Merge branch '30526-a-be-wiki-activity-Models' into 'master'

#30526 (A) [BE] Wiki Events (models)

See merge request gitlab-org/gitlab!26529

app/models/event.rb

@@ -6,6 +6,7 @@ class Event < ApplicationRecord
   include Presentable
   include DeleteWithLimit
   include CreatedAtFilterable
+  include Gitlab::Utils::StrongMemoize
 
   default_scope { reorder(nil) }
 
@@ -42,7 +43,8 @@ class Event < ApplicationRecord
     note:           Note,
     project:        Project,
     snippet:        Snippet,
-    user:           User
+    user:           User,
+    wiki:           WikiPage::Meta
   ).freeze
 
   RESET_PROJECT_ACTIVITY_INTERVAL = 1.hour
@@ -79,6 +81,7 @@ class Event < ApplicationRecord
   scope :recent, -> { reorder(id: :desc) }
   scope :code_push, -> { where(action: PUSHED) }
   scope :merged, -> { where(action: MERGED) }
+  scope :for_wiki_page, -> { where(target_type: WikiPage::Meta.name) }
 
   scope :with_associations, -> do
     # We're using preload for "push_event_payload" as otherwise the association
@@ -197,6 +200,14 @@ class Event < ApplicationRecord
     created_action? && !target && target_type.nil?
   end
 
+  def created_wiki_page?
+    wiki_page? && action == CREATED
+  end
+
+  def updated_wiki_page?
+    wiki_page? && action == UPDATED
+  end
+
   def created_target?
     created_action? && target
   end
@@ -217,6 +228,10 @@ class Event < ApplicationRecord
     target_type == "MergeRequest"
   end
 
+  def wiki_page?
+    target_type == WikiPage::Meta.name
+  end
+
   def milestone
     target if milestone?
   end
@@ -229,6 +244,14 @@ class Event < ApplicationRecord
     target if merge_request?
   end
 
+  def wiki_page
+    strong_memoize(:wiki_page) do
+      next unless wiki_page?
+
+      ProjectWiki.new(project, author).find_page(target.canonical_slug)
+    end
+  end
+
   def note
     target if note?
   end
@@ -250,6 +273,10 @@ class Event < ApplicationRecord
       'destroyed'
     elsif commented_action?
       "commented on"
+    elsif created_wiki_page?
+      'created'
+    elsif updated_wiki_page?
+      'updated'
     elsif created_project_action?
       created_project_action_name
     else
@@ -362,6 +389,8 @@ class Event < ApplicationRecord
                         :read_snippet
                       elsif milestone?
                         :read_milestone
+                      elsif wiki_page?
+                        :read_wiki
                       end
                     end
   end

app/models/project_wiki.rb

@@ -19,10 +19,11 @@ class ProjectWiki
   DIRECTION_DESC = 'desc'
   DIRECTION_ASC = 'asc'
 
+  attr_reader :project, :user
+
   # Returns a string describing what went wrong after
   # an operation fails.
   attr_reader :error_message
-  attr_reader :project
 
   def initialize(project, user = nil)
     @project = project
@@ -196,9 +197,9 @@ class ProjectWiki
 
   def commit_details(action, message = nil, title = nil)
     commit_message = message.presence || default_message(action, title)
-    git_user = Gitlab::Git::User.from_gitlab(@user)
+    git_user = Gitlab::Git::User.from_gitlab(user)
 
-    Gitlab::Git::Wiki::CommitDetails.new(@user.id,
+    Gitlab::Git::Wiki::CommitDetails.new(user.id,
                                          git_user.username,
                                          git_user.name,
                                          git_user.email,
@@ -206,7 +207,7 @@ class ProjectWiki
   end
 
   def default_message(action, title)
-    "#{@user.username} #{action} page: #{title}"
+    "#{user.username} #{action} page: #{title}"
   end
 
   def update_project_activity

app/models/wiki_page.rb

@@ -21,6 +21,14 @@ class WikiPage
     ActiveModel::Name.new(self, nil, 'wiki')
   end
 
+  def eql?(other)
+    return false unless other.present? && other.is_a?(self.class)
+
+    slug == other.slug && wiki.project == other.wiki.project
+  end
+
+  alias_method :==, :eql?
+
   # Sorts and groups pages by directory.
   #
   # pages - an array of WikiPage objects.
@@ -58,6 +66,7 @@ class WikiPage
 
   # The GitLab ProjectWiki instance.
   attr_reader :wiki
+  delegate :project, to: :wiki
 
   # The raw Gitlab::Git::WikiPage instance.
   attr_reader :page
@@ -70,6 +79,10 @@ class WikiPage
     Gitlab::HookData::WikiPageBuilder.new(self).build
   end
 
+  # Construct a new WikiPage
+  #
+  # @param [ProjectWiki] wiki
+  # @param [Gitlab::Git::WikiPage] page
   def initialize(wiki, page = nil)
     @wiki       = wiki
     @page       = page

