MONGOID-4953 Update the updated_at field when updating a HABTM association (#5219)

* MONGOID-4953 dont update updated_at when modifying _ids field

* MONGOID-4953 update HABTM foreign key on update

* MONGOID-4953 add timestamp tests to document the behavior as described in the PR description

* MONGOID-4953 remove comments

* MONGOID-4953 fix failures

* MONGOID-4953 add a note in documentation

* MONGOID-4953 add timestamp tests after reload

* MONGOID-4953 remove code that updates updated_at

* Update docs and add pending

* MONGOID-4953 add pending

Author: neilshweky

docs/reference/associations.txt

@@ -323,6 +323,12 @@ the ids only in one document using the ``inverse_of: nil`` option:
 A one-sided ``has_and_belongs_to_many`` association is, naturally, only
 usable from the model where it is defined.
 
+.. note::
+
+  Given two models, A and B where A ``has_and_belongs_to_many`` B,
+  when adding a document of type B to the HABTM association on a document of
+  type A, Mongoid will not update the ``updated_at`` field for the document of
+  type A, but will update the ``updated_at`` field for the document of type B.
 
 Querying Referenced Associations
 --------------------------------
@@ -1270,26 +1276,26 @@ to non-existent documents via associations:
 
   class Band
     include Mongoid::Document
-    
+
     has_many :albums
   end
 
   class Album
     include Mongoid::Document
-    
+
     belongs_to :band
   end
-  
+
   band = Band.new
   album = Album.create!(band: band)
-  
+
   # The band is not persisted at this point.
-  
+
   album.reload
-  
+
   album.band_id
   # => BSON::ObjectId('6257699753aefe153121a3d5')
-  
+
   # Band does not exist.
   album.band
   # => nil
@@ -1301,26 +1307,26 @@ add the ``:autosave`` option to the association:
 
   class Band
     include Mongoid::Document
-    
+
     has_many :albums
   end
 
   class Album
     include Mongoid::Document
-    
+
     belongs_to :band, autosave: true
   end
-  
+
   band = Band.new
   album = Album.create!(band: band)
-  
+
   # The band is persisted at this point.
-  
+
   album.reload
-  
+
   album.band_id
   # => BSON::ObjectId('62576b4b53aefe178b65b8e3')
-  
+
   album.band
   # => #<Band _id: 62576b4b53aefe178b65b8e3, >
 
@@ -1339,14 +1345,14 @@ A non-exhaustive list of these operations is as follows:
 - Assignment to the association:
 
   .. code-block:: ruby
-  
+
     # Saves the band and the album.
     band.albums = [Album.new]
 
 - ``push``, ``<<``:
 
   .. code-block:: ruby
-  
+
     band.albums << Album.new
     band.albums.push(Album.new)
 

spec/mongoid/association/referenced/has_and_belongs_to_many_models.rb

@@ -70,6 +70,7 @@ class HabtmmAnimal
 
 class HabtmmSchool
   include Mongoid::Document
+  include Mongoid::Timestamps
 
   has_and_belongs_to_many :students, class_name: 'HabtmmStudent'
 
@@ -80,6 +81,7 @@ class HabtmmSchool
 
 class HabtmmStudent
   include Mongoid::Document
+  include Mongoid::Timestamps
 
   has_and_belongs_to_many :schools, class_name: 'HabtmmSchool'
 

spec/mongoid/association/referenced/has_and_belongs_to_many_spec.rb

@@ -1076,4 +1076,29 @@ class OtherHasManyRightObject; end
       expect(association.inverse_foreign_key_setter).to eq('has_many_left_object_ids=')
     end
   end
+
+  context "when adding an object to the association" do
+    let!(:start_time) { Timecop.freeze(Time.at(Time.now.to_i)) }
+
+    let(:update_time) do
+      Timecop.freeze(Time.at(Time.now.to_i) + 2)
+    end
+
+    after do
+      Timecop.return
+    end
+
+    let!(:school) { HabtmmSchool.create! }
+    let!(:student) { HabtmmStudent.create! }
+
+    before do
+      update_time
+      school.update(students: [student])
+    end
+
+    it "updates the updated at" do
+      pending "MONGOID-4953"
+      expect(school.updated_at).to eq(update_time)
+    end
+  end
 end

spec/mongoid/association/referenced/has_many_models.rb

@@ -42,6 +42,7 @@ class HmmPet
 
 class HmmSchool
   include Mongoid::Document
+  include Mongoid::Timestamps
 
   has_many :students, class_name: 'HmmStudent'
 
@@ -51,8 +52,9 @@ class HmmSchool
 
 class HmmStudent
   include Mongoid::Document
+  include Mongoid::Timestamps
 
-  belongs_to :school, class_name: 'HmmSchool'
+  belongs_to :school, class_name: 'HmmSchool', touch: true
 
   field :name, type: String
   field :grade, type: Integer, default: 3

spec/mongoid/association/referenced/has_many_spec.rb

@@ -1,6 +1,7 @@
 # frozen_string_literal: true
 
 require "spec_helper"
+require_relative './has_many_models'
 
 describe Mongoid::Association::Referenced::HasMany do
 
@@ -1245,4 +1246,28 @@ class OtherBelongingObject; end
       expect(association.create_relation(owner, target)).to be_a(Array)
     end
   end
+
+  context "when adding an object to the association" do
+    let!(:start_time) { Timecop.freeze(Time.at(Time.now.to_i)) }
+
+    let(:update_time) do
+      Timecop.freeze(Time.at(Time.now.to_i) + 2)
+    end
+
+    after do
+      Timecop.return
+    end
+
+    let!(:school) { HmmSchool.create! }
+    let!(:student) { HmmStudent.create! }
+
+    before do
+      update_time
+      student.update(school: school)
+    end
+
+    it "updates the updated_at" do
+      expect(student.updated_at).to eq(update_time)
+    end
+  end
 end