[MODEL] Fix sort order on ActiveRecord >= 5

[jazzytomato]

This is addressing an issue in #546

The monkey patching regarding sort order was not removed when calling order on ActiveRecord versions >= 5.

The code introduced in #618 did not change the order method, this patch fixes it.

I have added a test that fails without my new code. The problem with testing the order with .first is that it applies the sql LIMIT 1, which would return a collection of 1 item from the database. But we want to test the order of the collection returned. Therefore, I added a test for the first item of the collection with [0] which doesn't limit the results returned from the db.

[estolfo]

Thanks @jazzytomato !

[estolfo]

@jazzytomato If I understand your comment correctly, #546 is not fully fixed with this PR, right?

[jazzytomato]

@estolfo Indeed, there is another issue which is a bit more involved.

The .order method is broken when sent to ActiveRecord ::Relation instead of Elasticsearch::Model::Response::Records, i.e. this will work

Model.search('abc').order('id desc')

but this will not work

Model.search('abc').distinct.order('id desc')

My comment here explains it in more details: #546 (comment)

[estolfo]

@jazzytomato
I believe this pull request resolves the issue: #835
I had to test if there was an order defined on the ActiveRecord query before applying the order of ids returned by the Elasticsearch query. Please test it and let me know if it works for you. Thanks for all your help on this!