app/models/wiki_page/meta.rb

+# frozen_string_literal: true
+
+class WikiPage
+  class Meta < ApplicationRecord
+    include Gitlab::Utils::StrongMemoize
+
+    CanonicalSlugConflictError = Class.new(ActiveRecord::RecordInvalid)
+
+    self.table_name = 'wiki_page_meta'
+
+    belongs_to :project
+
+    has_many :slugs, class_name: 'WikiPage::Slug', foreign_key: 'wiki_page_meta_id', inverse_of: :wiki_page_meta
+    has_many :events, as: :target, dependent: :delete_all # rubocop:disable Cop/ActiveRecordDependent
+
+    validates :title, presence: true
+    validates :project_id, presence: true
+    validate :no_two_metarecords_in_same_project_can_have_same_canonical_slug
+
+    scope :with_canonical_slug, ->(slug) do
+      joins(:slugs).where(wiki_page_slugs: { canonical: true, slug: slug })
+    end
+
+    alias_method :resource_parent, :project
+
+    # Return the (updated) WikiPage::Meta record for a given wiki page
+    #
+    # If none is found, then a new record is created, and its fields are set
+    # to reflect the wiki_page passed.
+    #
+    # @param [String] last_known_slug
+    # @param [WikiPage] wiki_page
+    #
+    # As with all `find_or_create` methods, this one raises errors on
+    # validation issues.
+    def self.find_or_create(last_known_slug, wiki_page)
+      project = wiki_page.wiki.project
+      known_slugs = [last_known_slug, wiki_page.slug].compact.uniq
+      raise 'no slugs!' if known_slugs.empty?
+
+      transaction do
+        found = find_by_canonical_slug(known_slugs, project)
+        meta = found || create(title: wiki_page.title, project_id: project.id)
+
+        meta.update_state(found.nil?, known_slugs, wiki_page)
+
+        # We don't need to run validations here, since find_by_canonical_slug
+        # guarantees that there is no conflict in canonical_slug, and DB
+        # constraints on title and project_id enforce our other invariants
+        # This saves us a query.
+        meta
+      end
+    end
+
+    def self.find_by_canonical_slug(canonical_slug, project)
+      meta, conflict = with_canonical_slug(canonical_slug)
+        .where(project_id: project.id)
+        .limit(2)
+
+      if conflict.present?
+        meta.errors.add(:canonical_slug, 'Duplicate value found')
+        raise CanonicalSlugConflictError.new(meta)
+      end
+
+      meta
+    end
+
+    def canonical_slug
+      strong_memoize(:canonical_slug) { slugs.canonical.first&.slug }
+    end
+
+    def canonical_slug=(slug)
+      return if @canonical_slug == slug
+
+      if persisted?
+        transaction do
+          slugs.canonical.update_all(canonical: false)
+          page_slug = slugs.create_with(canonical: true).find_or_create_by(slug: slug)
+          page_slug.update_columns(canonical: true) unless page_slug.canonical?
+        end
+      else
+        slugs.new(slug: slug, canonical: true)
+      end
+
+      @canonical_slug = slug
+    end
+
+    def update_state(created, known_slugs, wiki_page)
+      update_wiki_page_attributes(wiki_page)
+      insert_slugs(known_slugs, created, wiki_page.slug)
+      self.canonical_slug = wiki_page.slug
+    end
+
+    def update_columns(attrs = {})
+      super(attrs.reverse_merge(updated_at: Time.now.utc))
+    end
+
+    def self.update_all(attrs = {})
+      super(attrs.reverse_merge(updated_at: Time.now.utc))
+    end
+
+    private
+
+    def update_wiki_page_attributes(page)
+      update_columns(title: page.title) unless page.title == title
+    end
+
+    def insert_slugs(strings, is_new, canonical_slug)
+      creation = Time.now.utc
+
+      slug_attrs = strings.map do |slug|
+        {
+          wiki_page_meta_id: id,
+          slug: slug,
+          canonical: (is_new && slug == canonical_slug),
+          created_at: creation,
+          updated_at: creation
+        }
+      end
+      slugs.insert_all(slug_attrs) unless !is_new && slug_attrs.size == 1
+
+      @canonical_slug = canonical_slug if is_new || strings.size == 1
+    end
+
+    def no_two_metarecords_in_same_project_can_have_same_canonical_slug
+      return unless project_id.present? && canonical_slug.present?
+
+      offending = self.class.with_canonical_slug(canonical_slug).where(project_id: project_id)
+      offending = offending.where.not(id: id) if persisted?
+
+      if offending.exists?
+        errors.add(:canonical_slug, 'each page in a wiki must have a distinct canonical slug')
+      end
+    end
+  end
+end

app/models/wiki_page/slug.rb

+# frozen_string_literal: true
+
+class WikiPage
+  class Slug < ApplicationRecord
+    self.table_name = 'wiki_page_slugs'
+
+    belongs_to :wiki_page_meta, class_name: 'WikiPage::Meta', inverse_of: :slugs
+
+    validates :slug, presence: true, uniqueness: { scope: :wiki_page_meta_id }
+    validates :canonical, uniqueness: {
+          scope: :wiki_page_meta_id,
+          if: :canonical?,
+          message: 'Only one slug can be canonical per wiki metadata record'
+    }
+
+    scope :canonical, -> { where(canonical: true) }
+
+    def update_columns(attrs = {})
+      super(attrs.reverse_merge(updated_at: Time.now.utc))
+    end
+
+    def self.update_all(attrs = {})
+      super(attrs.reverse_merge(updated_at: Time.now.utc))
+    end
+  end
+end

app/policies/wiki_page/meta_policy.rb

+# frozen_string_literal: true
+
+class WikiPage::MetaPolicy < BasePolicy
+  delegate { @subject.project }
+end

changelogs/unreleased/30526-a-be-wiki-activity-Models.yml

+---
+title: Adds wiki metadata models
+merge_request: 26529
+author:
+type: added

db/migrate/20200302152516_add_wiki_slug.rb

+# frozen_string_literal: true
+
+class AddWikiSlug < ActiveRecord::Migration[6.0]
+  DOWNTIME = false
+
+  def change
+    create_table :wiki_page_meta, id: :serial do |t|
+      t.references :project, index: true, foreign_key: { on_delete: :cascade }, null: false
+      t.timestamps_with_timezone null: false
+      t.string :title, null: false, limit: 255
+    end
+
+    create_table :wiki_page_slugs, id: :serial do |t|
+      t.boolean :canonical, default: false, null: false
+      t.references :wiki_page_meta, index: true, foreign_key: { on_delete: :cascade }, null: false
+      t.timestamps_with_timezone null: false
+      t.string :slug, null: false, limit: 2048
+      t.index [:slug, :wiki_page_meta_id], unique: true
+      t.index [:wiki_page_meta_id], name: 'one_canonical_wiki_page_slug_per_metadata', unique: true, where: "(canonical = true)"
+    end
+  end
+end

db/schema.rb

@@ -4668,6 +4668,25 @@ ActiveRecord::Schema.define(version: 2020_03_13_123934) do
     t.index ["type"], name: "index_web_hooks_on_type"
   end
 
+  create_table "wiki_page_meta", id: :serial, force: :cascade do |t|
+    t.bigint "project_id", null: false
+    t.datetime_with_timezone "created_at", null: false
+    t.datetime_with_timezone "updated_at", null: false
+    t.string "title", limit: 255, null: false
+    t.index ["project_id"], name: "index_wiki_page_meta_on_project_id"
+  end
+
+  create_table "wiki_page_slugs", id: :serial, force: :cascade do |t|
+    t.boolean "canonical", default: false, null: false
+    t.bigint "wiki_page_meta_id", null: false
+    t.datetime_with_timezone "created_at", null: false
+    t.datetime_with_timezone "updated_at", null: false
+    t.string "slug", limit: 2048, null: false
+    t.index ["slug", "wiki_page_meta_id"], name: "index_wiki_page_slugs_on_slug_and_wiki_page_meta_id", unique: true
+    t.index ["wiki_page_meta_id"], name: "index_wiki_page_slugs_on_wiki_page_meta_id"
+    t.index ["wiki_page_meta_id"], name: "one_canonical_wiki_page_slug_per_metadata", unique: true, where: "(canonical = true)"
+  end
+
   create_table "x509_certificates", force: :cascade do |t|
     t.datetime_with_timezone "created_at", null: false
     t.datetime_with_timezone "updated_at", null: false
@@ -5212,6 +5231,8 @@ ActiveRecord::Schema.define(version: 2020_03_13_123934) do
   add_foreign_key "vulnerability_scanners", "projects", on_delete: :cascade
   add_foreign_key "web_hook_logs", "web_hooks", on_delete: :cascade
   add_foreign_key "web_hooks", "projects", name: "fk_0c8ca6d9d1", on_delete: :cascade
+  add_foreign_key "wiki_page_meta", "projects", on_delete: :cascade
+  add_foreign_key "wiki_page_slugs", "wiki_page_meta", column: "wiki_page_meta_id", on_delete: :cascade
   add_foreign_key "x509_certificates", "x509_issuers", on_delete: :cascade
   add_foreign_key "x509_commit_signatures", "projects", on_delete: :cascade
   add_foreign_key "x509_commit_signatures", "x509_certificates", on_delete: :cascade

