Linq query not selecting a list of fields-CodePudding

I have three linq queries, the first one just gets a list of assembly types which works fine. The second one I am having issues with. It is returning 0 results and I am not sure why.

Here is a query the first query that I use that gets reused:

      var types = (
        from assemblies in AppDomain.CurrentDomain.GetAssemblies()
        from type in assemblies.GetTypes()
        select type
      ).ToList();

Next I have this query which returns 0 results and I am not sure why:

      var injectors = (
        from type in types
        from attrs in type.GetCustomAttributes<InjectAttribute>()
        select attrs
      ).ToList();

The third query is almost exactly the same as the second query only it selects a different attribute. This one works:

      (
        from type in types
        from attrs in type.GetCustomAttributes<InjectableAttribute>()
        where attrs.ProvidedIn == ProvidedIn.Root
        select type
      ).ToList().ForEach(service => {
        var injector = injectors.Find(i => i.serviceType == service);
        if (injector != null) {
          var newService = Activator.CreateInstance(service);
          services.Add(newService);
        }
      })

I am not sure why the second query works and the third does not...

Here is how I am using the two:

[Injectable(ProvidedIn = ProvidedIn.Root)]
public class Item { }

public class Test {
  [Inject(typeof(Item))] Item item = null;
}

What I am trying to achieve, is in the foreach loop if one of the fields in the project has a [Inject] attribute used with a particular type, then create an instance, otherwise don't create an instance. This is for a reusable classlib, so an inject type may or may not be used on the project that is consuming the library. If it isn't being used I don't want to create an instance of the [Injectable].

Side note: Is creating 3 separate Linq queries optimal, or I can I combine them into one query?

CodePudding user response：

Inject is applied to members, not the type. To look for types whose members have that attribute you can use :

where type.GetMembers()
          .SelectAny(mi=>mi.GetCustomAttributes<InjectAttribute>())
          .Any()