9 files changed, 62 insertions, 13 deletions
diff --git a/activerecord/CHANGELOG.md b/activerecord/CHANGELOG.md
index 6cc667b754..4d0c1a4178 100644
--- a/activerecord/CHANGELOG.md
+++ b/activerecord/CHANGELOG.md
@@ -1,3 +1,14 @@
+*   Serialize JSON attribute value `nil` as SQL `NULL`, not JSON `null`
+
+    *Trung Duc Tran*
+
+*   Return `true` from `update_attribute` when the value of the attribute
+    to be updated is unchanged.
+
+    Fixes #26593.
+
+    *Prathamesh Sonpatki*
+
 *   Always store errors details information with symbols.
 
     When the association is autosaved we were storing the details with
diff --git a/activerecord/lib/active_record/persistence.rb b/activerecord/lib/active_record/persistence.rb
index 978fb27cab..65248f3a32 100644
--- a/activerecord/lib/active_record/persistence.rb
+++ b/activerecord/lib/active_record/persistence.rb
@@ -252,7 +252,8 @@ module ActiveRecord
       name = name.to_s
       verify_readonly_attribute(name)
       public_send("#{name}=", value)
-      save(validate: false) if changed?
+
+      changed? ? save(validate: false) : true
     end
 
     # Updates the attributes of the model from the passed-in hash and saves the
diff --git a/activerecord/lib/active_record/type/internal/abstract_json.rb b/activerecord/lib/active_record/type/internal/abstract_json.rb
index 513c938088..e19c5a14da 100644
--- a/activerecord/lib/active_record/type/internal/abstract_json.rb
+++ b/activerecord/lib/active_record/type/internal/abstract_json.rb
@@ -17,7 +17,11 @@ module ActiveRecord
         end
 
         def serialize(value)
-          ::ActiveSupport::JSON.encode(value)
+          if value.nil?
+            nil
+          else
+            ::ActiveSupport::JSON.encode(value)
+          end
         end
 
         def accessor
diff --git a/activerecord/test/cases/adapters/mysql2/json_test.rb b/activerecord/test/cases/adapters/mysql2/json_test.rb
index 6b7d259023..630cdb36a4 100644
--- a/activerecord/test/cases/adapters/mysql2/json_test.rb
+++ b/activerecord/test/cases/adapters/mysql2/json_test.rb
@@ -102,6 +102,22 @@ if ActiveRecord::Base.connection.supports_json?
       assert_equal(["v0", { "k1" => "v1" }], x.payload)
     end
 
+    def test_select_nil_json_after_create
+      json = JsonDataType.create(payload: nil)
+      x = JsonDataType.where(payload:nil).first
+      assert_equal(json, x)
+    end
+
+    def test_select_nil_json_after_update
+      json = JsonDataType.create(payload: "foo")
+      x = JsonDataType.where(payload:nil).first
+      assert_equal(nil, x)
+
+      json.update_attributes payload: nil
+      x = JsonDataType.where(payload:nil).first
+      assert_equal(json.reload, x)
+    end
+
     def test_rewrite_array_json_value
       @connection.execute %q|insert into json_data_type (payload) VALUES ('["v0",{"k1":"v1"}]')|
       x = JsonDataType.first
diff --git a/activerecord/test/cases/adapters/postgresql/json_test.rb b/activerecord/test/cases/adapters/postgresql/json_test.rb
index c74f70f251..273b2c1c7b 100644
--- a/activerecord/test/cases/adapters/postgresql/json_test.rb
+++ b/activerecord/test/cases/adapters/postgresql/json_test.rb
@@ -113,6 +113,22 @@ module PostgresqlJSONSharedTestCases
     assert_equal(nil, x.payload)
   end
 
