Allow dot notation indices of embedded documents

[stillinbeta]

I mentioned earlier on the mailing list that I wanted to index embedded documents, as Mongo allows, and I was curious as to weather it was possible. It wasn't, so I did my best to fix it.

I made sure to preserve column aliases at the root level, but in the case of embedded models I do not currently check for aliases. Is this an important feature, or is what I've written reasonable?

[jonashaag]

We should also recurse in to embedded models. I can definitely help you with implementation if you're stuck.

[stillinbeta]

I wasn't stuck, it was just 2am and I was tired :)

[jonashaag]

Gna. I wanted the diff show this: https://github.com/django-mongodb-engine/mongodb-engine/compare/master...issue77

I think that makes the find_field code a bit easier to understand/parse. What do you think?

[stillinbeta]

I'm not sure how I feel about using is_instance. I used hasattr because I think in Python an "interface" should be determined by having attributes, not by checking superclass. For example, an element is iterable if it has an __iter__ method, not because it subclasses something.

I'm far from a python grandmaster though, and my intuition could be way off. Thoughts?

[jonashaag]

Ellie: It's clearer with isinstance. With hasattr, we'd need to explicitly mention what this attribute is about in a comment.

[OT]Python is duckly typed in theory but (in my opinion) misses some important constructs (like interfaces) to make type checks usable (for example, there's no straightforward duckly way to check for a string/unicode/list/dict etc). That's why nobody uses duck-type-checks in practice. The only exception I know about is hasattr(thing, 'read') --> thing is a file which is so wide-spread that everybody understands.[/OT]

Besides that, I'm not totally happy with how get_column_name is implemented (the replace list items in-place thing bugs me), so I'm still happy to accept improvements.

@flaper87 do you have some time to review my patch?

[stillinbeta]

Ok, fair enough. I'll pull your commit in and push, I think that's the appropriate workflow?

[jonashaag]

If you want to change anything, yes. Otherwise I can just merge my branch into master.

[stillinbeta]

My pep8 changes were done after you forked my branch, so I'll need to push with those.