Question

Does pushing an entity to a it’s parent collection causes the collection to be loaded?

e.g.:

Parent.childs << a_child

Is the parent.childs “array” now loaded with ALL the childs or just “a_child” ? i.e. will a SQL “select * from childs where parent_id = ?” statement will be executed before adding to the collection?

EDIT:

http://apidock.com/rails/v3.2.3/ActiveRecord/Associations/CollectionAssociation/concat_records seems to call “add_target” BEFORE calling “insert_record” which adds the entity to the @target array…

Answer 1

No (thank god)! Parent.childs is a Proxy and ‘<<‘ will just trigger the creation/update of a_child

More info on How do rails association methods work?

Also in the rails comments of associations/collection_associations.rb

You need to be careful with assumptions regarding the target: The
proxy does not fetch records from the database until it needs them,
but new ones created with +build+ are added to the target. So, the
target may be non-empty and still lack children waiting to be read
from the database. If you look directly to the database you cannot
assume that’s the entire collection because new records may have been
added to the target, etc.

A quick check on my console confirmed there the children aren’t loaded.

parent.children << child; nil

=> only parent and child where loaded….