Rails - avoid autosave in association

Question

My models and its associations are:

class Post < ActiveRecord::Base
  has_many :comments
end

class Comment < ActiveRecord::Base
  belongs_to :post
  validates :commenter, :presence => true
end

Case1: Automatically save method is called when I tried below code.

@post = Post.find(3)
@comments = @post.comments
p @comments #=> []
p @comments.class #=> Array
if @comments.empty?
  3.times do
    @comments << @post.comments.build
 end
end
p @comments.first.errors #=>{:commenter=>["can't be blank"]}

Case2: if I manually initialize same empty array to the @comments, auto save is not calling. for instance,

p @comments #=> []
p @comments.class #=> Array
if @comments.empty?
  @comments = []
  p @comments #=> []
  3.times do
    @comments << @post.comments.build
  end
end
p @comments.first.errors #=>{}

What is the best solution to avoid auto save and please any one explain why the above code behave differently?

Answer 1

Rails extensively uses monkey-patching, so rails Array is not the same thing as pure Ruby array. (Compare output from irb > [].methods and rails c > [].methods

According to the documentation << method of has_many collection

instantly fires update sql without waiting for the save or update call on the parent object

So most likely Rails have an "observer" of the collection events, and fires validation when you try to add new object.

In second snippet you use pure array (not has_many collection), so the update action is not fired.

To avoid update action you don't need << at all

@post = Post.find(3)
@comments = @post.comments
if @comments.empty?
  3.times do
    @post.comments.build
 end
end
p @comments.size
=> 3

Answer 2

Autosave is defined in the Post model. Read here about Autosave. If I understand your question correctly, then it should be enough to define :autosave => false.