Created an unscope method for removing relations from a chain of

relations. Specific where values can be unscoped, and the unscope method
still works when relations are merged or combined.

activerecord/CHANGELOG.md

@@ -1,5 +1,21 @@
 ## Rails 4.0.0 (unreleased) ##
 
+*   Added functionality to unscope relations in a relations chain. For
+    instance, if you are passed in a chain of relations as follows:
+
+        Posts.select(:name => "John").order('id DESC') 
+
+    but you want to get rid of order, then this feature allows you to do:
+
+        Posts.select(:name => "John").order("id DESC").unscope(:order)
+            == Posts.select(:name => "John")
+
+    The .unscope() function is more general than the .except() method because
+    .except() only works on the relation it is acting on. However, .unscope()
+    works for any relation in the entire relation chain.
+
+    *John Wang*
+
 *   Postgresql timestamp with time zone (timestamptz) datatype now returns a
     ActiveSupport::TimeWithZone instance instead of a string
 

activerecord/lib/active_record/relation/query_methods.rb

@@ -317,6 +317,67 @@ def reorder!(*args) # :nodoc:
       self
     end
 
+    VALID_UNSCOPING_VALUES = Set.new([:where, :select, :group, :order, :lock,
+                                     :limit, :offset, :joins, :includes, :from,
+                                     :readonly, :having])
+
+    # Removes an unwanted relation that is already defined on a chain of relations.
+    # This is useful when passing around chains of relations and would like to
+    # modify the relations without reconstructing the entire chain.
+    #
+    #   User.all.order('email DESC').unscope(:order) == User.all
+    #
+    # The method arguments are symbols which correspond to the names of the methods
+    # which should be unscoped. The valid arguments are given in VALID_UNSCOPING_VALUES.
+    # The method can also be called with multiple arguments. For example:
+    #
+    #   User.all.order('email DESC').select('id').where(:name => "John")
+    #       .unscope(:order, :select, :where) == User.all
+    #
+    # One can additionally pass a hash as an argument to unscope specific :where values.
+    # This is done by passing a hash with a single key-value pair. The key should be
+    # :where and the value should be the where value to unscope. For example:
+    #
+    #   User.all.where(:name => "John", :active => true).unscope(:where => :name)
+    #       == User.all.where(:active => true)
+    #
+    # Note that this method is more generalized than ActiveRecord::SpawnMethods#except
+    # because #except will only affect a particular relation's values. It won't wipe
+    # the order, grouping, etc. when that relation is merged. For example:
+    #
+    #   Post.comments.except(:order)
+    #
+    # will still have an order if it comes from the default_scope on Comment.
+    def unscope(*args)
+      check_if_method_has_arguments!("unscope", args)
+      spawn.unscope!(*args)
+    end
+
+    def unscope!(*args)
+      args.flatten!
+
+      args.each do |scope|
+        case scope
+        when Symbol
+          symbol_unscoping(scope)
+        when Hash
+          scope.each do |key, target_value|
+            if key != :where
+              raise ArgumentError, "Hash arguments in .unscope(*args) must have :where as the key."
+            end
+
+            Array(target_value).each do |val|
+              where_unscoping(val)
+            end
+          end
+        else
+          raise ArgumentError, "Unrecognized scoping: #{args.inspect}. Use .unscope(where: :attribute_name) or .unscope(:order), for example."
+        end
+      end
+
+      self
+    end
+
     # Performs a joins on +args+:
     #
     #   User.joins(:posts)
@@ -762,6 +823,39 @@ def build_arel
 
     private
 
+    def symbol_unscoping(scope)
+      if !VALID_UNSCOPING_VALUES.include?(scope)
+        raise ArgumentError, "Called unscope() with invalid unscoping argument ':#{scope}'. Valid arguments are :#{VALID_UNSCOPING_VALUES.to_a.join(", :")}."
+      end
+
+      single_val_method = Relation::SINGLE_VALUE_METHODS.include?(scope)
+      unscope_code = :"#{scope}_value#{'s' unless single_val_method}="
+
+      case scope
+      when :order
+        self.send(:reverse_order_value=, false)
+        result = []
+      else
+        result = [] unless single_val_method
+      end
+
+      self.send(unscope_code, result)
+    end
+
+    def where_unscoping(target_value)
+      target_value_sym = target_value.to_sym
+
+      where_values.reject! do |rel|
+        case rel
+        when Arel::Nodes::In, Arel::Nodes::Equality
+          subrelation = (rel.left.kind_of?(Arel::Attributes::Attribute) ? rel.left : rel.right)
+          subrelation.name.to_sym == target_value_sym
+        else
+          raise "unscope(where: #{target_value.inspect}) failed: unscoping #{rel.class} is unimplemented."
+        end
+      end
+    end
+
     def custom_join_ast(table, joins)
       joins = joins.reject { |join| join.blank? }
 

