I want to use DI to manually inject an IDBConnection in my api controllers. I know I can put it in the constructor:
public MyController(IDBConnection cnn) { this._Connection = cnn; }
Or I could use the [FromServices] attribute:
[FromServices]
public IDbConnection _Connection { get; set; }
And I can use it in views like this:
#inject IDbConnection cnn
What I would really like to do would be to have it in a using, and have the DI open the connection so I could do something like this:
using (var cnn = Services.Inject<IDbConnection>()) {
// do something, don't worry about opening or closing
}
I'm declaring it like this:
services.AddTransient<IDbConnection>(x =>
{
string connectionString = Configuration.Get<string>(
"Data:DefaultConnection:ConnectionString");
return new SqlConnection(connectionString);
});
Should I create a class inheriting from SqlConnection that calls Open() in it's constructor? How can I access Configuration from there? I could create it like that to inject configuration or the connect string... Is using not required? Is there basically no overhead with just creating the instance so it wouldn't matter if some actions needed multiple connections to different databases?
I recommend that you create a service layer that your controller will depend on instead of directly accessing the db connection (and you won't have to this in your views #inject IDbConnection cnn). Your views should only declare the Model that your controller method returns and you will have nice intellisense support in the view pages.
public class ProductServices(){
public ProductServices(IDbConnection conn){
...
}
public List<Product> GetProducts(){
...
}
}
using is not required. As a rule of thumb, if the instance is created via IoC container (eg. Unity, Autofac, Ninject, etc), it should also be destroyed by the IoC container.
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 am making a website using ASP.NET MVC and an onion architecture. I have the following architecture:
Domain : Entities / Domain Interfaces
Repository : Generic repository (for now) using Entity Framework Code First Approach
Service : Generic Service that calls the Repository
MVC
Now I am trying to create a method in my controller to start testing the methods I have implemented in Repository and Service, and I am having a hard time as to what I am allowed to create in this controller. I want to test a simple Get method in the Repository, but to do that I need GenericService object and GenericRepository object in my controller. To demonstrate what I mean here's a snippet of my GenericRepository(I will skip the interfaces):
public class GenericRepository<T> : IGenericRepository<T> where T : class
{
private readonly PrincipalServerContext context;
private DbSet<T> entities;
public Repository(PrincipalServerContext context)
{
this.context = context;
entities = context.Set<T>();
}
}
Now my GenericService:
public class GenericService<T> : IGenericService<T> where T : class
{
private IRepository<T> repository;
public GenericService(IRepository<T> repository)
{
this.repository = repository;
}
public T GetEntity(long id)
{
return repository.Get(id);
}
}
And finally, my question, am I allowed to create these objects in my controller as follows (using my dbcontext called PrincipalServerContext):
public class NavigationController : Controller
{
private IGenericService<DomainModelClassHere> domainService;
private IGenericRepository<DomainModelClassHere> domainRepo;
private PrincipalServerContext context;
public ActionResult MyMethod(){
context = new PrincipalServerContext();
domainRepo = new GenericRepository<DomainModelClassHere>(context);
domainService = new GenericService<DomainModelClassHere>(domainRepo);
if(domainService.GetEntity(1)==null)
return View("UserNotFound");//Just as an example
return View();
}
}
Is this allowed? According to Jeffrey Palermo, UI can depend on Service and Domain so I don't know about the Repository. Technically I am not using methods from repository, but I do need to add a reference to the project.
If I can't then how can I create a new GenericService if I don't have a GenericRepository? Is there a better way to instantiate my objects ?
EDIT I think the answer to my question resides in Startup.cs where I can put something like service.addScoped(typeof(IGenericRepository<>),typeof(GenericRepository<>));
but I 'm not sure about this, any ideas?
I'll answer this on my own if ever someone encounters the same problem. There are configuration methods we can use to create instances of classes when needed. In the Startup.cs file you have to add ConfigureServices(IServiceCollection services) method and inside there are several methods that can be applied to services to create these instances. For example you can use:
services.AddTransient(IGenericRepository, GenericRepository)
What is the difference between services.AddTransient, service.AddScope and service.AddSingleton methods in Asp.Net Core 1? (this link explains differences between methods).