lib/gitlab/hook_data/wiki_page_builder.rb

@@ -12,6 +12,10 @@ module Gitlab
             'content' => absolute_image_urls(wiki_page.content)
           )
       end
+
+      def uploads_prefix
+        ''
+      end
     end
   end
 end

spec/factories/events.rb

@@ -22,6 +22,16 @@ FactoryBot.define do
       action { Event::CLOSED }
       target factory: :closed_issue
     end
+
+    factory :wiki_page_event do
+      action { Event::CREATED }
+
+      transient do
+        wiki_page { create(:wiki_page, project: project) }
+      end
+
+      target { create(:wiki_page_meta, :for_wiki_page, wiki_page: wiki_page) }
+    end
   end
 
   factory :push_event, class: 'PushEvent' do

spec/factories/wiki_pages.rb

@@ -5,17 +5,22 @@ require 'ostruct'
 FactoryBot.define do
   factory :wiki_page do
     transient do
+      title { generate(:wiki_page_title) }
+      content { 'Content for wiki page' }
+      format { 'markdown' }
+      project { create(:project) }
       attrs do
         {
-          title: 'Title.with.dot',
-          content: 'Content for wiki page',
-          format: 'markdown'
+          title: title,
+          content: content,
+          format: format
         }
       end
     end
 
     page { OpenStruct.new(url_path: 'some-name') }
-    association :wiki, factory: :project_wiki, strategy: :build
+    wiki { build(:project_wiki, project: project) }
+
     initialize_with { new(wiki, page) }
 
     before(:create) do |page, evaluator|
@@ -25,5 +30,48 @@ FactoryBot.define do
     to_create do |page|
       page.create
     end
+
+    trait :with_real_page do
+      project { create(:project, :repository) }
+
+      page do
+        wiki.create_page(title, content)
+        page_title, page_dir = wiki.page_title_and_dir(title)
+        wiki.wiki.page(title: page_title, dir: page_dir, version: nil)
+      end
+    end
   end
+
+  factory :wiki_page_meta, class: 'WikiPage::Meta' do
+    title { generate(:wiki_page_title) }
+    project { create(:project) }
+
+    trait :for_wiki_page do
+      transient do
+        wiki_page { create(:wiki_page, project: project) }
+      end
+
+      project { @overrides[:wiki_page]&.project || create(:project) }
+      title { wiki_page.title }
+
+      initialize_with do
+        raise 'Metadata only available for valid pages' unless wiki_page.valid?
+
+        WikiPage::Meta.find_or_create(wiki_page.slug, wiki_page)
+      end
+    end
+  end
+
+  factory :wiki_page_slug, class: 'WikiPage::Slug' do
+    wiki_page_meta { create(:wiki_page_meta) }
+    slug { generate(:sluggified_title) }
+    canonical { false }
+
+    trait :canonical do
+      canonical { true }
+    end
+  end
+
+  sequence(:wiki_page_title) { |n| "Page #{n}" }
+  sequence(:sluggified_title) { |n| "slug-#{n}" }
 end

spec/lib/gitlab/import_export/safe_model_attributes.yml

@@ -40,6 +40,14 @@ Event:
 - updated_at
 - action
 - author_id
+WikiPage::Meta:
+- id
+- title
+- project_id
+WikiPage::Slug:
+- id
+- wiki_page_meta_id
+- slug
 PushEventPayload:
 - commit_count
 - action

spec/models/event_spec.rb

@@ -99,6 +99,39 @@ describe Event do
     end
   end
 
+  describe '#target_title' do
+    let_it_be(:project) { create(:project) }
+
+    let(:author) { project.owner }
+    let(:target) { nil }
+
+    let(:event) do
+      described_class.new(project: project,
+                          target: target,
+                          author_id: author.id)
+    end
+
+    context 'for an issue' do
+      let(:title) { generate(:title) }
+      let(:issue) { create(:issue, title: title, project: project) }
+      let(:target) { issue }
+
+      it 'delegates to issue title' do
+        expect(event.target_title).to eq(title)
+      end
+    end
+
+    context 'for a wiki page' do
+      let(:title) { generate(:wiki_page_title) }
+      let(:wiki_page) { create(:wiki_page, title: title, project: project) }
+      let(:event) { create(:wiki_page_event, project: project, wiki_page: wiki_page) }
+
+      it 'delegates to wiki page title' do
+        expect(event.target_title).to eq(wiki_page.title)
+      end
+    end
+  end
+
   describe '#membership_changed?' do
     context "created" do
       subject { build(:event, :created).membership_changed? }
@@ -148,13 +181,16 @@ describe Event do
   end
 
   describe '#visible_to_user?' do
-    let(:project) { create(:project, :public) }
-    let(:non_member) { create(:user) }
-    let(:member) { create(:user) }
-    let(:guest) { create(:user) }
-    let(:author) { create(:author) }
-    let(:assignee) { create(:user) }
-    let(:admin) { create(:admin) }
+    let_it_be(:non_member) { create(:user) }
+    let_it_be(:member) { create(:user) }
+    let_it_be(:guest) { create(:user) }
+    let_it_be(:author) { create(:author) }
+    let_it_be(:assignee) { create(:user) }
+    let_it_be(:admin) { create(:admin) }
+    let_it_be(:public_project) { create(:project, :public) }
+    let_it_be(:private_project) { create(:project, :private) }
+
+    let(:project) { public_project }
     let(:issue) { create(:issue, project: project, author: author, assignees: [assignee]) }
     let(:confidential_issue) { create(:issue, :confidential, project: project, author: author, assignees: [assignee]) }
     let(:project_snippet) { create(:project_snippet, :public, project: project, author: author) }
@@ -165,36 +201,77 @@ describe Event do
     let(:note_on_project_snippet) { create(:note_on_project_snippet, author: author, noteable: project_snippet, project: project) }
     let(:note_on_personal_snippet) { create(:note_on_personal_snippet, author: author, noteable: personal_snippet, project: nil) }
     let(:milestone_on_project) { create(:milestone, project: project) }
-    let(:event) { described_class.new(project: project, target: target, author_id: author.id) }
+    let(:event) do
+      described_class.new(project: project,
+                          target: target,
+                          author_id: author.id)
+    end
 
     before do
       project.add_developer(member)
       project.add_guest(guest)
     end
 
