MONGOID-3601 Don't mark embedded objects as persisted when the parent is invalid (#5297)

* MONGOID-3601 what happens if we return nil on valdiation error?

* MONGOID-3061 Don't mark embedded objects get marked as persisted even when the parent is invalid

* clean up

* MONGOID-3601 check for errors instead of persisted

* MONGOID-3061 add document check

Author: neilshweky

lib/mongoid/persistable/creatable.rb

@@ -108,8 +108,10 @@ def prepare_insert(options = {})
               _mongoid_run_child_callbacks(:save) do
                 _mongoid_run_child_callbacks(:create) do
                   result = yield(self)
-                  post_process_insert
-                  post_process_persist(result, options)
+                  if !result.is_a?(Document) || result.errors.empty?
+                    post_process_insert
+                    post_process_persist(result, options)
+                  end
                 end
               end
             end

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

@@ -4719,4 +4719,25 @@ class DNS::Record
       expect(post.company_tags.first.title).to eq("c")
     end
   end
+
+  context "when the parent fails validation" do
+    let(:school) { EmmSchool.new }
+    let(:student) { school.students.new }
+
+    before do
+      student.save
+    end
+
+    it "does not mark the parent as persisted" do
+      expect(school.persisted?).to be false
+    end
+
+    it "does not mark the child as persisted" do
+      expect(student.persisted?).to be false
+    end
+
+    it "does not persist the parent" do
+      expect(School.count).to eq(0)
+    end
+  end
 end

spec/mongoid/association/embedded/embeds_many_models.rb

@@ -188,3 +188,18 @@ class EmmUserTag
   embedded_in :post, class_name: "EmmPost"
 end
 
+class EmmSchool
+  include Mongoid::Document
+
+  embeds_many :students, class_name: "EmmStudent"
+
+  field :name, type: :string
+
+  validates :name, presence: true
+end
+
+class EmmStudent
+  include Mongoid::Document
+
+  embedded_in :school, class_name: "EmmSchool"
+end