IAnnotatable.FindAnnotation does not find annotations recursively

[obohaciak]

When calling FindAnnotation on a derived entity type, the annotations declared on the base type are not returned.

Steps to reproduce

Consider following model:

EntityType: BaseType Abstract
  ... (cut for brevity)
  Annotations: 
    MyAnnotation: System.String

EntityType: DerivedType Base: BaseType

Searching for the annotation on derived type:

IEntityType derivedEntityType = model.FindEntityType(typeof(DerivedType).FullName);
// GetAnnotations below returns Count = 0
IEnumerable<IAnnotation> annotations = derivedEntityType.GetAnnotations();
// FindAnnotation below returns null
IAnnotation annotation = derivedEntityType.FindAnnotation("MyAnnotation");

Whereas, searching for the annotation on base type:

IEntityType baseEntityType = model.FindEntityType(typeof(BaseType).FullName);
// GetAnnotations below returns Count = 1
IEnumerable<IAnnotation> annotations  = baseEntityType.GetAnnotations();
// FindAnnotation below returns MyAnnotation
IAnnotation annotation = baseEntityType.FindAnnotation("MyAnnotation");

If we compare it analogous FindProperty, and FindDeclaredProperty, perhaps this FindAnnotation should have been FindDeclaredAnnotation instead to highlight the fact it searches the given type only whereas "FindAnnotation" implies that it works recursively.

It would be a (limited?) breaking change though, so perhaps something for a major release like .NET 5?

Further technical details

EF Core version: 3.1.1
Database provider: Microsoft.EntityFrameworkCore.SqlServer
Target framework: .NET Core 3.1
Operating system: Windows 10.0.18363.720
IDE: Visual Studio 2019 Enterprise 16.5.0

[obohaciak]

A little correction, GetAnnotations also doesn't work recursively.

[ajcvickers]

@obohaciak This is currently by-design. Can you explain a bit more about why you need them to be recursive?

[AndriySvyryd]

The difference between properties, navigations and annotations is that there can only be 1 property or navigation with the same name in a hierarchy, but there can be more than 1 annotation with the same name.

[obohaciak]

@ajcvickers Of course, I'll try to explain. I was inspired by an example given by @rowanmiller in #7586 in which he shows how to use custom annotations to add support for read-only entities. My case is similar - track entities strongly related to each other, much like a composition relationship. E.g. an entity EnginePart exists within and cannot exist without an Engine. However Engine is an abstract type, a base type of larger type hierarchy with derived types like CarEngine or PlaneEngine. The custom annotation may exist on any level in the hierarchy. I therefore need to walk the inheritance chain and ask each entity type if it defines the annotation. I hope that that makes sense.

I understand though that as @AndriySvyryd noted, an annotation can be defined multiple times in the type hierarchy and the result of FindAnnotation could therefore be ambiguous, dependent on the type at runtime.

[ajcvickers]

@obohaciak Thanks for additional info. Closing this as by-design for now.