Create DB tables for storing mentioned users

* Created DB tables for storing mentioned users, groups,
projects referenced in a note on issue, merge request, commit, epic
snippet or on issuable description. Mentioned users, groups, projects
will be stored as an array field in a corresponding table for: issues,
merge requests, commits, epics and snippets.

changelogs/unreleased/21800-mentioned-users-table-migrations.yml

+---
+title: Creates DB tables for storing mentioned users, groups, projects referenced
+  in a note or issuable description
+merge_request: 18316
+author:
+type: added

db/migrate/20191003130045_create_issue_user_mentions.rb

+# frozen_string_literal: true
+
+class CreateIssueUserMentions < ActiveRecord::Migration[5.2]
+  DOWNTIME = false
+
+  def change
+    create_table :issue_user_mentions do |t|
+      t.references :issue, type: :integer, index: false, null: false, foreign_key: { on_delete: :cascade }
+      t.references :note, type: :integer,
+                   index: { where: 'note_id IS NOT NULL', unique: true }, null: true, foreign_key: { on_delete: :cascade }
+      t.integer    :mentioned_users_ids, array: true
+      t.integer    :mentioned_projects_ids, array: true
+      t.integer    :mentioned_groups_ids, array: true
+    end
+
+    add_index :issue_user_mentions, [:issue_id], where: 'note_id is null', unique: true, name: 'issue_user_mentions_on_issue_id_index'
+    add_index :issue_user_mentions, [:issue_id, :note_id], unique: true, name: 'issue_user_mentions_on_issue_id_and_note_id_index'
+  end
+end

db/migrate/20191003150045_create_merge_request_user_mentions.rb

+# frozen_string_literal: true
+
+class CreateMergeRequestUserMentions < ActiveRecord::Migration[5.2]
+  DOWNTIME = false
+
+  def change
+    create_table :merge_request_user_mentions do |t|
+      t.references :merge_request, type: :integer, index: false, null: false, foreign_key: { on_delete: :cascade }
+      t.references :note, type: :integer,
+                   index: { where: 'note_id IS NOT NULL', unique: true }, null: true, foreign_key: { on_delete: :cascade }
+      t.integer    :mentioned_users_ids, array: true
+      t.integer    :mentioned_projects_ids, array: true
+      t.integer    :mentioned_groups_ids, array: true
+    end
+
+    add_index :merge_request_user_mentions, [:merge_request_id], where: 'note_id is null', unique: true, name: 'merge_request_user_mentions_on_mr_id_index'
+    add_index :merge_request_user_mentions, [:merge_request_id, :note_id], unique: true, name: 'merge_request_user_mentions_on_mr_id_and_note_id_index'
+  end
+end

db/migrate/20191003200045_create_epic_user_mentions.rb

+# frozen_string_literal: true
+
+class CreateEpicUserMentions < ActiveRecord::Migration[5.2]
+  DOWNTIME = false
+
+  def change
+    create_table :epic_user_mentions do |t|
+      t.references :epic, type: :integer, index: false, null: false, foreign_key: { on_delete: :cascade }
+      t.references :note, type: :integer,
+                   index: { where: 'note_id IS NOT NULL', unique: true }, null: true, foreign_key: { on_delete: :cascade }
+      t.integer    :mentioned_users_ids, array: true
+      t.integer    :mentioned_projects_ids, array: true
+      t.integer    :mentioned_groups_ids, array: true
+    end
+
+    add_index :epic_user_mentions, [:epic_id], where: 'note_id is null', unique: true, name: 'epic_user_mentions_on_epic_id_index'
+    add_index :epic_user_mentions, [:epic_id, :note_id], unique: true, name: 'epic_user_mentions_on_epic_id_and_note_id_index'
+  end
+end

db/migrate/20191003250045_create_commit_user_mentions.rb

+# frozen_string_literal: true
+
+class CreateCommitUserMentions < ActiveRecord::Migration[5.2]
+  DOWNTIME = false
+
+  def change
+    create_table :commit_user_mentions do |t|
+      t.references :note, type: :integer,
+                   index: { unique: true }, null: false, foreign_key: { on_delete: :cascade }
+      t.binary     :commit_id, null: false
+      t.integer    :mentioned_users_ids, array: true
+      t.integer    :mentioned_projects_ids, array: true
+      t.integer    :mentioned_groups_ids, array: true
+    end
+
+    add_index :commit_user_mentions, [:commit_id, :note_id], name: 'commit_user_mentions_on_commit_id_and_note_id_index'
+  end
+end

