Rails 4: composed_of mapping to JSON store attribute - ruby-on-rails-4

Question

I have the following models set up
# task.rb
class Task << AR
# everything all task objects have in common
end
# login_request.rb
class Tasks::LoginRequest < Task
store :data, accessors: [:email, :first_name, :last_name, :expires_at]
composed_of :valid_until, class_name: 'DateTime', mapping: %w(expires_at to_s), constructor: Proc.new { |date| (date && date.to_datetime) || DateTime.now }, converter: Proc.new { |value| value.to_s.to_datetime }
end
I'm using the datetime_select helper in my form:
# _form.html.haml
= f.datetime_select :valid_until
This works quite well, but when I call update in my controller with the submitted form data I get the following error message:
1 error(s) on assignment of multiparameter attributes [error on assignment [2014, 4, 2, 9, 48] to valid_until (can't write unknown attribute 'expires_at')]
So, I'm guessing the updated method tries to manipulate the attributes hash directly, but obviously it can't find the attribute expires_at, since it's a simple accessor method of the JSON column data.
I know I could simply add this field to the DB and it would probably work - although there's no need then to have a composed_of statement. But I'd rather not go this route, because not every task has a expires_at column.
How can I overcome this error? Or did I miss something?

Answer 1

Currently compose_of is not supporting this scenario since it writes directly to attributes that are assumed to be in the database. I wrote a tweaked compose_of version that does (based of Rails 4.0.2 version)
Putting this in initialize folder:
#/initialize/support_store_in_composed_of.rb
module ActiveRecord
module Aggregations
extend ActiveSupport::Concern
def clear_aggregation_cache #:nodoc:
#aggregation_cache.clear if persisted?
end
module ClassMethods
def composed_of_with_store_support(part_id, options = {})
options.assert_valid_keys(:class_name, :mapping, :allow_nil, :constructor, :converter, :store)
name = part_id.id2name
class_name = options[:class_name] || name.camelize
mapping = options[:mapping] || [ name, name ]
mapping = [ mapping ] unless mapping.first.is_a?(Array)
allow_nil = options[:allow_nil] || false
constructor = options[:constructor] || :new
converter = options[:converter]
reader_method(name, class_name, mapping, allow_nil, constructor, options[:store])
writer_method(name, class_name, mapping, allow_nil, converter, options[:store])
create_reflection(:composed_of, part_id, nil, options, self)
end
private
def reader_method(name, class_name, mapping, allow_nil, constructor, store=nil)
define_method(name) do
if #aggregation_cache[name].nil? && (!allow_nil || mapping.any? {|pair| !read_attribute(pair.first).nil? })
if store.present?
attrs = mapping.collect {|pair| send(pair.first)}
else
attrs = mapping.collect {|pair| read_attribute(pair.first)}
end
object = constructor.respond_to?(:call) ?
constructor.call(*attrs) :
class_name.constantize.send(constructor, *attrs)
#aggregation_cache[name] = object
end
#aggregation_cache[name]
end
end
def writer_method(name, class_name, mapping, allow_nil, converter, store=nil)
define_method("#{name}=") do |part|
klass = class_name.constantize
unless part.is_a?(klass) || converter.nil? || part.nil?
part = converter.respond_to?(:call) ? converter.call(part) : klass.send(converter, part)
end
if part.nil? && allow_nil
mapping.each { |pair| self[pair.first] = nil }
#aggregation_cache[name] = nil
else
if store.present?
mapping.each { |pair| send("#{pair.first}=", part.send(pair.last)) }
else
mapping.each { |pair| self[pair.first] = part.send(pair.last) }
end
#aggregation_cache[name] = part.freeze
end
end
end
end
end
end
And using it like this would solve your problem.
class Task < ActiveRecord::Base
store :data, accessors: [:email, :first_name, :last_name, :expires_at]
composed_of_with_store_support :valid_until, class_name: 'DateTime', mapping: %w(expires_at to_s),
constructor: Proc.new { |date| (date && date.to_datetime) || DateTime.now },
converter: Proc.new { |value| value.to_s.to_datetime },
store: true
end