Is build_ Syntactic Sugar?

Question

I'm learning rails, and can't find a good way to search for this, as Google doesn't like underscores. What's build_* do as a prefix? Does it make an initializer for whatever model you attach it to?

Answer 1

It is related to associations. You can use it on a child class's object to build the parent association. You can't use it the other way around.

class Puppy
  belong_to :dog
  attr_accessor :name
end

class Dog
  has_many :puppies
  attr_accessor :name
end

p = Puppy.new(name: "baby")
p.build_dog(name: "John)