问题
1) I know that it will save associations when autosave: true as per http://railsapi.com/doc/rails-v2.3.8/classes/ActiveRecord/AutosaveAssociation.html
2) I know that it will save associations that are constructed like
book = Book.new(name: 'foo')
book.authors.build(name: 'bar') #has_many
book.save
or like
book = Book.new(name: 'foo')
book.build_author(name: 'bar') #has_one
book.save
3) I think associations are also saved when they are assigned or added
book = Book.new(name: 'foo')
book.author = Author.new(name: 'bar')
book.save
or
book = Book.new(name: 'foo')
book.authors << Author.new(name: 'bar')
book.save
But, I have a complicated bug that involves something not auto-saving when I would expect it to. So, I want to debug by inspecting book to verify what I think is going to be saved will actually be saved.
TL; DR;
What internal state is checked when saving associations? I'm assuming that a model has an internal instance variable like associations_to_save that associations get added to when they are created. Then, when the model is saved, it loops through those associations and saves them too.
回答1:
Unfortunately there are no such thing like associations_to_save. However there are some rules saying what is being saved when. You can find those here: http://guides.rubyonrails.org/association_basics.html. Points: 4.1.5 (belongs_to), 4.2.5 (has_one), 4.3.4 (has_many) and 4.4.4 (habtm).
UPDATE:
In case of has_many association, the child is saved on saving the parent if child.new_record? returns true (child was not yet saved to db), or the foreign_key column needs to be updated. This is why:
- Adding object to association on saved parent do save new child.
- Adding object to association on unsaved parent doesn't save (no foreign key value)
- If unsaved parent is being saved and has some child objects in association cache, those objects are saved to update foreign_key.
回答2:
Not sure if this will help anyone else, but I recently ran into a similar issue recently in Rails 5.2.
When trying to save an object 2 layers deep my tests failed if the top level and the first level objects had already been saved. Ie.
book_cover.persisted? == true
book_cover.book.persisted? == true
page = book_cover.book.pages.new
page.persisted? == false
# After saving the top level object
book_cover.save
page.persisted? == false
# After saving the immediate parent of page
book_cover.book.save
page.persisted? == true
Since the parent "book cover" wasn't the direct parent of the new object "page" saving "book cover" didn't actually end up saving the "page" object.
Depending on the situation I just explicitly called save on the "book" object to save all the child objects.
来源：https://stackoverflow.com/questions/18703036/when-will-activerecord-save-associations