diff --git a/app/models/concerns/issuable.rb b/app/models/concerns/issuable.rb
index edf4e9e5d78..16f04305a43 100644
--- a/app/models/concerns/issuable.rb
+++ b/app/models/concerns/issuable.rb
@@ -94,7 +94,6 @@ module Issuable
 
     acts_as_paranoid
 
-    after_save :update_assignee_cache_counts, if: :assignee_id_changed?
     after_save :record_metrics, unless: :imported?
 
     # We want to use optimistic lock for cases when only title or description are involved
diff --git a/app/services/members/authorized_destroy_service.rb b/app/services/members/authorized_destroy_service.rb
index 1711be7211c..a85b9465c84 100644
--- a/app/services/members/authorized_destroy_service.rb
+++ b/app/services/members/authorized_destroy_service.rb
@@ -26,15 +26,22 @@ module Members
 
     def unassign_issues_and_merge_requests(member)
       if member.is_a?(GroupMember)
-        IssuesFinder.new(user, group_id: member.source_id, assignee_id: member.user_id).
-          execute.
-          update_all(assignee_id: nil)
+        issue_ids = IssuesFinder.new(user, group_id: member.source_id, assignee_id: member.user_id).
+          execute.pluck(:id)
+
+        IssueAssignee.destroy_all(issue_id: issue_ids, user_id: member.user_id)
+
         MergeRequestsFinder.new(user, group_id: member.source_id, assignee_id: member.user_id).
           execute.
           update_all(assignee_id: nil)
       else
         project = member.source
-        project.issues.opened.assigned_to(member.user).update_all(assignee_id: nil)
+
+        IssueAssignee.destroy_all(
+          user_id: member.user_id,
+          issue_id: project.issues.opened.assigned_to(member.user).select(:id)
+        )
+
         project.merge_requests.opened.assigned_to(member.user).update_all(assignee_id: nil)
         member.user.update_cache_counts
       end
diff --git a/app/services/system_note_service.rb b/app/services/system_note_service.rb
index 1dee791cfd6..fb1f56c9cc6 100644
--- a/app/services/system_note_service.rb
+++ b/app/services/system_note_service.rb
@@ -84,7 +84,7 @@ module SystemNoteService
         "assigned to #{issue.assignees.map(&:to_reference).to_sentence}"
       end
 
-    NoteSummary.new(issue, project, author, body, action: 'assignee')
+    create_note(NoteSummary.new(issue, project, author, body, action: 'assignee'))
   end
 
   # Called when one or more labels on a Noteable are added and/or removed
diff --git a/db/migrate/20170320171632_create_issue_assignees_table.rb b/db/migrate/20170320171632_create_issue_assignees_table.rb
index 72b70baa8d9..23b8da37b6d 100644
--- a/db/migrate/20170320171632_create_issue_assignees_table.rb
+++ b/db/migrate/20170320171632_create_issue_assignees_table.rb
@@ -26,7 +26,7 @@ class CreateIssueAssigneesTable < ActiveRecord::Migration
   # disable_ddl_transaction!
 
   def up
-    create_table :issue_assignees, id: false do |t|
+    create_table :issue_assignees do |t|
       t.references :user, foreign_key: { on_delete: :cascade }, index: true, null: false
       t.references :issue, foreign_key: { on_delete: :cascade }, null: false
     end
diff --git a/db/schema.rb b/db/schema.rb
index 340d4064c02..7b960f79c1f 100644
--- a/db/schema.rb
+++ b/db/schema.rb
@@ -452,7 +452,7 @@ ActiveRecord::Schema.define(version: 20170502091007) do
 
   add_index "identities", ["user_id"], name: "index_identities_on_user_id", using: :btree
 
-  create_table "issue_assignees", id: false, force: :cascade do |t|
+  create_table "issue_assignees", force: :cascade do |t|
     t.integer "user_id", null: false
     t.integer "issue_id", null: false
   end
diff --git a/lib/github/import.rb b/lib/github/import.rb
index d49761fd6c6..06beb607a3e 100644
--- a/lib/github/import.rb
+++ b/lib/github/import.rb
@@ -245,7 +245,7 @@ module Github
               issue.label_ids    = label_ids(representation.labels)
               issue.milestone_id = milestone_id(representation.milestone)
               issue.author_id    = author_id
-              issue.assignee_id  = user_id(representation.assignee)
+              issue.assignee_ids = [user_id(representation.assignee)]
               issue.created_at   = representation.created_at
               issue.updated_at   = representation.updated_at
               issue.save!(validate: false)
diff --git a/spec/features/dashboard/issuables_counter_spec.rb b/spec/features/dashboard/issuables_counter_spec.rb
index 3d536c5ba40..6f7bf0eba6e 100644
--- a/spec/features/dashboard/issuables_counter_spec.rb
+++ b/spec/features/dashboard/issuables_counter_spec.rb
@@ -19,6 +19,8 @@ describe 'Navigation bar counter', feature: true, caching: true do
 
     issue.assignees = []
 