+    def visible_to_all
+      {
+        logged_out: true,
+        non_member: true,
+        guest: true,
+        member: true,
+        admin: true
+      }
+    end
+
+    def visible_to_none
+      visible_to_all.transform_values { |_| false }
+    end
+
+    def visible_to_none_except(*roles)
+      visible_to_none.merge(roles.map { |role| [role, true] }.to_h)
+    end
+
+    def visible_to_all_except(*roles)
+      visible_to_all.merge(roles.map { |role| [role, false] }.to_h)
+    end
+
+    shared_examples 'visibility examples' do
+      it 'has the correct visibility' do
+        expect({
+          logged_out: event.visible_to_user?(nil),
+          non_member: event.visible_to_user?(non_member),
+          guest: event.visible_to_user?(guest),
+          member: event.visible_to_user?(member),
+          admin: event.visible_to_user?(admin)
+        }).to match(visibility)
+      end
+    end
+
+    shared_examples 'visible to assignee' do |visible|
+      it { expect(event.visible_to_user?(assignee)).to eq(visible) }
+    end
+
+    shared_examples 'visible to author' do |visible|
+      it { expect(event.visible_to_user?(author)).to eq(visible) }
+    end
+
+    shared_examples 'visible to assignee and author' do |visible|
+      include_examples 'visible to assignee', visible
+      include_examples 'visible to author', visible
+    end
+
     context 'commit note event' do
       let(:project) { create(:project, :public, :repository) }
       let(:target) { note_on_commit }
 
-      it do
-        aggregate_failures do
-          expect(event.visible_to_user?(non_member)).to eq true
-          expect(event.visible_to_user?(member)).to eq true
-          expect(event.visible_to_user?(guest)).to eq true
-          expect(event.visible_to_user?(admin)).to eq true
-        end
+      include_examples 'visibility examples' do
+        let(:visibility) { visible_to_all }
       end
 
       context 'private project' do
         let(:project) { create(:project, :private, :repository) }
 
-        it do
-          aggregate_failures do
-            expect(event.visible_to_user?(non_member)).to eq false
-            expect(event.visible_to_user?(member)).to eq true
-            expect(event.visible_to_user?(guest)).to eq false
-            expect(event.visible_to_user?(admin)).to eq true
-          end
+        include_examples 'visibility examples' do
+          let(:visibility) { visible_to_none_except(:member, :admin) }
         end
       end
     end
@@ -203,27 +280,19 @@ describe Event do
       context 'for non confidential issues' do
         let(:target) { issue }
 
-        it do
-          expect(event.visible_to_user?(non_member)).to eq true
-          expect(event.visible_to_user?(author)).to eq true
-          expect(event.visible_to_user?(assignee)).to eq true
-          expect(event.visible_to_user?(member)).to eq true
-          expect(event.visible_to_user?(guest)).to eq true
-          expect(event.visible_to_user?(admin)).to eq true
+        include_examples 'visibility examples' do
+          let(:visibility) { visible_to_all }
         end
+        include_examples 'visible to assignee and author', true
       end
 
       context 'for confidential issues' do
         let(:target) { confidential_issue }
 
-        it do
-          expect(event.visible_to_user?(non_member)).to eq false
-          expect(event.visible_to_user?(author)).to eq true
-          expect(event.visible_to_user?(assignee)).to eq true
-          expect(event.visible_to_user?(member)).to eq true
-          expect(event.visible_to_user?(guest)).to eq false
-          expect(event.visible_to_user?(admin)).to eq true
+        include_examples 'visibility examples' do
+          let(:visibility) { visible_to_none_except(:member, :admin) }
         end
+        include_examples 'visible to assignee and author', true
       end
     end
 
@@ -231,105 +300,99 @@ describe Event do
       context 'on non confidential issues' do
         let(:target) { note_on_issue }
 
-        it do
-          expect(event.visible_to_user?(non_member)).to eq true
-          expect(event.visible_to_user?(author)).to eq true
-          expect(event.visible_to_user?(assignee)).to eq true
-          expect(event.visible_to_user?(member)).to eq true
-          expect(event.visible_to_user?(guest)).to eq true
-          expect(event.visible_to_user?(admin)).to eq true
+        include_examples 'visibility examples' do
+          let(:visibility) { visible_to_all }
         end
+        include_examples 'visible to assignee and author', true
       end
 
       context 'on confidential issues' do
         let(:target) { note_on_confidential_issue }
 
-        it do
-          expect(event.visible_to_user?(non_member)).to eq false
-          expect(event.visible_to_user?(author)).to eq true
-          expect(event.visible_to_user?(assignee)).to eq true
-          expect(event.visible_to_user?(member)).to eq true
-          expect(event.visible_to_user?(guest)).to eq false
-          expect(event.visible_to_user?(admin)).to eq true
+        include_examples 'visibility examples' do
+          let(:visibility) { visible_to_none_except(:member, :admin) }
         end
+        include_examples 'visible to assignee and author', true
       end
 
       context 'private project' do
-        let(:project) { create(:project, :private) }
+        let(:project) { private_project }
         let(:target) { note_on_issue }
 
-        it do
-          expect(event.visible_to_user?(non_member)).to eq false
-          expect(event.visible_to_user?(author)).to eq false
-          expect(event.visible_to_user?(assignee)).to eq false
-          expect(event.visible_to_user?(member)).to eq true
-          expect(event.visible_to_user?(guest)).to eq true
-          expect(event.visible_to_user?(admin)).to eq true
+        include_examples 'visibility examples' do
+          let(:visibility) { visible_to_none_except(:guest, :member, :admin) }
         end
+
+        include_examples 'visible to assignee and author', false
       end
     end
 
     context 'merge request diff note event' do
-      let(:project) { create(:project, :public) }
       let(:merge_request) { create(:merge_request, source_project: project, author: author, assignees: [assignee]) }
       let(:note_on_merge_request) { create(:legacy_diff_note_on_merge_request, noteable: merge_request, project: project) }
       let(:target) { note_on_merge_request }
 
-      it do
-        expect(event.visible_to_user?(non_member)).to eq true
-        expect(event.visible_to_user?(author)).to eq true
-        expect(event.visible_to_user?(assignee)).to eq true
-        expect(event.visible_to_user?(member)).to eq true
-        expect(event.visible_to_user?(guest)).to eq true
-        expect(event.visible_to_user?(admin)).to eq true
+      context 'public project' do
+        let(:project) { public_project }
+
+        include_examples 'visibility examples' do
+          let(:visibility) { visible_to_all }
+        end
+
+        include_examples 'visible to assignee', true
       end
 
       context 'private project' do
-        let(:project) { create(:project, :private) }
+        let(:project) { private_project }
 
