Use unity registered instance to inject dependency

Question

When using Redis, we create a ConnectionMultiplexer and from that GetDatabase() to get access to a given cache.

I want to configure Unity to do this as follows:

ConnectionMultiplexer redis = ConnectionMultiplexer.Connect("localhost");
container.RegisterInstance(redis);
container.RegisterType<IDatabase, redis.GetDatabase()>();

But not surprisingly that wont compile.

The only other way I can think of at the moment is to create a database factory class and pass that into my controllers instead of an IDatabase but that seems like overkill as I would just essentially be wrapping a wrapper:

 public static void RegisterComponents() {
    ConnectionMultiplexer redis = ConnectionMultiplexer.Connect("localhost");
    container.RegisterInstance(redis);
    RedisDatabaseFactory redisDbf = new RedisDatabaseFactory(redis);
    container.RegisterInstance(redisDbf);
    container.RegisterType<IRedisDatabaseFactory, RedisDatabaseFactory>();
}

MyController.cs

public MyController(IRedisDatabaseFactory rdbf){
  _db = rdbf.GetDatabase();
}

So short of using this overly verbose factory method, how can I use the methods of registered instances to create injectable dependencies for other objects?

Russ Cam · Accepted Answer · 2014-10-22 10:37:29Z

4

You can register a factory method for IDatabase using InjectionFactory:

container.RegisterType<IDatabase>(new InjectionFactory(c => redis.GetDatabase()));

answered Oct 22, 2014 at 10:37

Russ Cam

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4 Comments

rism Over a year ago

Perfect, I knew there had to be a shorthand.

Russ Cam Over a year ago

No worries. If you wanted to get the database from the registered ConnectionMultiplexer then you can resolve it from the container parameter (c in the above code)

rism Over a year ago

Do you mean like this: container.RegisterType<IDatabase>(new InjectionFactory(c => c.Resolve<ConnectionMultiplexer>().GetDatabase())); is that not the same thing? Or is there a different scope between that and your answer?

Russ Cam Over a year ago

Yes, that's what I mean. In reality, both ConnectionMultiplexer and IDatabase are thread safe and can be passed around so can be registered with singleton lifestyle, meaning the above has the same outcome as my answer. But it's worth knowing that in case you have services that do not have singleton lifestyle

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