DbFunctions: instance functions on entities

[divega]

Consider the scenario originally described at #9213 (comment) (about why instance functions on DbContext can be compelling):

db.Posts.Where(p => db.PostReadCount(p.Id) > 5);

It could actually be even more compelling to be able to do this:

db.Posts.Where(p => p.ReadCount() > 5);

This could work for instance methods, computed properties or even extension method defined over the entity type.

It would be convenient for the translation to automatically map the "this" entity instance to the key of the entity when invoking the database implementation of the function.

[ajcvickers]

@pmiddleton Let us know if you're interested in working on this.

[pmiddleton]

Yes

[regul4rj0hn]

Please also consider an scenario like the following: I need to efficiently check some information that is encrypted by a symmetric key in the database, across several tables.

It would be nice if we could do something like _dbContext.IsEmailAvailable(email) given the mapping of scalar function in the DB to the context:

[DbFunction("IsEmailAvailable", "dbo")]
public static bool IsEmailAvailable(string Email) => throw new NotImplementedException();

You don't always need to execute the function over an specific Entity.

Thanks

[pmiddleton]

@regul4rj0hn - Is email bound to an entity in your example? If so then you can already do that today.

If email is just a string coming in from the application then you can't. Support for use case is included in #11129 but that is on hold pending the query redesign in 3.0

[regul4rj0hn]

Yeah, it's coming from the app that's the issue. Currently calling the scalar function the old-fashioned way as a work around. I guess that refactor will have to wait then. Thanks for the help, @pmiddleton !