activerecord/test/cases/relation_scoping_test.rb

@@ -424,6 +424,150 @@ def test_order_after_reorder_combines_orders
     assert_equal expected, received
   end
 
+  def test_unscope_overrides_default_scope
+    expected = Developer.all.collect { |dev| [dev.name, dev.id] }
+    received = Developer.order('name ASC, id DESC').unscope(:order).collect { |dev| [dev.name, dev.id] }
+    assert_equal expected, received
+  end
+
+  def test_unscope_after_reordering_and_combining
+    expected = Developer.order('id DESC, name DESC').collect { |dev| [dev.name, dev.id] }
+    received = DeveloperOrderedBySalary.reorder('name DESC').unscope(:order).order('id DESC, name DESC').collect { |dev| [dev.name, dev.id] }
+    assert_equal expected, received
+
+    expected_2 = Developer.all.collect { |dev| [dev.name, dev.id] }
+    received_2 = Developer.order('id DESC, name DESC').unscope(:order).collect { |dev| [dev.name, dev.id] }
+    assert_equal expected_2, received_2
+
+    expected_3 = Developer.all.collect { |dev| [dev.name, dev.id] }
+    received_3 = Developer.reorder('name DESC').unscope(:order).collect { |dev| [dev.name, dev.id] }
+    assert_equal expected_3, received_3
+  end
+
+  def test_unscope_with_where_attributes
+    expected = Developer.order('salary DESC').collect { |dev| dev.name }
+    received = DeveloperOrderedBySalary.where(name: 'David').unscope(where: :name).collect { |dev| dev.name }
+    assert_equal expected, received
+
+    expected_2 = Developer.order('salary DESC').collect { |dev| dev.name }
+    received_2 = DeveloperOrderedBySalary.select("id").where("name" => "Jamis").unscope({:where => :name}, :select).collect { |dev| dev.name }
+    assert_equal expected_2, received_2
+
+    expected_3 = Developer.order('salary DESC').collect { |dev| dev.name }
+    received_3 = DeveloperOrderedBySalary.select("id").where("name" => "Jamis").unscope(:select, :where).collect { |dev| dev.name }
+    assert_equal expected_3, received_3
+  end
+
+  def test_unscope_multiple_where_clauses
+    expected = Developer.order('salary DESC').collect { |dev| dev.name }
+    received = DeveloperOrderedBySalary.where(name: 'Jamis').where(id: 1).unscope(where: [:name, :id]).collect { |dev| dev.name }
+    assert_equal expected, received
+  end
+
+  def test_unscope_with_grouping_attributes
+    expected = Developer.order('salary DESC').collect { |dev| dev.name }
+    received = DeveloperOrderedBySalary.group(:name).unscope(:group).collect { |dev| dev.name }
+    assert_equal expected, received
+
+    expected_2 = Developer.order('salary DESC').collect { |dev| dev.name }
+    received_2 = DeveloperOrderedBySalary.group("name").unscope(:group).collect { |dev| dev.name }
+    assert_equal expected_2, received_2
+  end
+
+  def test_unscope_with_limit_in_query
+    expected = Developer.order('salary DESC').collect { |dev| dev.name }
+    received = DeveloperOrderedBySalary.limit(1).unscope(:limit).collect { |dev| dev.name }
+    assert_equal expected, received
+  end
+
+  def test_order_to_unscope_reordering
+    expected = DeveloperOrderedBySalary.all.collect { |dev| [dev.name, dev.id] }
+    received = DeveloperOrderedBySalary.order('salary DESC, name ASC').reverse_order.unscope(:order).collect { |dev| [dev.name, dev.id] }
+    assert_equal expected, received
+  end
+
+  def test_unscope_reverse_order
+    expected = Developer.all.collect { |dev| dev.name }
+    received = Developer.order('salary DESC').reverse_order.unscope(:order).collect { |dev| dev.name }
+    assert_equal expected, received
+  end
+
+  def test_unscope_select
+    expected = Developer.order('salary ASC').collect { |dev| dev.name }
