Ingesting data into MongoDB causes "stack level too deep"

Question

I have a bunch of records stored in a mongodb collection (StudentRecord). These need to be broken out into a Collection of type Student with the Embedded Document StudentGrade. For some reason, the rake task I'm using to do this ingestion keeps hitting a "stack level too deep". I can't detect any recursive calls and I'm using bundle exec to execute it (ruby 1.9.2-p320).

task :parse_student_records => :environment do
  StudentRecord.all.each{|student_record|
    student = Student.create({:name => student_record.name})
    student.grades « Grade.create({:score => student_record.grade_score)
    student.save!
  }
end


class Student
  include MongoMapper::Document
  many :grades
  key :name, String
end

class Grade
  include MongoMapper::EmbeddedDocument
  key :grade_score, String
end

Ingesting the documents as independent documents instead of embedded documents fixes it..for some reason, the embedding causes the problem.

Answer 1

That's issue 265, one of the few I know by number.

To get callbacks to fire on embedded documents in the correct order, MongoMapper has to build a huge stack that grows linearly with the number of embedded docs. At around ~600-800 docs, the stack overflows.

ActiveSupport::Callbacks is a huge mess and would require a rewrite to dodge the issue cleanly (it's less of a mess on Rails head, but still would need rewriting).

The current proposal in issue 265 is to disable the callbacks.

# in Gemfile
gem 'mongo_mapper', :git => 'git://github.com/jnunemaker/mongomapper.git', :ref => 'fefec91027f2dd8eb1ab9caa5a4b0acd000f4da7'

And then:

class Student
  include MongoMapper::Document
  embedded_callbacks_off
  # ...
end