+  def test_select_nil_json_after_create
+    json = JsonDataType.create(payload: nil)
+    x = JsonDataType.where(payload:nil).first
+    assert_equal(json, x)
+  end
+
+  def test_select_nil_json_after_update
+    json = JsonDataType.create(payload: "foo")
+    x = JsonDataType.where(payload:nil).first
+    assert_equal(nil, x)
+
+    json.update_attributes payload: nil
+    x = JsonDataType.where(payload:nil).first
+    assert_equal(json.reload, x)
+  end
+
   def test_select_array_json_value
     @connection.execute %q|insert into json_data_type (payload) VALUES ('["v0",{"k1":"v1"}]')|
     x = JsonDataType.first
diff --git a/activerecord/test/cases/persistence_test.rb b/activerecord/test/cases/persistence_test.rb
index d83360e327..688c3ed2b1 100644
--- a/activerecord/test/cases/persistence_test.rb
+++ b/activerecord/test/cases/persistence_test.rb
@@ -391,14 +391,14 @@ class PersistenceTest < ActiveRecord::TestCase
     end
     topic = klass.create(title: "Another New Topic")
     assert_queries(0) do
-      topic.update_attribute(:title, "Another New Topic")
+      assert topic.update_attribute(:title, "Another New Topic")
     end
   end
 
   def test_update_does_not_run_sql_if_record_has_not_changed
     topic = Topic.create(title: "Another New Topic")
-    assert_queries(0) { topic.update(title: "Another New Topic") }
-    assert_queries(0) { topic.update_attributes(title: "Another New Topic") }
+    assert_queries(0) { assert topic.update(title: "Another New Topic") }
+    assert_queries(0) { assert topic.update_attributes(title: "Another New Topic") }
   end
 
   def test_delete
diff --git a/activesupport/lib/active_support/callbacks.rb b/activesupport/lib/active_support/callbacks.rb
index 3a2c7b0e74..6d39be1c1f 100644
--- a/activesupport/lib/active_support/callbacks.rb
+++ b/activesupport/lib/active_support/callbacks.rb
@@ -738,11 +738,11 @@ module ActiveSupport
         #
         # ===== Notes
         #
-        # +names+ passed to `define_callbacks` must not end with
-        # `!`, `?` or `=`.
+        # +names+ passed to +define_callbacks+ must not end with
+        # <tt>!</tt>, <tt>?</tt> or <tt>=</tt>.
         #
-        # Calling `define_callbacks` multiple times with the same +names+ will
-        # overwrite previous callbacks registered with `set_callback`.
+        # Calling +define_callbacks+ multiple times with the same +names+ will
+        # overwrite previous callbacks registered with +set_callback+.
         def define_callbacks(*names)
           options = names.extract_options!
 
diff --git a/activesupport/lib/active_support/core_ext/load_error.rb b/activesupport/lib/active_support/core_ext/load_error.rb
index 4cb6ffea5e..cd00d1b662 100644
--- a/activesupport/lib/active_support/core_ext/load_error.rb
+++ b/activesupport/lib/active_support/core_ext/load_error.rb
@@ -1,3 +1,4 @@
+require "active_support/deprecation"
 require "active_support/deprecation/proxy_wrappers"
 
 class LoadError
diff --git a/guides/source/testing.md b/guides/source/testing.md
index 8f9246dea2..98847fde18 100644
--- a/guides/source/testing.md
+++ b/guides/source/testing.md
@@ -761,8 +761,8 @@ and also ensuring that the right response body has been generated.
 
 The `get` method kicks off the web request and populates the results into the `@response`. It can accept up to 6 arguments:
 
-* The action of the controller you are requesting.
-  This can be in the form of a string or a route (i.e. `articles_url`).
+* The URI of the controller action you are requesting.
+  This can be in the form of a string or a route helper (e.g. `articles_url`).
 * `params`: option with a hash of request parameters to pass into the action
   (e.g. query string parameters or article variables).
 * `headers`: for setting the headers that will be passed with the request.
@@ -775,13 +775,13 @@ All of these keyword arguments are optional.
 Example: Calling the `:show` action, passing an `id` of 12 as the `params` and setting `HTTP_REFERER` header:
 
 ```ruby
-get :show, params: { id: 12 }, headers: { "HTTP_REFERER" => "http://example.com/home" }
+get article_url, params: { id: 12 }, headers: { "HTTP_REFERER" => "http://example.com/home" }
 ```
 
 Another example: Calling the `:update` action, passing an `id` of 12 as the `params` as an Ajax request.
 
 ```ruby
-patch update_url, params: { id: 12 }, xhr: true
+patch article_url, params: { id: 12 }, xhr: true
 ```
 
 NOTE: If you try running `test_should_create_article` test from `articles_controller_test.rb` it will fail on account of the newly added model level validation and rightly so.