issue-3144.rb

Mongoid.connect_to 'mongoid-3144'

class Post
  include Mongoid::Document
  field :name
  
  embeds_many :comments
  accepts_nested_attributes_for :comments

  # This line somehow triggers the bug; commenting it out fixes the bug, wierd.
  has_many :children, class_name: 'Item', foreign_key: :parent_id, inverse_of: :parent
  
  # This on it's own doesn't cause the bug.
  belongs_to :parent, class_name: 'Item', inverse_of: :children, index: true
end

class Comment
  include Mongoid::Document
  embedded_in :post

  field :title
end

post = Post.create({
  "name" => "A post",
  "comments_attributes" => {
    "0" => { "title" => "Comment 1" }
  }
})

post.reload

post.update({
  "name" => "A post!",
  "comments_attributes" => {
    "0" => { "title" => "Comment 1!", "id" => post.comments.first.id },
    "12345" => { "title" => "New Comment 2!" }
  }
})

puts
puts "The following counts should both be 2 but the last comment is not"
puts "being persisted. Commenting out the 'has_many :children' line in the"
puts "Post model fixes the bug, WTF?"
puts
puts "  * count: #{post.comments.count}, comments: " + post.comments.map(&:title).inspect
post.reload
puts "  * count: #{post.comments.count}, comments: " + post.comments.map(&:title).inspect
puts

Post.destroy_all