Should be true if there is a foreign key present on the owner which references the target. This is used to determine whether we can load the target if the owner is currently a new record (and therefore without a key).
Currently implemented by belongs_to (vanilla and polymorphic) and has_one/has_many :through associations which go through a belongs_to
# File activerecord/lib/active_record/associations/association.rb, line 194 def foreign_key_present? false end