Fix eager_loading? when ordering with Hash syntax

[intrip]

Summary

eager_loading? is triggered correctly when using order with hash syntax on an outer table.

before:

Post.includes(:comments).order({ "comments.label": :ASC }).eager_loading?
=> raises ActiveRecord::StatementInvalid

after:

Post.includes(:comments).order({ "comments.label": :ASC }).eager_loading?
=> true

[intrip]

@ghiculescu can you please take a look at this fix? 🙇

[ghiculescu]

👍 it looks good to me.

[eugeneius]

Suggested change

	references = order_args.map do |arg|
	case arg
	when String
	arg
	when Hash
	arg.keys
	end
	end.flatten
	references = order_args.flat_map do |arg|
	case arg
	when String
	arg
	when Hash
	arg.keys
	end
	end

If any of the hash's keys are arrays, we don't want to flatten them.

[intrip]

@eugeneius Thanks!

I've applied the suggestion but the above use case it's unclear to me: could you show me an example of using Array as Hash keys for order? I've tried but I couldn't manage to reproduce.

[eugeneius]

I wasn't concerned about breaking a valid use case, more just that flat_map corresponds better to what we're trying to do here. Using flap_map also saves an intermediate array allocation so it should be (marginally) faster, which is probably worthwhile since this code runs every time a relation with an order is built.

[eugeneius]

Thanks @intrip!