validate and update single attribute rails

Question

I have the following in my user model

attr_accessible :avatar, :email

validates_presence_of :email
has_attached_file :avatar # paperclip

validates_attachment_s         


        

Answer 1

You could validate the attribute by hand and use update_attribute, that skips validation. If you add this to your User:

def self.valid_attribute?(attr, value)
  mock = self.new(attr => value)
  if mock.valid?
    true
  else
    !mock.errors.has_key?(attr)
  end
end

And then update the attribute thusly:

if(!User.valid_attribute?('avatar', params[:user][:avatar])
    # Complain or whatever.
end
@user.update_attribute('avatar', params[:user][:avatar])

You should get your single attribute updated while only (manually) validating that attribute.

If you look at how Milan Novota's valid_attribute? works, you'll see that it performs the validations and then checks to see if the specific attr had issues; it doesn't matter if any of the other validations failed as valid_attribute? only looks at the validation failures for the attribute that you're interested in.

If you're going to be doing a lot of this stuff then you could add a method to User:

def update_just_this_one(attr, value)
    raise "Bad #{attr}" if(!User.valid_attribute?(attr, value))
    self.update_attribute(attr, value)
end

and use that to update your single attribute.