Model with “method missing” behaves differently in Rails 4 than Rails 3 (can cause 'stack level too deep' error)

问题

I have a Rails application that was working fine with Rails 3.2.14. I have just started to work on upgrading it to Rails 4, essentially following along with Railscast episode 415.

I got as far as the part where I try to run my rspec tests to find many now fail with the following error:

 Failure/Error: Unable to find matching line from backtrace
 SystemStackError:
   stack level too deep

I also checked my Cucumber tests and find similar failures.

stack level too deep (SystemStackError)

As everything was fine before I started upgrading, I have been searching for other experiences that are similar but haven't found any.

I have tried both Ruby 1.9 and 2.0. I have not modified any code

Any guidance appreciated.

Update:

I have tracked the problem down to a model thatat defines method_missing as part of its implementation. I have described what I have found in a separate answer so that it can be commented on separately.

My application contained a model that implemented its own method_missing which could cause a recursive loop that ultimatly concluded in the "stack level to deep" error.

回答1:

Per suggestion, there is sufficient detail to warrant separating this as an answer.

I have tracked the problem down to a model that defines method_missing as part of its implementation. I have found that, if there is a method_missing definition in the model, then it is called instead of any accessors. This causes any model set-up to fail.

(in my specific case, method_missing was defined and this is what caused the stack overflow that I mentioned originally).

I can reproduce the problem succinctly by defining a new rails app in Rails 3.2.14 and then creating a new model:

class Item < ActiveRecord::Base
  attr_accessible :name, :content
  store :content

  def method_missing(id, *args) 
    puts "method missing: #{id}"
  end
end

and the associated migration

class CreateItems < ActiveRecord::Migration
  def change
    create_table :items do |t|
      t.string :name
      t.text :content

      t.timestamps
    end
  end
end

If I run a rails console I can exercise the model:

$ rails console
Loading development environment (Rails 3.2.14)
2.0.0p247 :001 > x = Item.new(name: 'foo')
 => #<Item id: nil, name: "foo", content: {}, created_at: nil, updated_at: nil> 
2.0.0p247 :002 >

If I build exactly the same thing in Rails 4.0.0 I get different output:

$ rails console
Loading development environment (Rails 4.0.0)
2.0.0p247 :001 > x = Item.new(name: 'foo')
method missing: name=
 => #<Item id: nil, name: nil, content: {}, created_at: nil, updated_at: nil> 
2.0.0p247 :002 >

You'll notice that, in Rails 3.2.14, the name attribute is set to foo as is the intention. In Rails 4.0.0, however, see that method_missing is called and the attribute is not set.

I am reading up on the changes to ActiveRecord but I haven't been able to find anything that suggests models using method_missing which were ok prior to Rails 4 would no longer be ok in Rails 4.

Any pointers to getting the code example able to work in Rails 4 would help me solve the problems that I have with my model.

UPDATE

By manually invoking the upward method_missing chain, I can get the above example to work:

  def method_missing(id, *args) 
    super
    if respond_to? id
      send(id,*args)
    else
      puts "method missing: #{id}"
    end 
  end

Needing to do this feels wrong to me because it isn't clear why this behaviour changed between Rails 3 and 4. I feel I am missing something else...

回答2:

I don't know what the change was either, but you can avoid calling super for non-accessor methods by checking respond_to_without_attributes?. This is used in the source

  def method_missing(method, *args) 
    super if respond_to_without_attributes?(method, true) # returns true when attr accessors

    if respond_to? method
      send(method,*args)
    else
      puts "method missing: #{method}"
    end 
  end

来源：https://stackoverflow.com/questions/18287707/model-with-method-missing-behaves-differently-in-rails-4-than-rails-3-can-cau

标签

rspec

upgrade

ruby-on-rails-4