Lazy Loaded Proxies (more than just lazy loaded navigation properties)

[Wain123]

Since lazy loaded navigation properties are planned for a future version of EF Core, I'll consider them as a given here. I am looking for a feature similar to NHibernate's lazy loaded proxies. To be more specific:

I often want to set or read navigation properties and compare entities for equality. Example:
if(post1.Blog == post2.Blog)
In the above line, post1 and post2 are already loaded, but post1.Blog and post2.Blog might not be. I want to be able to do the comparison above without loading post1.Blog and post2.Blog from the database - essentially, I want to compare the foreign keys, by using a Blog entity as a "proxy".

Here's another example:
Blog b = post1.Blog;
post1.Blog may or may not have been loaded previously. If it was, b is a normal Blog. Otherwise, b is a proxy that has a primary key value but no property values.
post2.Blog = b;
Doesn't require DB access.
string s = b.URL;
If b isn't loaded yet, EF automatically gets b's property values from the DB, since one of them was requested.

The following workarounds are not satisfactory:

• Splitting the Blog table into two entities (or, since table splitting isn't in EF Core yet, into two tables and two entities) - one that has only the primary key and one that has the properties. I am unable to hide this hack in such a way that I can program with it as if it were a single entity.
• Letting the business logic know whether an entity is loaded or not. That would complicate my business logic. Also, primary keys and foreign keys are a DB concept that doesn't belong in business logic in the first place.

[giggio]

This is one of those things that should just work and that enable a good code writing experience. The ORM is almost invisible. This is a must. Good one!

[Wain123]

Maybe duplicate of #1387

[ajcvickers]

@Wain123 #1387 is a completely different feature. This feature is about not lazy-loading an entity when not needed; #1387 is about lazy-loading non-navigation properties.

[szpght]

This can be based on #997