[PATCH] except doesn't work in different scopes

Here is my patch (with tests) for it.

I suggest moving order from MULTI_VALUE_METHODS to SINGLE_VALUE_METHODS and overwriting the order array with each merged scope or new call to order(). There's no benefit in using:

Employee.order(:division_name).order(:name)

over

Employee.order(:division_name,:name)

And the fact that both of the below calls return Posts by [:created_at,:title] order is just plain misleading:

class Post < ActiveRecord::Base
  default_scope order(:created_at)
  scope :by_title, order(:title)
end
Post.order(:title)
Post.by_title

Adam Wróbel, order is a multi value and I can give you a lot of examples from my real apps where you need to use queries like:

SELECT * from employers WHERE ORDER BY salary ASC, name ASC

Here you sort employers by salary and if salary is equal you sort then by name. It is a common task. And so if we're allow user to write order('salary ASC, name ASC') I think we should allow to write order(:salary).order(:name).

Adam Wróbel, i mean that it is not intuitive why we can do:

order(:division_name).order(:name)

and can't:

Employee.order(:division_name,:name)

or do something like:

class Post < ActiveRecord::Base
 scope popular, where('rating > 1').order('rating DESC')
 scope recent, order('created_at DESC')
end

Post.popular.recent

Oh, sorry, it is 2:57 AM here. In my previous comment we can't do first and can second and so can't do the last example with a Post class.

An alternative would be to overwrite on merge, but append on order(). That would be similar to where(:column => value). Multiple where() calls create OR but during a merge only the last one is left.

I know you specify multiple columns for order, but when I referred to multi and single values I meant values that get merged and values that get overwritten. My suggestion was to overwrite array of order columns from the current scope with array of order columns from the relation being merged in.

The Post.popular.recent example makes sense and might be a reason for why none of my suggestions should be used, but then again order is such a simple operation that it's easy to list all the columns you need in one place. Usually I'd just be confused that my last call to order wasn't the one used rather than happy that I was was able to merge two named order scopes. Take this test from rails tests (tests/cases/relations_test.rb):

def test_order_using_scoping
  car1 = CoolCar.order('id DESC').scoping do
    CoolCar.find(:first, :order => 'id asc')
  end
  assert_equal 'zyke', car1.name

  car2 = FastCar.order('id DESC').scoping do
    FastCar.find(:first, :order => 'id asc')
  end
  assert_equal 'zyke', car2.name
end

To me it reads "def test_we_have_a_bug". I mean - I've specified the order I want right there - in the call to find() - why do you do it reverse, rails?

Santiago Pastorino, Yes this code computes at evaluation time, but it doesn't matter. I think that there is no reason (point me if i'm wrong) to allow user to use except only inside lambdas. I understand that I need to use lambda when I use Time.now or something but here I need some additional knowledge about how except, order, where and etc works inside rails. I don't think that it is good. I've added to my patch test with scope with lambda like:

lambda { except(:order).order("name DESC") }

and test passes.

How it works and why I think we can calculate except at evaluation time. A've added a flag into the Relation that it is except and store what we want to except, so when we merge relations when calling the scopes we can figure out that we need to except some values.

Please, point me if I made a mistake somewhere.

Oops, I've found that my last uploaded patch wasn't good enough (I've uploaded the wrong diff, sorry). Here is the correct one.