datastore: keys_only query should return Keys?

[pdknsk]

I don't know the answer to that question, but I'd like to suggest so. It's what ndb does. Right now, gcloud-python returns a key-only Entity. It's a minor issue either way as the key is just one property away.

[tseaver]

-1 for having the return type vary based on arguments: "queries return entities" is much easier to reason about than "queries return entities, except when they return keys."

[dhermes]

I'm -1 too.

@pdknsk WDYT about a separate method for keys only queries just like datastore.get and datastore.get_multi?

Also keep in mind #557 will be resolved someday.

[theacodes]

-1 as well, it was surprising at first because I was used to ndb, but really, keys only is a projection and it definitely makes sense to have query/get/get_multi always return entities.

[dhermes]

Will re-open if @pdknsk weighs in.