How to configure Ninject to enter the correct instance depending on the previously entered instance

Question

I cannot find the right words for my question, so I will let my code speak.

I have a repository:

class Repository { public Repository(DbContext ctx) { } } 

then I have the following bindings:

 Bind<IRepository>().To<Repository>(); Bind<DbContext>().To<UserStoreContext>().When... Bind<DbContext>().To<CentralStoreContext>().When... 

and then I have a class that should access

db <

 class Foo { public Repository(IRepository userRepo, [CentralStoreAttribute]IRepository centralRepo) { } } 

How do I configure two DbContext bindings DbContext that stores with the correct contexts (based on CentralStoreAttribute) are introduced into the Foo constructor?

Answer 1

Instead of relying on attributes in the right places, I usually create several types that are actually just aliases. This is useful because with Ninject (and presumably other IoC containers) we query dependencies by type.

So, if you need to “request” a user repository compared to the central one, I would create types that look like this:

 interface IRepository { /* methods and properties */ } interface IUserRepository : IRepository {} interface ICentralRepository : IRepository {} class Foo { public Foo(IUserRepository userRepo, ICentralRepository centralRepo) { // assign to fields } } 

I prefer this because then Ninject does not expire at all in my application, it is more declarative, and I think it is easier to remember than any agreement based approach, like the one you are trying.

Answer 2

I tried this in proving the concept, but in the end went in a different direction.

 Bind<IRepository>().ToMethod(x => { var repositoryType = x.Kernel .Get<IConfigObject>() .SomeStringPropertyDenotingTheRepository; switch (repositoryType ) { case "1": return (IRepository)new Repository1(); default: return (IRepository)new Repository2(); } }).InRequestScope(); 

While it was working, I never found out if it was using a single instance of IObjectB or creating an instance of a new instance - it should be pretty easy to understand. I figured he called ToMethod every time I used the DI on IRepository - not tested again.

Answer 3

Use the When(Func<IRequest, bool> condition) overload When(Func<IRequest, bool> condition) to check recursively if r.Target.IsDefined(typeof(TAttribute), false) true for a given request or one of its participants r.ParentRequest

Answer 4

 Bind<IRepository>().To<Repository>(); Bind<DbContext>().To<CentralStoreContext>() .When( context => context.Target != null && context.Target.GetCustomAttributes( typeof( CentralStoreAttribute ) ) != null ); // make the general binding after the more specific one Bind<DbContext>().To<UserStoreContext>();