Exception: Ohm::Model::MissingID

Raised when you try and get the id of an Ohm::Model without an id.

  class Post < Ohm::Model
    list :comments, Comment
  end

  class Comment < Ohm::Model
  end

  ex = nil
  begin
    Post.new.id
  rescue Exception => e
    ex = e
  end

  ex.kind_of?(Ohm::Model::MissingID)
  # => true

This is also one of the most common errors you’ll be faced with when you’re new to Ohm coming from an ActiveRecord background, where you are used to just assigning associations even before the base model is persisted.

  # following from the example above:
  post = Post.new

  ex = nil
  begin
    post.comments << Comment.new
  rescue Exception => e
    ex = e
  end

  ex.kind_of?(Ohm::Model::MissingID)
  # => true

  # Correct way:
  post = Post.new

  if post.save
    post.comments << Comment.create
  end