7 files changed, 35 insertions, 7 deletions
diff --git a/activerecord/CHANGELOG.md b/activerecord/CHANGELOG.md
index cd3ca2ab34..97e5d236a8 100644
--- a/activerecord/CHANGELOG.md
+++ b/activerecord/CHANGELOG.md
@@ -1,3 +1,8 @@
+*   Make ActiveRecord::Relation#unscope affect relations it is merged in
+    to.
+
+    *Jon Leighton*
+
 *   Use strings to represent non-string `order_values`.
 
     *Yves Senn*
diff --git a/activerecord/lib/active_record/relation.rb b/activerecord/lib/active_record/relation.rb
index 6e0669a77f..745c6cf349 100644
--- a/activerecord/lib/active_record/relation.rb
+++ b/activerecord/lib/active_record/relation.rb
@@ -7,7 +7,7 @@ module ActiveRecord
 
     MULTI_VALUE_METHODS  = [:includes, :eager_load, :preload, :select, :group,
                             :order, :joins, :where, :having, :bind, :references,
-                            :extending]
+                            :extending, :unscope]
 
     SINGLE_VALUE_METHODS = [:limit, :offset, :lock, :readonly, :from, :reordering,
                             :reverse_order, :distinct, :create_with, :uniq]
diff --git a/activerecord/lib/active_record/relation/query_methods.rb b/activerecord/lib/active_record/relation/query_methods.rb
index b6a7c25b4b..473762011b 100644
--- a/activerecord/lib/active_record/relation/query_methods.rb
+++ b/activerecord/lib/active_record/relation/query_methods.rb
@@ -341,13 +341,19 @@ module ActiveRecord
     #   User.where(name: "John", active: true).unscope(where: :name)
     #       == User.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:
+    # This method is similar to <tt>except</tt>, but unlike
+    # <tt>except</tt>, it persists across merges:
     #
-    #   Post.comments.except(:order)
+    #   User.order('email').merge(User.except(:order))
+    #       == User.order('email')
+    #
+    #   User.order('email').merge(User.unscope(:order))
+    #       == User.all
+    #
+    # This means it can be used in association definitions:
+    #
+    #   has_many :comments, -> { unscope where: :trashed }
     #
-    # 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)
@@ -355,6 +361,7 @@ module ActiveRecord
 
     def unscope!(*args) # :nodoc:
       args.flatten!
+      self.unscope_values += args
 
       args.each do |scope|
         case scope
diff --git a/activerecord/test/cases/associations/has_many_associations_test.rb b/activerecord/test/cases/associations/has_many_associations_test.rb
index b11d27467b..359bcfba5f 100644
--- a/activerecord/test/cases/associations/has_many_associations_test.rb
+++ b/activerecord/test/cases/associations/has_many_associations_test.rb
@@ -1761,4 +1761,13 @@ class HasManyAssociationsTest < ActiveRecord::TestCase
     assert_equal 1, speedometer.minivans.to_a.size, "Only one association should be present:\n#{speedometer.minivans.to_a}"
     assert_equal 1, speedometer.reload.minivans.to_a.size
   end
+
+  test "can unscope the default scope of the associated model" do
+    car = Car.create!
+    bulb1 = Bulb.create! name: "defaulty", car: car
+    bulb2 = Bulb.create! name: "other",    car: car
+
+    assert_equal [bulb1], car.bulbs
+    assert_equal [bulb1, bulb2], car.all_bulbs.sort_by(&:id)
+  end
 end
diff --git a/activerecord/test/cases/relation/mutation_test.rb b/activerecord/test/cases/relation/mutation_test.rb
index a70f979442..7cb2a19bee 100644
--- a/activerecord/test/cases/relation/mutation_test.rb
+++ b/activerecord/test/cases/relation/mutation_test.rb
@@ -20,7 +20,7 @@ module ActiveRecord
       @relation ||= Relation.new FakeKlass.new('posts'), Post.arel_table
     end
 
-    (Relation::MULTI_VALUE_METHODS - [:references, :extending, :order]).each do |method|
+    (Relation::MULTI_VALUE_METHODS - [:references, :extending, :order, :unscope]).each do |method|
       test "##{method}!" do
         assert relation.public_send("#{method}!", :foo).equal?(relation)
         assert_equal [:foo], relation.public_send("#{method}_values")
diff --git a/activerecord/test/cases/scoping/default_scoping_test.rb b/activerecord/test/cases/scoping/default_scoping_test.rb
index 2fbe19ab06..11dd32bfb8 100644
--- a/activerecord/test/cases/scoping/default_scoping_test.rb
+++ b/activerecord/test/cases/scoping/default_scoping_test.rb
@@ -262,6 +262,12 @@ class DefaultScopingTest < ActiveRecord::TestCase
     end
   end
 
+  def test_unscope_merging
+    merged = Developer.where(name: "Jamis").merge(Developer.unscope(:where))
+    assert merged.where_values.empty?
+    assert !merged.where(name: "Jon").where_values.empty?
+  end
+
   def test_order_in_default_scope_should_not_prevail
     expected = Developer.all.merge!(order: 'salary desc').to_a.collect { |dev| dev.salary }
     received = DeveloperOrderedBySalary.all.merge!(order: 'salary').to_a.collect { |dev| dev.salary }
diff --git a/activerecord/test/models/car.rb b/activerecord/test/models/car.rb
index 6d257dbe7e..8f3b70a7c6 100644
--- a/activerecord/test/models/car.rb
+++ b/activerecord/test/models/car.rb
@@ -1,5 +1,6 @@
 class Car < ActiveRecord::Base
   has_many :bulbs
+  has_many :all_bulbs, -> { unscope where: :name }, class_name: "Bulb"
   has_many :funky_bulbs, class_name: 'FunkyBulb', dependent: :destroy
   has_many :foo_bulbs, -> { where(:name => 'foo') }, :class_name => "Bulb"