So this is the predicament. I know the embeds_many allows you to embed documents into a parent document. This makes sorting by relations easier. However, I cannot have this, because my objects can be isolated entities. In other words, a contact cannot embed_many leads because a lead can exist independently of a contact.

So the relationship I created is a has_one:

class Contact
include Mongoid::Document
has_one :lead

field :reference_number, type: String
end

class Lead
include Mongoid::Document
belongs_to :contact
end

It works fine, until I need to sort leads by contact reference number. Then I do not know how this can be done.

In ActiveRecord, you can do this:

Lead.joins(:contact).order('reference_number asc')
Lead.joins(:contact).order('reference_number desc')

But there is no way to sort by relations in Mongoid:

contact_ids = Contact.order('reference_number asc').pluck :id
Lead.in(contact_id: contact_ids)

The above doesn't work. Any idea how to improve this problem?