MONGOID-5352 assign_attributes is working incorrectly since 7.3.4 (#5274)

* MONGOID-5352 add fix for this issue, other tests failing

* MONGOID-5352 fix two tests, two to go

* MONGOID-5352 fix all tests

* MONGOID-5352 fix some tests

* MONGOID-5352 don't set caches before setting association

* MONGOID-5352 rework solution

* Update lib/mongoid/association/embedded/batchable.rb

* MONGOID-5352 answer comments

* MONGOID-5352 update comment

Author: neilshweky

lib/mongoid/association/embedded/batchable.rb

@@ -85,7 +85,8 @@ def batch_remove(docs, method = :delete)
         def batch_replace(docs)
           if docs.blank?
             if _assigning? && !empty?
-              _base.delayed_atomic_sets.clear
+              _base.delayed_atomic_sets.delete(path)
+              clear_atomic_path_cache
               _base.add_atomic_unset(first)
               target_duplicate = _target.dup
               pre_process_batch_remove(target_duplicate, :delete)
@@ -97,7 +98,8 @@ def batch_replace(docs)
             _base.delayed_atomic_sets.clear unless _assigning?
             docs = normalize_docs(docs).compact
             _target.clear and _unscoped.clear
-            _base.delayed_atomic_unsets.clear
+            _base.delayed_atomic_unsets.delete(path)
+            clear_atomic_path_cache
             inserts = execute_batch_set(docs)
             add_atomic_sets(inserts)
           end
@@ -246,6 +248,17 @@ def path
           end
         end
 
+        # Clear the cache for path and atomic_paths. This method is used when
+        # the path method is used, and the association has not been set on the
+        # document yet, which can cause path and atomic_paths to be calculated
+        # incorrectly later.
+        #
+        # @api private
+        def clear_atomic_path_cache
+          self.path = nil
+          _base.instance_variable_set("@atomic_paths", nil)
+        end
+
         # Set the atomic path.
         #
         # @api private

spec/mongoid/association/embedded/embeds_many/proxy_spec.rb

@@ -4699,4 +4699,24 @@ class DNS::Record
       end
     end
   end
+
+  context "when using assign_attributes with an already populated array" do
+    let(:post) { EmmPost.create! }
+
+    before do
+      post.assign_attributes(company_tags: [{id: BSON::ObjectId.new, title: 'a'}],
+        user_tags: [{id: BSON::ObjectId.new, title: 'b'}])
+      post.save!
+      post.reload
+      post.assign_attributes(company_tags: [{id: BSON::ObjectId.new, title: 'c'}],
+        user_tags: [])
+      post.save!
+      post.reload
+    end
+
+    it "has the correct embedded documents" do
+      expect(post.company_tags.length).to eq(1)
+      expect(post.company_tags.first.title).to eq("c")
+    end
+  end
 end

spec/mongoid/association/embedded/embeds_many_models.rb

@@ -162,3 +162,29 @@ class EmmHatch
   # No :class_name option on this association intentionally.
   embedded_in :tank
 end
+
+class EmmPost
+  include Mongoid::Document
+
+  embeds_many :company_tags, class_name: "EmmCompanyTag"
+  embeds_many :user_tags, class_name: "EmmUserTag"
+end
+
+
+class EmmCompanyTag
+  include Mongoid::Document
+
+  field :title, type: String
+
+  embedded_in :post, class_name: "EmmPost"
+end
+
+
+class EmmUserTag
+  include Mongoid::Document
+
+  field :title, type: String
+
+  embedded_in :post, class_name: "EmmPost"
+end
+