Proper way for property injection using Autofac

Question

I'm building a MVC application with Autofac and EntityFramework. I have a large set of data repositories / business objects that use my logging interface (NLog). I have just started working with Autofac and would like to know the preferred way for property injection:

• Pass ILogging as constructor property, for this I have to set each local property from the constructor and creates larger constructor footprints.
• Register each object individually with Autofac (they do not share a generic interface)
• Use an Autofac.Module to locate these objects and set the property with reflection
• Create a generic interface ILoggerDependency and register this with Autofac, this way all objects are easely registred.

My preferred method (out of lazyness...) is to have a generic interface that I can register with Autofac.

Answer 1

I am not that familiar with Autofac, so I'll try to give you my best recommendation based on what I know.

If there is one thing a lot of people gets wrong with dependency injection, it has to be using it for automation. The goal of DI is not to remove magic from your code. If anything, it is quite the opposite.

Keeping that in mind, I would not even consider using reflection as it hides large amounts of fragile plumbing.

Next, interfaces in OOP are meant to express what an object can do. Being injected is definitely not an action an object can take, but rather something that is imposed on an object. Even though, it is a quick and dirty way to solve your issue, I would refrain from using it as it will denature the structure of your code.

I have trouble understanding what you mean by pass ILogging as constructor property. Basically, you mean to resolve the interface yourself in the constructor? This looks a lot like property injection which defeats the purpose of DI by adding a strong dependency on your container within your class. Basically, instead of depending on Log4Net, you end up depending on Autofac. To fix this, you would need to add a service locator and then you still end up with a similar problem. How do you inject your service locator?

This is why I would register each object individually. It lets your container do its job. It doesn't affect your code structure and abstractions. It doesn't uses reflection (magic). It doesn't force you to depend on your container within each class. Besides, it also gives you a centralized place to look for when adding or removing repositories from your code.