with_scope raising "MySQL::Error Unkown column" error in RoR 2.3.11

Given this model in legacy code, with RoR 2.3.11:

class Assignment < ActiveRecord::Base
  belongs_to :source_person 
  belongs_to :destination_person
  belongs_to :laptop

  def self.setScope(places_ids)
    find_include = [:laptop => {:owner => {:performs => {:place => :ancestor_dependencies}}}]
    find_conditions = ["place_dependencies.ancestor_id = (?)", places_ids]

    scope = { :find => { :conditions => find_conditions, :include => find_include } }
    Assignment.with_scope(scope) do
      yield
    end
  end
end

Whenever it reaches the Assignment.with_scope statement, I get the following exception:

 Assignment Delete all (0.0ms)   Mysql::Error: Unknown column 'place_dependencies.ancestor_id' in 'where clause': DELETE FROM `assignments` WHERE (`id` IN (17)) AND (place_dependencies.ancestor_id = (1)) 

My schema looks like this:

  create_table "assignments", :force => true do |t|
    t.date    "created_at"
    t.date    "date_assigned"
    t.time    "time_assigned"
    t.integer "source_person_id"
    t.integer "destination_person_id"
    t.integer "laptop_id"
    t.text    "comment"
  end

  add_index "assignments", ["destination_person_id"], :name => "assignments_destination_person_id_fk"
  add_index "assignments", ["laptop_id"], :name => "assignments_laptop_id_fk"
  add_index "ass开发者_如何学JAVAignments", ["source_person_id"], :name => "assignments_source_person_id_fk

  create_table "place_dependencies", :force => true do |t|
    t.integer "descendant_id"
    t.integer "ancestor_id"
  end

  add_index "place_dependencies", ["ancestor_id"], :name => "place_dependencies_ancestor_id_fk"
  add_index "place_dependencies", ["descendant_id"], :name => "place_dependencies_descendant_id_fk"

I have almost the same code across multiple models, but everything works fine there. Could you give me a hint, on how to tackle this issue?

After doing the following it works:

 def self.setScope(places_ids)
    find_include = {
      :laptop => {
        :owner => {
          :performs => {
            :place => :ancestor_dependencies}
        }
      }
    }
    find_conditions = {"place_dependencies.ancestor_id" => places_ids}

    Assignment.all :joins => find_include, :conditions => find_conditions
    yield
  end

This answer needs review from a more experienced Ruby on Rails developer.