-        it do
-          expect(event.visible_to_user?(non_member)).to eq false
-          expect(event.visible_to_user?(author)).to eq false
-          expect(event.visible_to_user?(assignee)).to eq false
-          expect(event.visible_to_user?(member)).to eq true
-          expect(event.visible_to_user?(guest)).to eq false
-          expect(event.visible_to_user?(admin)).to eq true
+        include_examples 'visibility examples' do
+          let(:visibility) { visible_to_none_except(:member, :admin) }
         end
+
+        include_examples 'visible to assignee', false
       end
     end
 
     context 'milestone event' do
       let(:target) { milestone_on_project }
 
-      it do
-        expect(event.visible_to_user?(nil)).to be_truthy
-        expect(event.visible_to_user?(non_member)).to be_truthy
-        expect(event.visible_to_user?(member)).to be_truthy
-        expect(event.visible_to_user?(guest)).to be_truthy
-        expect(event.visible_to_user?(admin)).to be_truthy
+      include_examples 'visibility examples' do
+        let(:visibility) { visible_to_all }
       end
 
       context 'on public project with private issue tracker and merge requests' do
         let(:project) { create(:project, :public, :issues_private, :merge_requests_private) }
 
-        it do
-          expect(event.visible_to_user?(nil)).to be_falsy
-          expect(event.visible_to_user?(non_member)).to be_falsy
-          expect(event.visible_to_user?(member)).to be_truthy
-          expect(event.visible_to_user?(guest)).to be_truthy
-          expect(event.visible_to_user?(admin)).to be_truthy
+        include_examples 'visibility examples' do
+          let(:visibility) { visible_to_all_except(:logged_out, :non_member) }
         end
       end
 
       context 'on private project' do
         let(:project) { create(:project, :private) }
 
-        it do
-          expect(event.visible_to_user?(nil)).to be_falsy
-          expect(event.visible_to_user?(non_member)).to be_falsy
-          expect(event.visible_to_user?(member)).to be_truthy
-          expect(event.visible_to_user?(guest)).to be_truthy
-          expect(event.visible_to_user?(admin)).to be_truthy
+        include_examples 'visibility examples' do
+          let(:visibility) { visible_to_all_except(:logged_out, :non_member) }
+        end
+      end
+    end
+
+    context 'wiki-page event', :aggregate_failures do
+      let(:event) { create(:wiki_page_event, project: project) }
+
+      context 'on private project', :aggregate_failures do
+        let(:project) { create(:project, :wiki_repo) }
+
+        include_examples 'visibility examples' do
+          let(:visibility) { visible_to_all_except(:logged_out, :non_member) }
+        end
+      end
+
+      context 'wiki-page event on public project', :aggregate_failures do
+        let(:project) { create(:project, :public, :wiki_repo) }
+
+        include_examples 'visibility examples' do
+          let(:visibility) { visible_to_all }
         end
       end
     end
@@ -337,79 +400,98 @@ describe Event do
     context 'project snippet note event' do
       let(:target) { note_on_project_snippet }
 
-      it do
-        expect(event.visible_to_user?(nil)).to be_truthy
-        expect(event.visible_to_user?(non_member)).to be_truthy
-        expect(event.visible_to_user?(author)).to be_truthy
-        expect(event.visible_to_user?(member)).to be_truthy
-        expect(event.visible_to_user?(guest)).to be_truthy
-        expect(event.visible_to_user?(admin)).to be_truthy
+      include_examples 'visibility examples' do
+        let(:visibility) { visible_to_all }
       end
 
       context 'on public project with private snippets' do
         let(:project) { create(:project, :public, :snippets_private) }
 
-        it do
-          expect(event.visible_to_user?(nil)).to be_falsy
-          expect(event.visible_to_user?(non_member)).to be_falsy
-
-          # Normally, we'd expect the author of a comment to be able to view it.
-          # However, this doesn't seem to be the case for comments on snippets.
-          expect(event.visible_to_user?(author)).to be_falsy
-
-          expect(event.visible_to_user?(member)).to be_truthy
-          expect(event.visible_to_user?(guest)).to be_truthy
-          expect(event.visible_to_user?(admin)).to be_truthy
+        include_examples 'visibility examples' do
+          let(:visibility) { visible_to_none_except(:guest, :member, :admin) }
         end
+        # Normally, we'd expect the author of a comment to be able to view it.
+        # However, this doesn't seem to be the case for comments on snippets.
+        include_examples 'visible to author', false
       end
 
       context 'on private project' do
         let(:project) { create(:project, :private) }
 
-        it do
-          expect(event.visible_to_user?(nil)).to be_falsy
-          expect(event.visible_to_user?(non_member)).to be_falsy
-
-          # Normally, we'd expect the author of a comment to be able to view it.
-          # However, this doesn't seem to be the case for comments on snippets.
-          expect(event.visible_to_user?(author)).to be_falsy
-
-          expect(event.visible_to_user?(member)).to be_truthy
-          expect(event.visible_to_user?(guest)).to be_truthy
-          expect(event.visible_to_user?(admin)).to be_truthy
+        include_examples 'visibility examples' do
+          let(:visibility) { visible_to_none_except(:guest, :member, :admin) }
         end
+        # Normally, we'd expect the author of a comment to be able to view it.
+        # However, this doesn't seem to be the case for comments on snippets.
+        include_examples 'visible to author', false
       end
     end
 
     context 'personal snippet note event' do
       let(:target) { note_on_personal_snippet }
 
-      it do
-        expect(event.visible_to_user?(nil)).to be_truthy
-        expect(event.visible_to_user?(non_member)).to be_truthy
-        expect(event.visible_to_user?(author)).to be_truthy
-        expect(event.visible_to_user?(admin)).to be_truthy
+      include_examples 'visibility examples' do
+        let(:visibility) { visible_to_all }
       end
+      include_examples 'visible to author', true
 
       context 'on internal snippet' do
         let(:personal_snippet) { create(:personal_snippet, :internal, author: author) }
 
-        it do
-          expect(event.visible_to_user?(nil)).to be_falsy
-          expect(event.visible_to_user?(non_member)).to be_truthy
-          expect(event.visible_to_user?(author)).to be_truthy
-          expect(event.visible_to_user?(admin)).to be_truthy
+        include_examples 'visibility examples' do
+          let(:visibility) { visible_to_all_except(:logged_out) }
         end
       end
 
       context 'on private snippet' do
         let(:personal_snippet) { create(:personal_snippet, :private, author: author) }
 