db/migrate/20191003300045_create_snippet_user_mentions.rb

+# frozen_string_literal: true
+
+class CreateSnippetUserMentions < ActiveRecord::Migration[5.2]
+  DOWNTIME = false
+
+  def change
+    create_table :snippet_user_mentions do |t|
+      t.references :snippet, type: :integer, index: false, null: false, foreign_key: { on_delete: :cascade }
+      t.references :note, type: :integer,
+                   index: { where: 'note_id IS NOT NULL', unique: true }, null: true, foreign_key: { on_delete: :cascade }
+      t.integer    :mentioned_users_ids, array: true
+      t.integer    :mentioned_projects_ids, array: true
+      t.integer    :mentioned_groups_ids, array: true
+    end
+
+    add_index :snippet_user_mentions, [:snippet_id], where: 'note_id is null', unique: true, name: 'snippet_user_mentions_on_snippet_id_index'
+    add_index :snippet_user_mentions, [:snippet_id, :note_id], unique: true, name: 'snippet_user_mentions_on_snippet_id_and_note_id_index'
+  end
+end

db/migrate/20191003350045_create_design_user_mentions.rb

+# frozen_string_literal: true
+
+class CreateDesignUserMentions < ActiveRecord::Migration[5.2]
+  DOWNTIME = false
+
+  def change
+    create_table :design_user_mentions do |t|
+      t.references :design, type: :integer, index: false, null: false,
+                   foreign_key: { to_table: :design_management_designs, column: :design_id, on_delete: :cascade }
+      t.references :note, type: :integer,
+                   index: { unique: true }, null: false, foreign_key: { on_delete: :cascade }
+      t.integer    :mentioned_users_ids, array: true
+      t.integer    :mentioned_projects_ids, array: true
+      t.integer    :mentioned_groups_ids, array: true
+    end
+
+    add_index :design_user_mentions, [:design_id, :note_id], name: 'design_user_mentions_on_design_id_and_note_id_index'
+  end
+end

db/schema.rb

@@ -1198,6 +1198,16 @@ ActiveRecord::Schema.define(version: 2019_11_15_091425) do
     t.index ["project_id"], name: "index_clusters_kubernetes_namespaces_on_project_id"
   end
 
+  create_table "commit_user_mentions", force: :cascade do |t|
+    t.integer "note_id", null: false
+    t.binary "commit_id", null: false
+    t.integer "mentioned_users_ids", array: true
+    t.integer "mentioned_projects_ids", array: true
+    t.integer "mentioned_groups_ids", array: true
+    t.index ["commit_id", "note_id"], name: "commit_user_mentions_on_commit_id_and_note_id_index"
+    t.index ["note_id"], name: "index_commit_user_mentions_on_note_id", unique: true
+  end
+
   create_table "container_repositories", id: :serial, force: :cascade do |t|
     t.integer "project_id", null: false
     t.string "name", null: false
@@ -1361,6 +1371,16 @@ ActiveRecord::Schema.define(version: 2019_11_15_091425) do
     t.index ["sha", "issue_id"], name: "index_design_management_versions_on_sha_and_issue_id", unique: true
   end
 
+  create_table "design_user_mentions", force: :cascade do |t|
+    t.integer "design_id", null: false
+    t.integer "note_id", null: false
+    t.integer "mentioned_users_ids", array: true
+    t.integer "mentioned_projects_ids", array: true
+    t.integer "mentioned_groups_ids", array: true
+    t.index ["design_id", "note_id"], name: "design_user_mentions_on_design_id_and_note_id_index"
+    t.index ["note_id"], name: "index_design_user_mentions_on_note_id", unique: true
+  end
+
   create_table "draft_notes", force: :cascade do |t|
     t.integer "merge_request_id", null: false
     t.integer "author_id", null: false
@@ -1433,6 +1453,17 @@ ActiveRecord::Schema.define(version: 2019_11_15_091425) do
     t.index ["epic_id"], name: "index_epic_metrics"
   end
 
+  create_table "epic_user_mentions", force: :cascade do |t|
+    t.integer "epic_id", null: false
+    t.integer "note_id"
+    t.integer "mentioned_users_ids", array: true
+    t.integer "mentioned_projects_ids", array: true
+    t.integer "mentioned_groups_ids", array: true
+    t.index ["epic_id", "note_id"], name: "epic_user_mentions_on_epic_id_and_note_id_index", unique: true
+    t.index ["epic_id"], name: "epic_user_mentions_on_epic_id_index", unique: true, where: "(note_id IS NULL)"
+    t.index ["note_id"], name: "index_epic_user_mentions_on_note_id", unique: true, where: "(note_id IS NOT NULL)"
+  end
+
   create_table "epics", id: :serial, force: :cascade do |t|
     t.integer "milestone_id"
     t.integer "group_id", null: false
@@ -1978,6 +2009,17 @@ ActiveRecord::Schema.define(version: 2019_11_15_091425) do
     t.index ["service_id"], name: "index_issue_tracker_data_on_service_id"
   end
 
