Add extra_returning_fields in apply

[kigawas]

Closes #730

[xnuinside]

@kigawas, hi! Good PR & additional feature.

@wwwjfy, @fantix, what do you think?

[wwwjfy]

Sorry for the late.

I'm thinking of a parameter to return/reload every column instead of specified ones only. It saves a get call, which is probably being used in such case now.

Another nitpicky point is the usage of tuple in this PR. As I understand, list is more suitable here, semantically. Quoting Python doc: Tuples are immutable sequences, typically used to store collections of heterogeneous data

[kigawas]

Yes. Tuple should be replaced by Sequence in Python, which sugguests an immutable sequence although you can still pass list.

I'm thinking of a parameter to return/reload every column instead of specified ones only. It saves a get call, which is probably being used in such case now.

It's certainly better to get all columns by default, but for now a transitional approach would be more realistic to avoid API change

[wwwjfy]

I don't mean that big a change, but just an additional parameter like update_all (need a good name) to return all columns and update the instance. Similar to the one in the PR, but no need to list every single one.