On 21/09/12 12:25 PM, Tomas Sedovic wrote:
On 09/20/2012 02:20 PM, Martyn Taylor wrote:
Gents.

I'm having some trouble with getting nested resources working properly
from bespoke XML/JSON in RESTful API.  There seems to be some
fundamental problems with the way rails works, which means we have to
write a lot of bespoke code to get it working, possibly even having to
monkey patch Rails itself.

I've written an example rails app that highlights the problem and put a
detailed description in the README you can find it here:

https://github.com/mtaylor/Rails-Nested-Resource-Issues

I've ran into this issue on IME.  But it's going to affect us across all
rails projects with REST APIs, so we could do with discussing this issue
and coming up with the best possible solution that results in as little
replication as possible.

Please read through the problem and let me know if you have any better
ideas that the solutions I have proposed.

Regards

Martyn


I'm beginning to lean towards the custom serialization and deserialization. We'll have explicit control over the input/output formats which is a good thing for API stability.

However, there may be another issue that's reasonably close to what we expected the default behaviour would be.

If I understand this correctly, the issue isn't really behaviour of the `attribute=` setters but of `Model.new`[1] and `@model.update_attributes`[2] methods.

We could insert a base class into the model inheritance chain and either "fix" the methods there or add new ones that do bulk attribute operations correctly.

Pseudocode:

class NestedModels < ActiveRecord::Base
  def initialize(attributes = nil, options = {})
    if attributes
      attributes = attributes.clone
      get_nested_attribute_names.each do |name|
        attributes[name + '_attributes'] = attributes[name]
    attributes.delete name
      end
    end
    super.initialize(attributes, options)
  end

  def update_attributes(attributes, options = {})
    # TODO, similar to initialize
  end

  def update_attributes!(attributes, options = {})
    # TODO, similar to update_attributes
  end

  def get_nested_attributes
    # TODO: use introspection to figure out attribute names passed to accepts_nested_attributes_for in the model declaration
  end
end

class User < NestedModels
  has_many :addresses

  accepts_nested_attributes_for :addresses
  attr_accessible :name, :addresses, :addresses_attributes
end


now calling:

    User.new({"name"=>"Joe Bloggs", "addresses"=>[{"street"=>"Church Street"}]})

would work because ActiveRecord::Base would receive:

    {"name"=>"Joe Bloggs", "addresses_attributes"=>[{"street"=>"Church Street"}]}


This is similar to the monkeypatching proposal but it's safer. We would not be modifying any of the Rails' internals. Rather, we'd explicitly specify which models should have this modified behaviour.

We could probably also do this by including a module with the overrides instead of using inheritance.

Keep in mind that ActiveRecord provides builder methods for associations [3]. In the example you used:

   User.address.build(:street => "Church street")

or if you already have an instance of User:

   @user.address.build(:street => "Church street")


There are similar methods for one-to-many associations, which have the benefit of elements of collection not being persisted immediately (as opposed to adding an element to a collection directly).


If you are inclined to solve the problem on the model level, you could add a factory method that accepts a hash, and returns a fully-assembled instance, nested resources and all, with no monkey patching involved.


-d




[1]: https://github.com/rails/rails/blob/9b5309fb6819d8f2a1b31e44ba61e682272c7aa3/activerecord/lib/active_record/base.rb#L481
[2]: https://github.com/rails/rails/blob/81542f95d25825a7d3eff87d6f706661bf553b18/activerecord/lib/active_record/persistence.rb#L211
[3]: http://api.rubyonrails.org/classes/ActiveRecord/Associations/ClassMethods.html