Prevents nil values to be saved in Mongoid document, removes them from existing documents when saving. Also fixes small issues with Mongoid aliases

mongoid-enhancements.rb

module Mongoid
  module Enhancements
    extend ActiveSupport::Concern
    
    module ClassHelpers
      # Set callbacks
      def enhance
        self.set_callback(:save, :before, "remove_unnecessary_fields")
        self.set_callback(:initialize, :after, "fill_boolean_fields")
      end
      
      # Get real attribute names
      def real_attribute_names
        self.fields.map { |_, x|
          (x.options[:as] || x.name).to_s
        }
      end
    end
    
    module InstanceHelpers
      # Fix json representation
      def as_json(options = {})
        options[:except] ||= {}
        options[:except].concat(self.class.attribute_names - self.class.real_attribute_names).uniq!
        options[:methods] ||= {}
        options[:methods].concat(self.class.real_attribute_names - self.class.attribute_names).uniq!
        super options
      end
      
      # Remove unnecessary fields
      def remove_unnecessary_fields
        self.class.fields.each { |key, field|
          # Now field is nil (or it is bool and false)
          if self.send(key).nil? || (field.options[:type] == Boolean && !field.options[:default] && self.send(key) == false)
            # Simply remove from attributes
            self.raw_attributes.delete(key)
            
            # Unset field in existing document if it was not nil
            if !self.new_record? && !self.send("#{key}_was").nil?
              self.unset(key)
            end
          end
        }
        true
      end
      
      # Set booleans to false instead of nil
      def fill_boolean_fields
        self.class.fields.select { |_, field| field.options[:type] == Boolean }.each { |key, field|
          self.send("#{key}=", false) if self.send(key).nil?
        }
      end
    end
    
    included do
      extend Mongoid::Enhancements::ClassHelpers
      include Mongoid::Enhancements::InstanceHelpers
      enhance
    end
  end
end