在C＃中使用反射和通用属性

Question

I have a interface/class in my ASP.NET MVC application where all my generic repositories are referenced. This looks something like this:

public interface IDb
{
    IGenericRepository<Car> CarRepository { get; }
    ...
    IGenericRepository<User> UserRepository { get; }
}

My goal is to find all types in an assembly which implement a certain interface and then find the corresponding generic repository to fetch some objects from the database. This should work:

List<IVehicle> vehicleElements = new List<IVehicle>();

Type vehicleType = typeof(IVehicle);
Type dbType = typeof(IDb);
foreach (Type type in vehicleType.Assembly.GetTypes().Where(t => t.IsClass && t.GetInterfaces().Contains(vehicleType)))
    {
        PropertyInfo repositoryInfo = dbType.GetProperties().Where(p => p.PropertyType.GenericTypeArguments.Contains(type)).SingleOrDefault();
        if (repositoryInfo != null)
        {
            var repository = repositoryInfo.GetValue(this.db);
            // TODO: work with repository
        }
    }

return vehicleElements;

My problem is that I don't know how to cast the repository variable to the needed generic IGenericRepository... Any ideas?

Answer 1

What you want to do can't work, because in order to have a stronlgy typed repository you would need to know the type at compile time that implements your interface. But you only know it at runtime.

One solution is to introduce a non-generic repository.

Another solution is to use the dynamic keyword.

dynamic repository = repositoryInfo.GetValue(this.db);
repository.SomeMethod(...);

However, this means that the compiler no longer can check the code that involves this dynamic variable. In other words: If SomeMethod doesn't exist on the actual type of repository a runtime exception will be thrown instead of a compiler error.

Answer 2

I'd go with a base IRepository interface with the common methods you need to interact with in this code.

If that's not possible for some reason you could go with a loosely coupled approach by casting to dynamic or grabbing the methods you need via reflection.