Fix issue #7526. Reload the target if it's stale.

* This has been fixed at master via `365b8b6`, but not at 3-2-stable branch.

* @stale_state should be nil when a model isn't saved. via `0f3901e`.

* set @stale_state to nil when reset the target.

6 files changed, 28 insertions, 6 deletions

diff --git a/activerecord/CHANGELOG.md b/activerecord/CHANGELOG.md
index 519d3f784f..ffc5b95296 100644
--- a/activerecord/CHANGELOG.md
+++ b/activerecord/CHANGELOG.md
@@ -1,5 +1,11 @@
 ## unreleased ##
 
+*   Reload the association target if it's stale. `@stale_state` should be nil
+    when a model isn't saved.
+    Fixes #7526.
+
+    *Larry Lv*
+
 *   Don't read CSV files during execution of `db:fixtures:load`. CSV support for
     fixtures was removed some time ago but the task was still loading them, even
     though later the code was looking for the related yaml file instead.
diff --git a/activerecord/lib/active_record/associations/association.rb b/activerecord/lib/active_record/associations/association.rb
index ab0d888b16..861df46e3c 100644
--- a/activerecord/lib/active_record/associations/association.rb
+++ b/activerecord/lib/active_record/associations/association.rb
@@ -46,6 +46,7 @@ module ActiveRecord
         @loaded = false
         IdentityMap.remove(target) if IdentityMap.enabled? && target
         @target = nil
+        @stale_state = nil
       end
 
       # Reloads the \target and returns +self+ on success.
@@ -134,15 +135,15 @@ module ActiveRecord
       # ActiveRecord::RecordNotFound is rescued within the method, and it is
       # not reraised. The proxy is \reset and +nil+ is the return value.
       def load_target
-        if find_target?
+        if (@stale_state && stale_target?) || find_target?
           begin
             if IdentityMap.enabled? && association_class && association_class.respond_to?(:base_class)
               @target = IdentityMap.get(association_class, owner[reflection.foreign_key])
+            else
+              @target = find_target
             end
           rescue NameError
             nil
-          ensure
-            @target ||= find_target
           end
         end
         loaded! unless loaded?
diff --git a/activerecord/lib/active_record/associations/belongs_to_association.rb b/activerecord/lib/active_record/associations/belongs_to_association.rb
index 97f531d064..52c67df646 100644
--- a/activerecord/lib/active_record/associations/belongs_to_association.rb
+++ b/activerecord/lib/active_record/associations/belongs_to_association.rb
@@ -72,7 +72,7 @@ module ActiveRecord
         end
 
         def stale_state
-          owner[reflection.foreign_key].to_s
+          owner[reflection.foreign_key] && owner[reflection.foreign_key].to_s
         end
     end
   end
diff --git a/activerecord/lib/active_record/associations/belongs_to_polymorphic_association.rb b/activerecord/lib/active_record/associations/belongs_to_polymorphic_association.rb
index 2ee5dbbd70..88ce03a3cd 100644
--- a/activerecord/lib/active_record/associations/belongs_to_polymorphic_association.rb
+++ b/activerecord/lib/active_record/associations/belongs_to_polymorphic_association.rb
@@ -27,7 +27,8 @@ module ActiveRecord
         end
 
         def stale_state
-          [super, owner[reflection.foreign_type].to_s]
+          foreign_key = super
+          foreign_key && [foreign_key.to_s, owner[reflection.foreign_type].to_s]
         end
     end
   end
diff --git a/activerecord/lib/active_record/associations/through_association.rb b/activerecord/lib/active_record/associations/through_association.rb
index fd0e90aaf0..be890e5767 100644
--- a/activerecord/lib/active_record/associations/through_association.rb
+++ b/activerecord/lib/active_record/associations/through_association.rb
@@ -62,7 +62,7 @@ module ActiveRecord
         # properly support stale-checking for nested associations.
         def stale_state
           if through_reflection.macro == :belongs_to
-            owner[through_reflection.foreign_key].to_s
+            owner[through_reflection.foreign_key] && owner[through_reflection.foreign_key].to_s
           end
         end
 
diff --git a/activerecord/test/cases/associations/belongs_to_associations_test.rb b/activerecord/test/cases/associations/belongs_to_associations_test.rb
index f392366c19..c9b26895ae 100644
--- a/activerecord/test/cases/associations/belongs_to_associations_test.rb
+++ b/activerecord/test/cases/associations/belongs_to_associations_test.rb
@@ -14,6 +14,8 @@ require 'models/sponsor'
 require 'models/member'
 require 'models/essay'
 require 'models/toy'
+require 'models/person'
+require 'models/reader'
 
 class BelongsToAssociationsTest < ActiveRecord::TestCase
   fixtures :accounts, :companies, :developers, :projects, :topics,
@@ -716,4 +718,16 @@ class BelongsToAssociationsTest < ActiveRecord::TestCase
 
     assert_equal toy, sponsor.reload.sponsorable
   end
+
+  def test_saving_nested_association
+    post1, post2 = Post.limit(2)
+    person = Person.new(:first_name => 'foo')
+    reader = Reader.new(:post => post1)
+
+    reader.post_id = post2.id
+    person.readers = [reader]
+
+    assert person.save
+    assert_equal reader.post_id, post2.id
+  end
 end