db.Set<TEntity>().Add(entity);
}
public virtual void Delete<TEntity>(object id) where TEntity : class
{
TEntity entityToDelete = db.Set<TEntity>().Find(id);
Delete(entityToDelete);
}
public virtual void Update<TEntity>(TEntity entityToUpdate) where TEntity : class
{
db.Set<TEntity>().Attach(entityToUpdate);
context.Entry(entityToUpdate).State = EntityState.Modified;
}
}
This means the repository only needs to be instantiated once and therefore is truely generic?
So you could update your cars and trucks like this:
var repository = new GernericRepository<Car>();
repository.Update<Car>(myCar);
rRepository.Update<Truck>(myTruck);
Surely this is a better method? Am I missing something? It automatically has only one context too.
The repository pattern does not decouple the data access from the data store, that is what the ETL tool such as NHibernate or the Enity Framework does for. The repository pattern provides reusable methods for extracting data.
I have previously used a so called "Generic" repository as you have described and thought it was great. It isn't until you realise that you have just put another layer on top of NHibernate or the Entity Framework you realise it's all gone Pete Tong.
Ideally what you want are interfaces that describe ways of getting data out of your data store and should not leak what data access you are using. For example:
public interface IEmployee
{
IEmployee GetEmployeeById(Guid employeeId);
IEmployee GetEmployeeByEmployeeNumber(string employeeNumber);
IEnumerable<IEmployee> GetAllEmployeesWithSurname(string surname);
IEnumerable<IEmployee> GetAllEmployeesWithStartDateBetween(DateTime beginDateTime, DateTime endDateTime);
}
This gives you a contract to code to, there is no knowledge of your persistence layer and the queries used to retrieve the data can be unit tested in isolation. The interface could inherit from a base interface that provides common CRUD methods but you would be assuming that all your repositories would need CRUD.
If you go down the road of a Generic Repository you will end up with duplication in your queries and you will find it much harder to unit test the code that uses the repository as you will have to test the queries as well.
Generics by itself does not make an implementation of the repository pattern. We've all seen the generic base class used in example repository pattern implementations but this is to make things DRY (Don't-Repeat-Yourself) by inheriting from the base class ( GenericRepository in your case) to more specialized child classes.
Only using the generic, base class GenericRepository assumes that your repositories will only ever need the most basic CRUD methods. For a more complex system, each repository becomes more specialized based on underlying business entities data requirements.
Also, you will need to have interfaces that define your data contracts with your other layers. Using the repository pattern means you don't want to expose your concrete implementations of your repositories to your other layers.
I am currently using the ASP.NET MVC framework on a project (pretty much my first time)
I am using Linq2SQL as my data model..
Where should i have this kind of code:
var entries = from e in db.sometable select e;
I currently have this kinda code in the controller and pass the data i get into the view..
is this ok?
if not how do i entend my linq2sql datamodel to include this kindof code?
Thanks
Daniel
To add what #Poco said, here's an example:
In Foo.Common.Repositories (inside the Foo.Common Project):
public interface IRepository<T>
{
IEnumerable<T> GetAll();
void Update(T entity);
void Add(T entity);
void Delete(T entity);
void Save();
}
public interface IUserRepository : IRepository<User>
{
void GetByCredentials(string username, string password);
}
The inside Foo.Data.Repositories (inside Foo.Data project):
public class UserRepository
{
// ... other methods/properties snipped.
public IEnumerable<User> GetAll()
{
// Where this.Users would be L2Sql or Code-First... or some other ORM.
return from u in this.Users orderby u.Name select u;
}
}
Then inside your actual Foo.Web:
public class UserController : Controller
{
private readonly IUserRepository userRepository;
public UserController(IUserRepository userRepository)
{
this.userRepository = userRepository;
}
[AcceptVerbs(HttpVerbs.Get)]
public ViewResult List()
{
var users = this.userRepository.GetAll();
return this.View(users);
}
}
And inside your Global.asax you'd have Ninject or some other IoC container to resolve IUserRepository:
public static void RegisterServices(IKernel kernel)
{
kernel.Bind<IUserRepository>().To<UserRepository>();
}
protected void Application_Start()
{
var kernel = new StandardKernel();
AreaRegistration.RegisterAllAreas();
MvcApplication.RegisterGlobalFilters(GlobalFilters.Filters);
MvcApplication.RegisterRoutes(RouteTable.Routes);
MvcApplication.RegisterServices(kernel);
// I'm using MVC3 here:
DependencyResolver.SetResolver(new NinjectResolver(kernel));
}
It's common to use the Repository pattern for MVC.
Typically, you define an interface, for instance, IProducts, and then, you implement this interface, calling you linq2sql code. Your controller will accept this interface as a parameter for the constructor, so that it depends on this interface, and not on a concrete class. Using a dependency injector, such as Ninject, will allow you to supply a concrete interface implementation to the constructor. This enables Unit Testing on you web app, and also adds flexibility.
There's a really nice book, Pro ASP.NET MVC 2 Framework, that explains all that. I'm currently reading it, and I just love it.
Here's an example of how to implement the repository pattern
In addition to this I would implement an additional layer to handle your applications business logic and keep your controllers lightweight
It's fine to have Linq queries in controller methods.
If we're talking about separation of concerns, the idea is that your data layer (in this case, the repository(?) code that supplies you with db.sometable) decouples your logic code (controller methods in this case) from the datastore.
You query the data layer rather than the database, so you can change the underlying datastore and your controller code will still work.
Some would argue that it's better again to move as much logic code as you can out of the controllers and into your model code (see the first answer here), but it depends how far you want to go.