+    received = Developer.order('salary DESC').reverse_order.select(:name => "Jamis").unscope(:select).collect { |dev| dev.name }
+    assert_equal expected, received
+
+    expected_2 = Developer.all.collect { |dev| dev.id }
+    received_2 = Developer.select(:name).unscope(:select).collect { |dev| dev.id }
+    assert_equal expected_2, received_2
+  end
+
+  def test_unscope_offset
+    expected = Developer.all.collect { |dev| dev.name }
+    received = Developer.offset(5).unscope(:offset).collect { |dev| dev.name }
+    assert_equal expected, received
+  end
+
+  def test_unscope_joins_and_select_on_developers_projects
+    expected = Developer.all.collect { |dev| dev.name }
+    received = Developer.joins('JOIN developers_projects ON id = developer_id').select(:id).unscope(:joins, :select).collect { |dev| dev.name }
+    assert_equal expected, received
+  end
+
+  def test_unscope_includes
+    expected = Developer.all.collect { |dev| dev.name }
+    received = Developer.includes(:projects).select(:id).unscope(:includes, :select).collect { |dev| dev.name }
+    assert_equal expected, received
+  end
+
+  def test_unscope_having
+    expected = DeveloperOrderedBySalary.all.collect { |dev| dev.name }
+    received = DeveloperOrderedBySalary.having("name IN ('Jamis', 'David')").unscope(:having).collect { |dev| dev.name }
+    assert_equal expected, received
+  end
+
+  def test_unscope_errors_with_invalid_value
+    assert_raises(ArgumentError) do
+      Developer.includes(:projects).where(name: "Jamis").unscope(:stupidly_incorrect_value)
+    end
+
+    assert_raises(ArgumentError) do
+      Developer.all.unscope(:includes, :select, :some_broken_value)
+    end
+
+    assert_raises(ArgumentError) do
+      Developer.order('name DESC').reverse_order.unscope(:reverse_order)
+    end
+
+    assert_raises(ArgumentError) do
+      Developer.order('name DESC').where(name: "Jamis").unscope()
+    end
+  end
+
+  def test_unscope_errors_with_non_where_hash_keys
+    assert_raises(ArgumentError) do
+      Developer.where(name: "Jamis").limit(4).unscope(limit: 4)
+    end
+
+    assert_raises(ArgumentError) do
+      Developer.where(name: "Jamis").unscope("where" => :name)
+    end
+  end
+
+  def test_unscope_errors_with_non_symbol_or_hash_arguments
+    assert_raises(ArgumentError) do
+      Developer.where(name: "Jamis").limit(3).unscope("limit")
+    end
+
+    assert_raises(ArgumentError) do
+      Developer.select("id").unscope("select")
+    end
+
+    assert_raises(ArgumentError) do 
+      Developer.select("id").unscope(5)
+    end
+  end
+
   def test_order_in_default_scope_should_not_prevail
     expected = Developer.all.merge!(:order => 'salary').to_a.collect { |dev| dev.salary }
     received = DeveloperOrderedBySalary.all.merge!(:order => 'salary').to_a.collect { |dev| dev.salary }

guides/source/active_record_querying.md

@@ -692,6 +692,27 @@ The SQL that would be executed:
 SELECT * FROM posts WHERE id > 10 LIMIT 20
 ```
 
+### `unscope`
+
+The `except` method does not work when the relation is merged. For example:
+
+```ruby
+Post.comments.except(:order)
+```
+
+will still have an order if the order comes from a default scope on Comment. In order to remove all ordering, even from relations which are merged in, use unscope as follows:
+
+```ruby
+Post.order('id DESC').limit(20).unscope(:order) = Post.limit(20)
+Post.order('id DESC').limit(20).unscope(:order, :limit) = Post.all
+```
+
+You can additionally unscope specific where clauses. For example:
+
+```ruby
+Post.where(:id => 10).limit(1).unscope(:where => :id, :limit).order('id DESC') = Post.order('id DESC')
+```
+
 ### `only`
 
 You can also override conditions using the `only` method. For example: