Make reference fields a proxy to allow access to field.id without dereferencing

[rozza]

When looking at any other value then trigger a dereference either directly or on the list.

refs: #61

[thedug]

Has anybody started this?

[rozza]

I havent started 0.9 development yet

[Fraggle]

Just to let you know, I'm interested in this feature as well.

[lwcolton]

+1 for this

[thedug]

Is 0.9 still in the works or is mongoengine stalled?

[bsherry]

+1 This would be a great addition for things like uniqueness checks in a list of referenceField's

[bond777]

+1

[MRigal]

Definitely a good optimization to have ! But I would rather release a 0.9 now and postpone this to a new release

[MRigal]

And it might be a good idea to have #490 in mind while implementing the concept for this issue

[smcclstocks]

Are we able to access a referencefield to obtain the ID & avoid the dereference overhead yet? Thanks.

+1