[MODEL] Avoid making an update when no attributes are changed

[nilbus]

@dim0627 pointed out in #743 that calling update_attributes({}) on an ActiveRecord model instance triggers the before_save callback, even when there are no attributes to update. This results in an unnecessary empty update request to elasticsearch.

Using ActiveSupport's presence, it will act the same for both nil and {}, which are both ways Rails can express that there are no changes to save.

Closes #743

[dim0627]

Thank you for making PR for my problem though 🙏

I think this changes should use presence instead of .present?.
Or if (attributes_in_database = self.instance_variable_get(:@__changed_model_attributes)).present?.

Otherwise, boolean will be assigned to attributes_in_database.

[nilbus]

Fantastic catch. I had interpreted it as a boolean, but the tests were just telling me the same thing. 😄

[nilbus]

Tests updated and passing (locally).

[nilbus]

@dim0627 I should point out that this change only replaces the update call with an index call.

elasticsearch-rails/elasticsearch-model/lib/elasticsearch/model/indexing.rb

Lines 407 to 409 in d8859ae

	else
	index_document(options)
	end

This change makes the behavior more consistent, but is it actually going to be helpful to you?

[dim0627]

@nilbus
Yes, I confused Why don't called index_document!?.
Your change is looks good to me 👍
Thanks!

[estolfo]

@nilbus and @dim0627 thanks for your work on this! I've tested the changes locally and will merge.

[nilbus]

Thanks! 🎉