-        it do
-          expect(event.visible_to_user?(nil)).to be_falsy
-          expect(event.visible_to_user?(non_member)).to be_falsy
-          expect(event.visible_to_user?(author)).to be_truthy
-          expect(event.visible_to_user?(admin)).to be_truthy
+        include_examples 'visibility examples' do
+          let(:visibility) { visible_to_none_except(:admin) }
+        end
+        include_examples 'visible to author', true
+      end
+    end
+  end
+
+  describe '.for_wiki_page' do
+    let_it_be(:events) do
+      [
+        create(:closed_issue_event),
+        create(:wiki_page_event),
+        create(:closed_issue_event),
+        create(:event, :created),
+        create(:wiki_page_event)
+      ]
+    end
+
+    it 'only contains the wiki page events' do
+      wiki_events = events.select(&:wiki_page?)
+
+      expect(described_class.for_wiki_page).to match_array(wiki_events)
+    end
+  end
+
+  describe '#wiki_page and #wiki_page?' do
+    let_it_be(:project) { create(:project, :repository) }
+
+    context 'for a wiki page event' do
+      let(:wiki_page) do
+        create(:wiki_page, :with_real_page, project: project)
+      end
+
+      subject(:event) { create(:wiki_page_event, project: project, wiki_page: wiki_page) }
+
+      it { is_expected.to have_attributes(wiki_page?: be_truthy, wiki_page: wiki_page) }
+    end
+
+    [:issue, :user, :merge_request, :snippet, :milestone, nil].each do |kind|
+      context "for a #{kind} event" do
+        it 'is nil' do
+          target = create(kind) if kind
+          event = create(:event, project: project, target: target)
+
+          expect(event).to have_attributes(wiki_page: be_nil, wiki_page?: be_falsy)
         end
       end
     end

