HABTM Association causes sync() to save model.

[SirRawlins]

I've been experimenting today and found that if you have a HABTM association which is set through disposable such as tag_ids then the underlying active record will save itself when the setter for that attribute is invoked.

This means that calling sync() on disposable can inadvertently save the underlying record. This would presumably also happen with has_many associations of a similar nature that AR also likes to autosave.

This is a quirk with AR rather than anything specific to Disposable, but after a Gitter conversation with @apotonick he asked me to file this as a reminder to anyone.

[dmitry]

More on that: https://discuss.rubyonrails.org/t/inconsistent-collection-setter-behaviour-has-many-has-many-through/72404
Would be good to change this behavior in the next major versions of activerecord.