Mongoid greater than date or not nil

Question

I have two models

class Conversation
  include Mongoid::Document 

  field :last_moderated_at, type: DateTime
  has_many :messages
end

class Message
  include Mongoid::Document
  include Mongoid::Timestamps
end

I want to get the list of all messages that were created after the moderation date, or all of them if the moderation date is nil

I had expected the following to work

conversation.messages.where(
      :created_at.gte => conversation.last_moderated_at
    )

But apparently the comparison with nil fails (when last_moderated_at == nil)

Do I have no choice but to use an if/else or is there a mongoDB operator of type greater than that also works when compared to nil dates ?

EDIT : A simpler example : Conversation.where(:created_at.gte => nil).count will always return 0

Answer 1

I think you are gonna have to to something like this:

conversation = Conversation.find 'some_id'

Message.where(
      conversation: conversation,
      :created_at.gte => conversation.last_moderated_at
    )

Answer 2

The syntax is correct. It does work on Mongoid version 6, at least.