Support $useKeys option when EagerCursor converts to an array

[jmikola]

Fixes #160.

[jmikola]

@alcaeus: Can you take a look at this Monday?

[alcaeus]

The changes look good 👍
Do we want to expose this in the Builder or Query class so that it can be controlled by developers?

[jmikola]

Do we want to expose this in the Builder or Query class so that it can be controlled by developers?

@alcaeus: Possibly. At the moment, it appears the only way to specify $useKeys would be to let the query builder return a cursor and then invoke toArray() on it manually. The Query class' own toArray() method doesn't currently pass through the option. getSingleResult() does so, but that's simply because Cursor::getSingleResult() always sets it on its own.

This may be because we're being strict about Doctrine MongoDB's Iterator and IteratorAggregate interfaces, neither of whose toArray() methods take an argument.

[jmikola]

Although we discussed moving $useKeys to an initialize() parameter, integration with ODM would benefit from keeping this as a constructor argument. That is because ODM's Cursor class (if we remove its EagerCursor) will merely wrap a CursorInterface.