+    user.update_cache_counts
+
     Timecop.travel(3.minutes.from_now) do
       visit issues_path
 
diff --git a/spec/finders/issues_finder_spec.rb b/spec/finders/issues_finder_spec.rb
index e6bf77aee6a..96151689359 100644
--- a/spec/finders/issues_finder_spec.rb
+++ b/spec/finders/issues_finder_spec.rb
@@ -1,19 +1,19 @@
 require 'spec_helper'
 
 describe IssuesFinder do
-  let(:user) { create(:user) }
-  let(:user2) { create(:user) }
-  let(:project1) { create(:empty_project) }
-  let(:project2) { create(:empty_project) }
-  let(:milestone) { create(:milestone, project: project1) }
-  let(:label) { create(:label, project: project2) }
-  let(:issue1) { create(:issue, author: user, assignees: [user], project: project1, milestone: milestone, title: 'gitlab') }
-  let(:issue2) { create(:issue, author: user, assignees: [user], project: project2, description: 'gitlab') }
-  let(:issue3) { create(:issue, author: user2, assignees: [user2], project: project2, title: 'tanuki', description: 'tanuki') }
+  set(:user) { create(:user) }
+  set(:user2) { create(:user) }
+  set(:project1) { create(:empty_project) }
+  set(:project2) { create(:empty_project) }
+  set(:milestone) { create(:milestone, project: project1) }
+  set(:label) { create(:label, project: project2) }
+  set(:issue1) { create(:issue, author: user, assignees: [user], project: project1, milestone: milestone, title: 'gitlab') }
+  set(:issue2) { create(:issue, author: user, assignees: [user], project: project2, description: 'gitlab') }
+  set(:issue3) { create(:issue, author: user2, assignees: [user2], project: project2, title: 'tanuki', description: 'tanuki') }
 
   describe '#execute' do
-    let(:closed_issue) { create(:issue, author: user2, assignees: [user2], project: project2, state: 'closed') }
-    let!(:label_link) { create(:label_link, label: label, target: issue2) }
+    set(:closed_issue) { create(:issue, author: user2, assignees: [user2], project: project2, state: 'closed') }
+    set(:label_link) { create(:label_link, label: label, target: issue2) }
     let(:search_user) { user }
     let(:params) { {} }
     let(:issues) { described_class.new(search_user, params.reverse_merge(scope: scope, state: 'opened')).execute }
diff --git a/spec/requests/api/v3/issues_spec.rb b/spec/requests/api/v3/issues_spec.rb
index 49191b2eb4e..cc81922697a 100644
--- a/spec/requests/api/v3/issues_spec.rb
+++ b/spec/requests/api/v3/issues_spec.rb
@@ -1157,38 +1157,6 @@ describe API::V3::Issues do
     end
   end
 
-  describe 'PUT /projects/:id/issues/:issue_id to update weight' do
-    it 'updates an issue with no weight' do
-      put v3_api("/projects/#{project.id}/issues/#{issue.id}", user), weight: 5
-
-      expect(response).to have_http_status(200)
-      expect(json_response['weight']).to eq(5)
-    end
-
-    it 'removes a weight from an issue' do
-      weighted_issue = create(:issue, project: project, weight: 2)
-
-      put v3_api("/projects/#{project.id}/issues/#{weighted_issue.id}", user), weight: nil
-
-      expect(response).to have_http_status(200)
-      expect(json_response['weight']).to be_nil
-    end
-
-    it 'returns 400 if weight is less than minimum weight' do
-      put v3_api("/projects/#{project.id}/issues/#{issue.id}", user), weight: -1
-
-      expect(response).to have_http_status(400)
-      expect(json_response['error']).to eq('weight does not have a valid value')
-    end
-
-    it 'returns 400 if weight is more than maximum weight' do
-      put v3_api("/projects/#{project.id}/issues/#{issue.id}", user), weight: 10
-
-      expect(response).to have_http_status(400)
-      expect(json_response['error']).to eq('weight does not have a valid value')
-    end
-  end
-
   describe "DELETE /projects/:id/issues/:issue_id" do
     it "rejects a non member from deleting an issue" do
       delete v3_api("/projects/#{project.id}/issues/#{issue.id}", non_member)
diff --git a/spec/services/system_note_service_spec.rb b/spec/services/system_note_service_spec.rb
index 5f1b82e8355..68816bf36b8 100644
--- a/spec/services/system_note_service_spec.rb
+++ b/spec/services/system_note_service_spec.rb
@@ -164,7 +164,9 @@ describe SystemNoteService, services: true do
     let(:assignee2) { create(:user) }
     let(:assignee3) { create(:user) }
 
-    it_behaves_like 'a system note'
+    it_behaves_like 'a system note' do
+      let(:action) { 'assignee' }
+    end
 
     def build_note(old_assignees, new_assignees)
       issue.assignees = new_assignees
diff --git a/spec/services/users/destroy_service_spec.rb b/spec/services/users/destroy_service_spec.rb
index 8aa900d1a75..de37a61e388 100644
--- a/spec/services/users/destroy_service_spec.rb
+++ b/spec/services/users/destroy_service_spec.rb
@@ -60,7 +60,7 @@ describe Users::DestroyService, services: true do
         it 'migrates the issue so that it is "Unassigned"' do
           migrated_issue = Issue.find_by_id(issue.id)
 
-          expect(migrated_issue.assignees).to be_nil
+          expect(migrated_issue.assignees).to be_empty
         end
       end
     end