+  create_table "issue_user_mentions", force: :cascade do |t|
+    t.integer "issue_id", null: false
+    t.integer "note_id"
+    t.integer "mentioned_users_ids", array: true
+    t.integer "mentioned_projects_ids", array: true
+    t.integer "mentioned_groups_ids", array: true
+    t.index ["issue_id", "note_id"], name: "issue_user_mentions_on_issue_id_and_note_id_index", unique: true
+    t.index ["issue_id"], name: "issue_user_mentions_on_issue_id_index", unique: true, where: "(note_id IS NULL)"
+    t.index ["note_id"], name: "index_issue_user_mentions_on_note_id", unique: true, where: "(note_id IS NOT NULL)"
+  end
+
   create_table "issues", id: :serial, force: :cascade do |t|
     t.string "title"
     t.integer "author_id"
@@ -2333,6 +2375,17 @@ ActiveRecord::Schema.define(version: 2019_11_15_091425) do
     t.index ["pipeline_id"], name: "index_merge_request_metrics_on_pipeline_id"
   end
 
+  create_table "merge_request_user_mentions", force: :cascade do |t|
+    t.integer "merge_request_id", null: false
+    t.integer "note_id"
+    t.integer "mentioned_users_ids", array: true
+    t.integer "mentioned_projects_ids", array: true
+    t.integer "mentioned_groups_ids", array: true
+    t.index ["merge_request_id", "note_id"], name: "merge_request_user_mentions_on_mr_id_and_note_id_index", unique: true
+    t.index ["merge_request_id"], name: "merge_request_user_mentions_on_mr_id_index", unique: true, where: "(note_id IS NULL)"
+    t.index ["note_id"], name: "index_merge_request_user_mentions_on_note_id", unique: true, where: "(note_id IS NOT NULL)"
+  end
+
   create_table "merge_requests", id: :serial, force: :cascade do |t|
     t.string "target_branch", null: false
     t.string "source_branch", null: false
@@ -3540,6 +3593,17 @@ ActiveRecord::Schema.define(version: 2019_11_15_091425) do
     t.index ["user_id"], name: "index_smartcard_identities_on_user_id"
   end
 