spec/models/wiki_page/meta_spec.rb

+# frozen_string_literal: true
+
+require 'spec_helper'
+
+describe WikiPage::Meta do
+  let_it_be(:project) { create(:project) }
+  let_it_be(:other_project) { create(:project) }
+
+  describe 'Associations' do
+    it { is_expected.to belong_to(:project) }
+    it { is_expected.to have_many(:slugs) }
+    it { is_expected.to have_many(:events) }
+
+    it 'can find slugs' do
+      meta = create(:wiki_page_meta)
+      slugs = create_list(:wiki_page_slug, 3, wiki_page_meta: meta)
+
+      expect(meta.slugs).to match_array(slugs)
+    end
+  end
+
+  describe 'Validations' do
+    subject do
+      described_class.new(title: 'some title', project: project)
+    end
+
+    it { is_expected.to validate_presence_of(:project_id) }
+    it { is_expected.to validate_presence_of(:title) }
+
+    it 'is forbidden to add extremely long titles' do
+      expect do
+        create(:wiki_page_meta, project: project, title: FFaker::Lorem.characters(300))
+      end.to raise_error(ActiveRecord::ValueTooLong)
+    end
+
+    it 'is forbidden to have two records for the same project with the same canonical_slug' do
+      the_slug = generate(:sluggified_title)
+      create(:wiki_page_meta, canonical_slug: the_slug, project: project)
+
+      in_violation = build(:wiki_page_meta, canonical_slug: the_slug, project: project)
+
+      expect(in_violation).not_to be_valid
+    end
+  end
+
+  describe '#canonical_slug' do
+    subject { described_class.find(meta.id) }
+
+    let_it_be(:meta) do
+      described_class.create(title: generate(:wiki_page_title), project: project)
+    end
+
+    context 'there are no slugs' do
+      it { is_expected.to have_attributes(canonical_slug: be_nil) }
+    end
+
+    it 'can be set on initialization' do
+      meta = create(:wiki_page_meta, canonical_slug: 'foo')
+
+      expect(meta.canonical_slug).to eq('foo')
+    end
+
+    context 'we have some non-canonical slugs' do
+      before do
+        create_list(:wiki_page_slug, 2, wiki_page_meta: subject)
+      end
+
+      it { is_expected.to have_attributes(canonical_slug: be_nil) }
+
+      it 'issues at most one query' do
+        expect { subject.canonical_slug }.not_to exceed_query_limit(1)
+      end
+
+      it 'issues no queries if we already know the slug' do
+        subject.canonical_slug
+
+        expect { subject.canonical_slug }.not_to exceed_query_limit(0)
+      end
+    end
+
+    context 'we have a canonical slug' do
+      before do
+        create_list(:wiki_page_slug, 2, wiki_page_meta: subject)
+      end
+
+      it 'has the correct value' do
+        slug = create(:wiki_page_slug, :canonical, wiki_page_meta: subject)
+
+        is_expected.to have_attributes(canonical_slug: slug.slug)
+      end
+    end
+
+    describe 'canonical_slug=' do
+      shared_examples 'canonical_slug setting examples' do
+        # Constant overhead of two queries for the transaction
+        let(:upper_query_limit) { query_limit + 2 }
+        let(:lower_query_limit) { [upper_query_limit - 1, 0].max}
+        let(:other_slug) { generate(:sluggified_title) }
+
+        it 'changes it to the correct value' do
+          subject.canonical_slug = slug
+
+          expect(subject).to have_attributes(canonical_slug: slug)
+        end
+
+        it 'ensures the slug is in the db' do
+          subject.canonical_slug = slug
+
+          expect(subject.slugs.canonical.where(slug: slug)).to exist
+        end
+
+        it 'issues at most N queries' do
+          expect { subject.canonical_slug = slug }.not_to exceed_query_limit(upper_query_limit)
+        end
+
+        it 'issues fewer queries if we already know the current slug' do
+          subject.canonical_slug = other_slug
+
+          expect { subject.canonical_slug = slug }.not_to exceed_query_limit(lower_query_limit)
+        end
+      end
+
+      context 'the slug is not known to us' do
+        let(:slug) { generate(:sluggified_title) }
+        let(:query_limit) { 8 }
+
+        include_examples 'canonical_slug setting examples'
+      end
+
+      context 'the slug is already in the DB (but not canonical)' do
+        let_it_be(:slug_record) { create(:wiki_page_slug, wiki_page_meta: meta) }
+        let(:slug) { slug_record.slug }
+        let(:query_limit) { 4 }
+
+        include_examples 'canonical_slug setting examples'
+      end
+
+      context 'the slug is already in the DB (and canonical)' do
+        let_it_be(:slug_record) { create(:wiki_page_slug, :canonical, wiki_page_meta: meta) }
+        let(:slug) { slug_record.slug }
+        let(:query_limit) { 4 }
+
+        include_examples 'canonical_slug setting examples'
+      end
+
+      context 'the slug is up to date and in the DB' do
+        let(:slug) { generate(:sluggified_title) }
+
+        before do
+          subject.canonical_slug = slug
+        end
+
+        include_examples 'canonical_slug setting examples' do
+          let(:other_slug) { slug }
+          let(:upper_query_limit) { 0 }
+        end
+      end
+    end
+  end
+
+  describe '.find_or_create' do
+    let(:old_title)       { generate(:wiki_page_title) }
+    let(:last_known_slug) { generate(:sluggified_title) }
+    let(:current_slug) { wiki_page.slug }
+    let(:title)        { wiki_page.title }
+    let(:wiki_page) { create(:wiki_page, project: project) }
+
+    def find_record
+      described_class.find_or_create(last_known_slug, wiki_page)
+    end
+
+    def create_previous_version(title = old_title, slug = last_known_slug)
+      create(:wiki_page_meta, title: title, project: project, canonical_slug: slug)
+    end
+
+    def create_context
+      # Ensure that we behave nicely with respect to other projects
+      # We have:
+      #  - page in other project with same canonical_slug
+      create(:wiki_page_meta, project: other_project, canonical_slug: wiki_page.slug)
+
+      #  - page in same project with different canonical_slug, but with
+      #    an old slug that = canonical_slug
+      different_slug = generate(:sluggified_title)
+      create(:wiki_page_meta, project: project, canonical_slug: different_slug)
+        .slugs.create(slug: wiki_page.slug)
+    end
+
+    shared_examples 'metadata examples' do
+      it 'establishes the correct state', :aggregate_failures do
+        create_context
+
+        meta = find_record
+
+        expect(meta).to have_attributes(
+          valid?: true,
+          canonical_slug: wiki_page.slug,
+          title: wiki_page.title,
+          project: wiki_page.wiki.project
+        )
+        expect(meta.slugs.where(slug: last_known_slug)).to exist
+        expect(meta.slugs.canonical.where(slug: wiki_page.slug)).to exist
+      end
+
+      it 'makes a reasonable number of DB queries' do
+        expect(project).to eq(wiki_page.wiki.project)
+
+        expect { find_record }.not_to exceed_query_limit(query_limit)
+      end
+    end
+
+    context 'the slug is too long' do
+      let(:last_known_slug) { FFaker::Lorem.characters(2050) }
+
+      it 'raises an error' do
+        expect { find_record }.to raise_error ActiveRecord::ValueTooLong
+      end
+    end
+
+    context 'a conflicting record exists' do
+      before do
+        create(:wiki_page_meta, project: project, canonical_slug: last_known_slug)
+        create(:wiki_page_meta, project: project, canonical_slug: current_slug)
+      end
+
+      it 'raises an error' do
+        expect { find_record }.to raise_error(ActiveRecord::RecordInvalid)
+      end
+    end
+
+    context 'no existing record exists' do
+      include_examples 'metadata examples' do
+        # The base case is 5 queries:
+        #  - 2 for the outer transaction
+        #  - 1 to find the metadata object if it exists
+        #  - 1 to create it if it does not
+        #  - 1 to insert last_known_slug and current_slug
+        #
+        # (Log has been edited for clarity)
+        # SAVEPOINT active_record_2
+        #
+        # SELECT * FROM wiki_page_meta
+        #   INNER JOIN wiki_page_slugs
+        #     ON wiki_page_slugs.wiki_page_meta_id = wiki_page_meta.id
+        #   WHERE wiki_page_meta.project_id = ?
+        #     AND wiki_page_slugs.canonical = TRUE
+        #     AND wiki_page_slugs.slug IN (?,?)
+        #   LIMIT 2
+        #
+        # INSERT INTO wiki_page_meta (project_id, title) VALUES (?, ?) RETURNING id
+        #
+        # INSERT INTO wiki_page_slugs (wiki_page_meta_id,slug,canonical)
+        #   VALUES (?, ?, ?) (?, ?, ?)
+        #   ON CONFLICT  DO NOTHING RETURNING id
+        #
+        # RELEASE SAVEPOINT active_record_2
+        let(:query_limit) { 5 }
+      end
+    end
+
+    context 'the last_known_slug is the same as the current slug, as on creation' do
+      let(:last_known_slug) { current_slug }
+
+      include_examples 'metadata examples' do
+        # Identical to the base case.
+        let(:query_limit) { 5 }
+      end
+    end
+
+    context 'a record exists in the DB in the correct state' do
+      let(:last_known_slug) { current_slug }
+      let(:old_title) { title }
+
+      before do
+        create_previous_version
+      end
+
+      include_examples 'metadata examples' do
+        # We just need to do the initial query, and the outer transaction
+        # SAVEPOINT active_record_2
+        #
+        # SELECT * FROM wiki_page_meta
+        #   INNER JOIN wiki_page_slugs
+        #     ON wiki_page_slugs.wiki_page_meta_id = wiki_page_meta.id
+        #   WHERE wiki_page_meta.project_id = ?
+        #     AND wiki_page_slugs.canonical = TRUE
+        #     AND wiki_page_slugs.slug = ?
+        #   LIMIT 2
+        #
+        # RELEASE SAVEPOINT active_record_2
+        let(:query_limit) { 3 }
+      end
+    end
+
+    context 'we need to update the slug, but not the title' do
+      let(:old_title) { title }
+
+      before do
+        create_previous_version
+      end
+
+      include_examples 'metadata examples' do
+        # Here we need:
+        #  - 2 for the outer transaction
+        #  - 1 to find the record
+        #  - 1 to insert the new slug
+        #  - 3 to set canonical state correctly
+        #
+        # SAVEPOINT active_record_2
+        #
+        # SELECT * FROM wiki_page_meta
+        #   INNER JOIN wiki_page_slugs
+        #     ON wiki_page_slugs.wiki_page_meta_id = wiki_page_meta.id
+        #   WHERE wiki_page_meta.project_id = ?
+        #     AND wiki_page_slugs.canonical = TRUE
+        #     AND wiki_page_slugs.slug = ?
+        #   LIMIT 1
+        #
+        # INSERT INTO wiki_page_slugs (wiki_page_meta_id,slug,canonical)
+        #   VALUES (?, ?, ?) ON CONFLICT  DO NOTHING RETURNING id
+        #
+        # SELECT * FROM wiki_page_slugs
+        #   WHERE wiki_page_slugs.wiki_page_meta_id = ?
+        #     AND wiki_page_slugs.slug = ?
+        #     LIMIT 1
+        # UPDATE wiki_page_slugs SET canonical = FALSE WHERE wiki_page_meta_id = ?
+        # UPDATE wiki_page_slugs SET canonical = TRUE WHERE id = ?
+        #
+        # RELEASE SAVEPOINT active_record_2
+        let(:query_limit) { 7 }
+      end
+    end
+
+    context 'we need to update the title, but not the slug' do
+      let(:last_known_slug) { wiki_page.slug }
+
+      before do
+        create_previous_version
+      end
+
+      include_examples 'metadata examples' do
+        # Same as minimal case, plus one query to update the title.
+        #
+        # SAVEPOINT active_record_2
+        #
+        # SELECT * FROM wiki_page_meta
+        #   INNER JOIN wiki_page_slugs
+        #     ON wiki_page_slugs.wiki_page_meta_id = wiki_page_meta.id
+        #   WHERE wiki_page_meta.project_id = ?
+        #     AND wiki_page_slugs.canonical = TRUE
+        #     AND wiki_page_slugs.slug = ?
+        #   LIMIT 1
+        #
+        # UPDATE wiki_page_meta SET title = ? WHERE id = ?
+        #
+        # RELEASE SAVEPOINT active_record_2
+        let(:query_limit) { 4 }
+      end
+    end
+
+    context 'we want to change the slug back to a previous version' do
+      let(:slug_1) { 'foo' }
+      let(:slug_2) { 'bar' }
+
+      let(:wiki_page) { create(:wiki_page, title: slug_1, project: project) }
+      let(:last_known_slug) { slug_2 }
+
+      before do
+        meta = create_previous_version(title, slug_1)
+        meta.canonical_slug = slug_2
+      end
+
+      include_examples 'metadata examples' do
+        let(:query_limit) { 7 }
+      end
+    end
+
+    context 'we want to change the slug a bunch of times' do
+      let(:slugs) { generate_list(:sluggified_title, 3) }
+
+      before do
+        meta = create_previous_version
+        slugs.each { |slug| meta.canonical_slug = slug }
+      end
+
+      include_examples 'metadata examples' do
+        let(:query_limit) { 7 }
+      end
+    end
+
+    context 'we need to update the title and the slug' do
+      before do
+        create_previous_version
+      end
+
+      include_examples 'metadata examples' do
+        # -- outer transaction
+        # SAVEPOINT active_record_2
+        #
+        # -- to find the record
+        # SELECT * FROM wiki_page_meta
+        #   INNER JOIN wiki_page_slugs
+        #     ON wiki_page_slugs.wiki_page_meta_id = wiki_page_meta.id
+        #   WHERE wiki_page_meta.project_id = ?
+        #     AND wiki_page_slugs.canonical = TRUE
+        #     AND wiki_page_slugs.slug IN (?,?)
+        #   LIMIT 2
+        #
+        # -- to update the title
+        # UPDATE wiki_page_meta SET title = ? WHERE id = ?
+        #
+        # -- to update slug
+        # INSERT INTO wiki_page_slugs (wiki_page_meta_id,slug,canonical)
+        #   VALUES (?, ?, ?) ON CONFLICT  DO NOTHING RETURNING id
+        #
+        # UPDATE wiki_page_slugs SET canonical = FALSE WHERE wiki_page_meta_id = ?
+        #
+        # SELECT * FROM wiki_page_slugs
+        #   WHERE wiki_page_slugs.wiki_page_meta_id = ?
+        #     AND wiki_page_slugs.slug = ?
+        #     LIMIT 1
+        #
+        # UPDATE wiki_page_slugs SET canonical = TRUE WHERE id = ?
+        #
+        # RELEASE SAVEPOINT active_record_2
+        let(:query_limit) { 8 }
+      end
+    end
+  end
+end

