How can I assign without using self.attribute = in rails?

SO,

I have been working on this for a while, I posted a much larger question that didn't get any replies, but I'll ask a much simpler one here.

My question is, how else can I assign something without using self.attribute = in the following context:

 def photo_from_url(url)
   remote_photo = open(url)
   def remote_photo.original_filename;base_uri.path.split('/').last; end
   **self.photo = remote_photo**
   self.save
 end

I need to make photo_from_url a class method so I can call it from delayed_job however when I add self, it gives me "no method found photo=".

Please help开发者_运维问答! Thanks in advance...

---

Option 1: you want to create new object each time you call this method:

class Photo < ActiveRecord::Base
  def self.photo_from_url(url)
    ...

    new(:photo => remote_photo).save!
  end
end

Option 2: you want to update existing object, then you need to get object id you want to modify:

class Photo < ActiveRecord::Base
  def self.photo_from_url(url)
    ...

    id = # here you find id, e.g. from url 
    find(id).update_attributes!(:photo => remote_photo)
  end
end

---

A class method, by definition, does not reference any specific object instance. Therefore, you must have a way to get the object you want to modify. The simplest solution would be to pass a reference of that object into your class method and use that instead of self.

class Foo
  def self.photo_from_url(url, obj)
     ... 
     obj.photo = remote_photo
     ...
  end
end

Example usage:

foo = Foo.new # creates a new instance of Foo
Foo.photo_from_url("http://example.com/photo/12341", foo)

Notice how I am calling photo_from_url as a class method? That is because it is operating on the Foo class and not an instance of Foo, which happens to be foo here.

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Here is some literature on the difference between class and instance methods:

Class and Instance Methods in Ruby