+  create_table "snippet_user_mentions", force: :cascade do |t|
+    t.integer "snippet_id", null: false
+    t.integer "note_id"
+    t.integer "mentioned_users_ids", array: true
+    t.integer "mentioned_projects_ids", array: true
+    t.integer "mentioned_groups_ids", array: true
+    t.index ["note_id"], name: "index_snippet_user_mentions_on_note_id", unique: true, where: "(note_id IS NOT NULL)"
+    t.index ["snippet_id", "note_id"], name: "snippet_user_mentions_on_snippet_id_and_note_id_index", unique: true
+    t.index ["snippet_id"], name: "snippet_user_mentions_on_snippet_id_index", unique: true, where: "(note_id IS NULL)"
+  end
+
   create_table "snippets", id: :serial, force: :cascade do |t|
     t.string "title"
     t.text "content"
@@ -4258,6 +4322,7 @@ ActiveRecord::Schema.define(version: 2019_11_15_091425) do
   add_foreign_key "clusters_kubernetes_namespaces", "clusters", on_delete: :cascade
   add_foreign_key "clusters_kubernetes_namespaces", "environments", on_delete: :nullify
   add_foreign_key "clusters_kubernetes_namespaces", "projects", on_delete: :nullify
+  add_foreign_key "commit_user_mentions", "notes", on_delete: :cascade
   add_foreign_key "container_repositories", "projects"
   add_foreign_key "dependency_proxy_blobs", "namespaces", column: "group_id", on_delete: :cascade
   add_foreign_key "dependency_proxy_group_settings", "namespaces", column: "group_id", on_delete: :cascade
@@ -4275,6 +4340,8 @@ ActiveRecord::Schema.define(version: 2019_11_15_091425) do
   add_foreign_key "design_management_designs_versions", "design_management_versions", column: "version_id", name: "fk_f4d25ba00c", on_delete: :cascade
   add_foreign_key "design_management_versions", "issues", on_delete: :cascade
   add_foreign_key "design_management_versions", "users", column: "author_id", name: "fk_c1440b4896", on_delete: :nullify
+  add_foreign_key "design_user_mentions", "design_management_designs", column: "design_id", on_delete: :cascade
+  add_foreign_key "design_user_mentions", "notes", on_delete: :cascade
   add_foreign_key "draft_notes", "merge_requests", on_delete: :cascade
   add_foreign_key "draft_notes", "users", column: "author_id", on_delete: :cascade
   add_foreign_key "elasticsearch_indexed_namespaces", "namespaces", on_delete: :cascade
@@ -4283,6 +4350,8 @@ ActiveRecord::Schema.define(version: 2019_11_15_091425) do
   add_foreign_key "epic_issues", "epics", on_delete: :cascade
   add_foreign_key "epic_issues", "issues", on_delete: :cascade
   add_foreign_key "epic_metrics", "epics", on_delete: :cascade
+  add_foreign_key "epic_user_mentions", "epics", on_delete: :cascade
+  add_foreign_key "epic_user_mentions", "notes", on_delete: :cascade
   add_foreign_key "epics", "epics", column: "due_date_sourcing_epic_id", name: "fk_013c9f36ca", on_delete: :nullify
   add_foreign_key "epics", "epics", column: "parent_id", name: "fk_25b99c1be3", on_delete: :cascade
   add_foreign_key "epics", "epics", column: "start_date_sourcing_epic_id", name: "fk_9d480c64b2", on_delete: :nullify
@@ -4350,6 +4419,8 @@ ActiveRecord::Schema.define(version: 2019_11_15_091425) do
   add_foreign_key "issue_links", "issues", column: "target_id", name: "fk_e71bb44f1f", on_delete: :cascade
   add_foreign_key "issue_metrics", "issues", on_delete: :cascade
   add_foreign_key "issue_tracker_data", "services", on_delete: :cascade
+  add_foreign_key "issue_user_mentions", "issues", on_delete: :cascade
+  add_foreign_key "issue_user_mentions", "notes", on_delete: :cascade
   add_foreign_key "issues", "issues", column: "duplicated_to_id", name: "fk_9c4516d665", on_delete: :nullify
   add_foreign_key "issues", "issues", column: "moved_to_id", name: "fk_a194299be1", on_delete: :nullify
   add_foreign_key "issues", "milestones", name: "fk_96b1dd429c", on_delete: :nullify
@@ -4389,6 +4460,8 @@ ActiveRecord::Schema.define(version: 2019_11_15_091425) do
   add_foreign_key "merge_request_metrics", "merge_requests", on_delete: :cascade
   add_foreign_key "merge_request_metrics", "users", column: "latest_closed_by_id", name: "fk_ae440388cc", on_delete: :nullify
   add_foreign_key "merge_request_metrics", "users", column: "merged_by_id", name: "fk_7f28d925f3", on_delete: :nullify
+  add_foreign_key "merge_request_user_mentions", "merge_requests", on_delete: :cascade
+  add_foreign_key "merge_request_user_mentions", "notes", on_delete: :cascade
   add_foreign_key "merge_requests", "ci_pipelines", column: "head_pipeline_id", name: "fk_fd82eae0b9", on_delete: :nullify
   add_foreign_key "merge_requests", "merge_request_diffs", column: "latest_merge_request_diff_id", name: "fk_06067f5644", on_delete: :nullify
   add_foreign_key "merge_requests", "milestones", name: "fk_6a5165a692", on_delete: :nullify
@@ -4509,6 +4582,8 @@ ActiveRecord::Schema.define(version: 2019_11_15_091425) do
   add_foreign_key "services", "projects", name: "fk_71cce407f9", on_delete: :cascade
   add_foreign_key "slack_integrations", "services", on_delete: :cascade
   add_foreign_key "smartcard_identities", "users", on_delete: :cascade
+  add_foreign_key "snippet_user_mentions", "notes", on_delete: :cascade
+  add_foreign_key "snippet_user_mentions", "snippets", on_delete: :cascade
   add_foreign_key "snippets", "projects", name: "fk_be41fd4bb7", on_delete: :cascade
   add_foreign_key "software_license_policies", "projects", on_delete: :cascade
   add_foreign_key "software_license_policies", "software_licenses", on_delete: :cascade

spec/db/schema_spec.rb

@@ -79,7 +79,8 @@ describe 'Database schema' do
     vulnerability_identifiers: %w[external_id],
     vulnerability_scanners: %w[external_id],
     web_hooks: %w[service_id group_id],
-    suggestions: %w[commit_id]
+    suggestions: %w[commit_id],
+    commit_user_mentions: %w[commit_id]
   }.with_indifferent_access.freeze
 
   context 'for table' do