Ninject：同一类有两次以上的匹配绑定可用

Question

Given this class:

public class UserQueryHandler : 
    IQueryHandler<UserCredentialsByUsernameQuery, UserJWTIdentity>,
    IQueryHandlerAsync<UserRoleByUserNameQuery, UserRole>
{

//..implementation }

public interface IQueryHandler<TParameter, TResult>
{
    TResult Retrieve(TParameter query);
}
public interface IQueryHandlerAsync<TParameter, TResult>
{
    Task<TResult> RetrieveAsync(TParameter query);
}

And the following Ninject configuration:

kernel.Bind(x => x
       .FromThisAssembly()
       .SelectAllClasses().InheritedFrom(typeof(IQueryHandler<,>))
       .BindAllInterfaces());

            kernel.Bind(x => x
             .FromThisAssembly()
             .SelectAllClasses().InheritedFrom(typeof(IQueryHandlerAsync<,>))
             .BindAllInterfaces());

I'm getting the following error:

More than one matching bindings are available.

Matching bindings:

1) binding from IQueryHandlerAsync{UserRoleByUserNameQuery, UserRole} to UserQueryHandler

2) binding from IQueryHandlerAsync{UserRoleByUserNameQuery, UserRole} to UserQueryHandler

Activation path:

1) Request for IQueryHandlerAsync{UserRoleByUserNameQuery, UserRole}

When trying to get an instance using this:

var handler = _kernel.Get<IQueryHandlerAsync<UserRoleByUserNameQuery, UserRole>>();

The suspicious thing is that I don't get the error trying to instantiate the other interface implementation:

var handler = _kernel.Get<IQueryHandler<UserCredentialsByUsernameQuery, UserJWTIdentity>>();

And the error disapears if I create a separated class that implements only that interface:

public class UserQueryHandler2 : 
    IQueryHandlerAsync<UserRoleByUserNameQuery, UserRole>
{
//..implementation works fine!! }

From what I understand, the class is being binded twice, but I don't understand why is this happening (probably a bug?)

Answer 1

BindAllInterfaces is binding all the interfaces the type inherits from, which in the case of UserQueryHandler is both IQueryHandler and IQueryHandlerAsync . So your type is being bound to IQueryHandlerAsync in the first portion of your Ninject configuration when it's scanning for all types that inherit from IQueryHandler .