Create an array of ids with rails

I am trying to create an array of ids so that I can query if a certain id is associated with an object. Here is my method but it isnt adding id's to the array.

class Report
  include Mongoid::Document

  has_and_belongs_to_many :reportapprovals, class_name: "Reportapproval", inverse_of: :report

  def bind_reportapproval
    @reportapprovals = Reportapproval.where(tenant_id: self.tenant_id).all

    if @reportapprovals.present? && @reportapprovals.any? { |ra| ra.tenant_approved == true }
      @reportapprovals.each do |ra|
        self.reportapproval_ids = ra.id
      end
    end
  end
end

This is suppose to add an array of reportapproval_ids to the report object.

via Chebli Mohamed