AddTransient is good in my case because it creates an instance of an object through the whole lifespan of the application, which is what I need. This means UI is dependant on the rest of the solution, because Startup.cs needs to know about the Repositories as well as the Services.
A pretty good answer can be found here :Onion Architecture : Can UI depend on Domain.
I have an MVC application using Ninject to connect to a single database. Now I need to support multiple databases. Currently, my global.asax.cs file has the following definition for ninject:
protected void Application_Start()
{
AreaRegistration.RegisterAllAreas();
RegisterRoutes(RouteTable.Routes);
//Using DI for controllers - use the Ninject custom controller factor
ControllerBuilder.Current.SetControllerFactory(new NinjectControllerFactory()); // Repository config is defined in ninject controller
}
And here is what my Ninject controller class looks like:
public class NinjectControllerFactory : DefaultControllerFactory
{
private IKernel kernel = new StandardKernel(new EriskServices());
protected override IController GetControllerInstance(RequestContext context, Type controllerType)
{
if (controllerType == null)
return null;
return (IController)kernel.Get(controllerType);
}
private class EriskServices : NinjectModule
{
public override void Load()
{
Bind<IRisksRepository>().To<MySql_RisksRepository>()
.WithConstructorArgument("connectionString", ConfigurationManager.ConnectionStrings["mydb1"].ConnectionString);
}
}
}
I also have a login page that handles user authentication. It is done through LDAP and does not require database connection.
My question is: Can I bind the ninject connectionString after the user authentication login page? The user would have a dropdown list for database they want to connect to, for example "mydb1" or "mydb2" or "mydb3". Each connection string would be defined in the web.config file.
Please help! Thank you!
No, you can't bind "after" - for one thing, web applications are stateless and you have no control over the order of events, but more importantly, Ninject modules define your IoC container and this configuration happens before almost anything else in the application or request lifecycle.
If you're saying that the user would pick this from a drop-down, then the act of choosing the repository is part of your application logic, not part of your IoC configuration. The way to deal with this is to create a factory interface. The implementation can be a thin wrapper around the Ninject kernel itself.
public interface IRisksRepositoryFactory()
{
IRisksRepository GetRepository(string name);
// Optional: add a GetRepositoryNames() method for populating dropdowns, etc.
}
public class NinjectRisksRepositoryFactory
{
private readonly IKernel kernel;
public NinjectRisksRepositoryFactory(IKernel kernel)
{
if (kernel == null)
throw new ArgumentNullException("kernel");
this.kernel = kernel;
}
public IRisksRepository GetRepository(string name)
{
return kernel.Get<IRisksRepository>(name);
}
}
For this particular implementation you'd want to make sure you use named bindings (although generally speaking you could also use the metadata system), and do each binding explicitly:
Bind<IRisksRepository>()
.To<MySqlRisksRepository>()
.InRequestScope()
.Named("mysql")
.WithConstructorArgument("connectionString", GetConnectionString("mydb1"));
Bind<IRisksRepository>()
.To<OracleRisksRepository>()
.InRequestScope()
.Named("oracle")
.WithConstructorArgument("connectionString", GetConnectionString("ordb1"));
Bind<IRisksRepositoryFactory>()
.To<NinjectRisksRepositoryFactory>();
It's also possible to do this without creating each binding explicitly, particularly if all targets are the same type (i.e. you only have a MySqlRisksRepository), by passing the connection string or related symbol as a parameter to the Get call and binding to a contextual method instead of a type - but I'd recommend against it, since it's really swimming against the current as far as DI in general goes.
One more thing: Don't worry that this resembles the "service locator" anti-pattern, because that's all it is - a superficial resemblance. When objects need to be able to create dependencies on the fly, creating special-purpose factories around the IoC container is the recommended solution, as it minimizes kernel exposure to a single class which could be easily replaced if you switched to a different framework.
What is the best way to manage the context of Entity Framework when using MVC application?
I am using a Repository/Service pattern.
Edit
After looking through some of these questions: stackoverflow.com/users/587920/sam-striano, I am more confused then before. Some say use the context per repository, but wht if I want to use multiple repositories in one controller method?
