Does Mongoid Support Through Associations for has_one or belongs_to Relationships?

Mongoid indeed does not support the ActiveRecord-style mapping with a through option for either has_one or belongs_to associations. This means that the following declaration:

RUBYCopied
class Customer
  has_one :salesperson
  has_one :manager, through: :salesperson
end

class Salesperson
  has_one :manager
end

won't work because Mongoid's associations only accept the valid options listed (such as :class_name, :foreign_key, :dependent, etc.) and do not include a :through option for these types of relations.

If you need to access a manager through a salesperson, you'll have to handle it manually. For example, you can define a custom method in your model:

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class Customer
  include Mongoid::Document
  has_one :salesperson

  def manager
    salesperson&.manager
  end
end

class Salesperson
  include Mongoid::Document
  has_one :manager
end

This way, calling customer.manager will delegate the lookup to the associated salesperson without using an unsupported association macro.