spec/models/wiki_page/slug_spec.rb

+# frozen_string_literal: true
+
+require 'spec_helper'
+
+describe WikiPage::Slug do
+  let_it_be(:meta) { create(:wiki_page_meta) }
+
+  describe 'Associations' do
+    it { is_expected.to belong_to(:wiki_page_meta) }
+
+    it 'refers correctly to the wiki_page_meta' do
+      created = create(:wiki_page_slug, wiki_page_meta: meta)
+
+      expect(created.reload.wiki_page_meta).to eq(meta)
+    end
+  end
+
+  describe 'scopes' do
+    describe 'canonical' do
+      subject { described_class.canonical }
+
+      context 'there are no slugs' do
+        it { is_expected.to be_empty }
+      end
+
+      context 'there are some non-canonical slugs' do
+        before do
+          create(:wiki_page_slug)
+        end
+
+        it { is_expected.to be_empty }
+      end
+
+      context 'there is at least one canonical slugs' do
+        before do
+          create(:wiki_page_slug, :canonical)
+        end
+
+        it { is_expected.not_to be_empty }
+      end
+    end
+  end
+
+  describe 'Validations' do
+    let(:canonical) { false }
+
+    subject do
+      build(:wiki_page_slug, canonical: canonical, wiki_page_meta: meta)
+    end
+
+    it { is_expected.to validate_presence_of(:slug) }
+    it { is_expected.to validate_uniqueness_of(:slug).scoped_to(:wiki_page_meta_id) }
+
+    describe 'only_one_slug_can_be_canonical_per_meta_record' do
+      context 'there are no other slugs' do
+        it { is_expected.to be_valid }
+
+        context 'the current slug is canonical' do
+          let(:canonical) { true }
+
+          it { is_expected.to be_valid }
+        end
+      end
+
+      context 'there are other slugs, but they are not canonical' do
+        before do
+          create(:wiki_page_slug, wiki_page_meta: meta)
+        end
+
+        it { is_expected.to be_valid }
+
+        context 'the current slug is canonical' do
+          let(:canonical) { true }
+
+          it { is_expected.to be_valid }
+        end
+      end
+
+      context 'there is already a canonical slug' do
+        before do
+          create(:wiki_page_slug, canonical: true, wiki_page_meta: meta)
+        end
+
+        it { is_expected.to be_valid }
+
+        context 'the current slug is canonical' do
+          let(:canonical) { true }
+
+          it { is_expected.not_to be_valid }
+        end
+      end
+    end
+  end
+end

spec/models/wiki_page_spec.rb

@@ -606,12 +606,36 @@ describe WikiPage do
       expect(subject).to eq(subject)
     end
 
-    it 'returns false for updated wiki page' do
+    it 'returns true for updated wiki page' do
       subject.update(content: "Updated content")
-      updated_page = wiki.find_page('test page')
+      updated_page = wiki.find_page(existing_page.slug)
 
       expect(updated_page).not_to be_nil
-      expect(updated_page).not_to eq(subject)
+      expect(updated_page).to eq(subject)
+    end
+
+    it 'returns false for a completely different wiki page' do
+      other_page = create(:wiki_page)
+
+      expect(subject.slug).not_to eq(other_page.slug)
+      expect(subject.project).not_to eq(other_page.project)
+      expect(subject).not_to eq(other_page)
+    end
+
+    it 'returns false for page with different slug on same project' do
+      other_page = create(:wiki_page, project: subject.project)
+
+      expect(subject.slug).not_to eq(other_page.slug)
+      expect(subject.project).to eq(other_page.project)
+      expect(subject).not_to eq(other_page)
+    end
+
+    it 'returns false for page with the same slug on a different project' do
+      other_page = create(:wiki_page, title: existing_page.slug)
+
+      expect(subject.slug).to eq(other_page.slug)
+      expect(subject.project).not_to eq(other_page.project)
+      expect(subject).not_to eq(other_page)
     end
   end