And to follow good separation design, how do you use UnitOfWork in the MVC app with out making it dependent on EF? I want to be able to unit test my controllers, model, services, etc. using a mock context?
Use a Dependency Injector/Inversion of Control framework like:
Ninject
Autofac
StructureMap
Unity
Using an IoC container, you can tell it how to manage a single data context (most commonly, per request). When you set the data context to per request, the container will auto-magically give any class that needs a data context the same data context per request.
Here is a good article on setting up Ninject.
What your code will most likely end up looking like, assuming you're using a generic repository:
Ninject Module:
public class NinjectRegistrationModule : NinjectModule
{
public override void Load()
{
Bind<MyDataContext>().ToSelf().InRequestScope();
Bind(typeof(RepositoryImplementation<>)).ToSelf().InRequestScope();
}
}
Generic Repository:
public RepositoryImplementation<T> : IRepository<T> where T : class
{
MyDataContext _dataContext;
public RepositoryImplementation<T>(MyDataContext dataContext)
{
_dataContext = dataContext;
}
// bunch of methods that utilize _dataContext
}
Service Class:
public class MyServiceClass
{
IRepository<SomeEntity> _someEntityRepository;
public MyServiceClass(IRepository<SomeEntity> someEntityRepository)
{
_someEntityRepository = someEntityRepository;
}
// do stuff with _someEntityRepository = someEntityRepository;
}
Controller:
public class MyController
{
MyServiceClass _myServiceClass;
public MyController(MyServiceClass myServiceClass)
{
// Ninject will auto-magically give us a myServiceClass
// which will Ninject will inject a repository into MyServiceClass's constructor
_myServiceClass = myServiceClass;
}
public ActionResult MyAction()
{
// use _myServiceClass to do stuff
return View();
}
}
If your functionality is straight forward, then you should create a new ObjectContext in each Repository. They are cheap to instantiate.
If this creates a conflict, you can use a Unit of Work pattern as was suggested in the comment.
I would advise that you be extremely cautious when integrating an ObjectContext or DataContext with a DI container. Many do not use the appropriate scope for their life cycle by default.
here's the default AccountController.cs that's generated by the framework.
public class AccountController : Controller
{
public IFormsAuthentication FormsAuth { get; private set; }
public IMembershipService MembershipService { get; private set; }
public AccountController()
: this(null, null)
{
}
public AccountController(IFormsAuthentication formsAuth, IMembershipService membershipService)
{
FormsAuth = formsAuth ?? new FormsAuthenticationService();
MembershipService = membershipService ?? new AccountMembershipService();
//---
}
This is easy to understand.
public AccountController(IFormsAuthentication formsAuth,
IMembershipService membershipService)
{
FormsAuth = formsAuth ?? new FormsAuthenticationService();
MembershipService = membershipService ?? new AccountMembershipService();
}
What's this? What's its purpose? Is it particular to the Account Controller or is it a requirement for other controllers? and, why should I incorporate it in my project?
public AccountController()
: this(null, null)
{
}
They seem to use this type of constructors in two other places.
Thanks for helping
This is actually an implemenation of the Bastard Injection anti-pattern.
The idea is that Constructor Injection is supported to allow Dependency Injection (DI), while still providing a default constructor for default behavior.
It's really not necessary to have the default constructor, but if you omit it, you must supply a custom IControllerFactory, as the DefaultControllerFactory assumes that all Controllers have default constructors.
ASP.NET MVC is built with DI in mind, but I guess that to keep it simple, the Bastard Injection pattern was used for the project template to avoid forcing a specific IControllerFactory upon developers.
If you use a DI framework (like Unity) and you active your controllers via the container, it might not find the dependencies and use the default constructor (in this case).
If you would like use use generics, something like ... where T : IController, new() you will need a default constructor.
Another reason for having a default (no parameter) constructor is for Reflection.
The classes in the System.Reflection namespace, together with Type, allow you to obtain information about loaded assemblies and the types defined within them, such as classes, interfaces, and value types. You can also use reflection to create type instances at run time, and to invoke and access them.
There might be times where you need to create a temporary object of that type in order to reflect over it's properties or methods, but don't want or need the overhead of creating a real object - especially if that entails accessing a database or remote service for example.