Request: macros for making `NewPost` and `Post` structs less redundant

[rbalicki2]

Would it be possible for diesel to provide macros so that if I have two models, say Post and NewPost, which differ only in that Post also has an id field, I could define them using only a single struct?

e.g.

#[alsoDefineNew]
pub struct Post {
  #[excludeInNew] id: i32,
  title: String,
}

And now, there is a NewPost struct as well.

I've thought about doing this with traits, but it ends up being very redundant and OOP in a java-like way. Macros could probably help, though.

This is far above my pay grade right now, but I wanted to make this request - perhaps it already exists or is in the pipeline :)

[rbalicki2]

Come to think of it, this is not really core to diesel's mission. It's probably better as an external library. It might need to know about diesel's Insertable, etc. derivations, but otherwise would probably be best as a separate library.

[Eijebong]

Have a look at #860 too ^^

[behos]

I've created something along these lines for the new structure here

https://github.com/behos/models-derive

Used like https://github.com/behos/models-derive/blob/master/tests/default_insertable.rs#L20

but i haven't published this as a crate since I'm not 100% sure it's complete. I'd be happy to get some feedback and ideas/contributions around that