Bumping to mongoid 5

[matheus208]

Pull request to add compatibility to Mongoid 5.

Changes:

• Since Mongoid 4, Versioning is not available out of the box, so I had to add a check before including it.
• Mongoid 5 complained about using the foreign_key id on has_* relations. So I changed it to send the related model's name instead (which is the standard way of doing it on Mongoid 5). This might break older versions.

All tests are passing (once again, using Mongoid 5. I haven't used older versions). Is there an easy way to test all Mongoid versions?

[davidsevcik]

Will have a look on testing it with older Mongoid.

[matheus208]

Okay... I found a bug with Mongoid 5. When you save an attribute of a nested model, it will push both the nested model and the change on the "changed?" list.

For efficiency reasons (I suppose), Mongoid uses this to only save what has been changed on the document so far, resulting in it trying to update the model AND the model's attribute on the same requests. Which Mongo does not like, throwing an error.

"Mongo::Error::OperationFailure: Cannot update **MODEL** and **MODEL_ATTRIBUTE** at the same time (16837)"

The only thing I can think of is drop the aliasing of :changed? and :changes and stick to using :changed_with_relations and :changes_with_relations.

That might be a deal breaker for this pull request being accepted... What are your thoughts on it?

[matheus208]

Also, I found a bug that is probably happening on the master branch as well.

When you save a document that has a has_one or has_many, Mongoid calls the after_save callback multiple times in an infinite loop and a stack level too deep error is thrown.

I'm trying to figure out why/fix it, but I'm having a hard time.

[mateuspontes]

@matheus208 hey, do you like to continue this PR? You removed alias_method_chain and I think it is good, but you cann't see relation_changes anymore without chain.