Add uniq db index on project_id+iid

db/migrate/20140416074002_add_index_on_iid.rb

+class AddIndexOnIid < ActiveRecord::Migration
+  def change
+    add_index :issues, [:project_id, :iid], unique: true
+    add_index :merge_requests, [:target_project_id, :iid], unique: true
+    add_index :milestones, [:project_id, :iid], unique: true
+  end
+end

db/schema.rb

@@ -93,6 +93,7 @@ ActiveRecord::Schema.define(version: 20140416185734) do
   add_index "issues", ["author_id"], name: "index_issues_on_author_id", using: :btree
   add_index "issues", ["created_at"], name: "index_issues_on_created_at", using: :btree
   add_index "issues", ["milestone_id"], name: "index_issues_on_milestone_id", using: :btree
+  add_index "issues", ["project_id", "iid"], name: "index_issues_on_project_id_and_iid", unique: true, using: :btree
   add_index "issues", ["project_id"], name: "index_issues_on_project_id", using: :btree
   add_index "issues", ["title"], name: "index_issues_on_title", using: :btree
 
@@ -143,6 +144,7 @@ ActiveRecord::Schema.define(version: 20140416185734) do
   add_index "merge_requests", ["source_branch"], name: "index_merge_requests_on_source_branch", using: :btree
   add_index "merge_requests", ["source_project_id"], name: "index_merge_requests_on_source_project_id", using: :btree
   add_index "merge_requests", ["target_branch"], name: "index_merge_requests_on_target_branch", using: :btree
+  add_index "merge_requests", ["target_project_id", "iid"], name: "index_merge_requests_on_target_project_id_and_iid", unique: true, using: :btree
   add_index "merge_requests", ["title"], name: "index_merge_requests_on_title", using: :btree
 
   create_table "milestones", force: true do |t|
@@ -157,6 +159,7 @@ ActiveRecord::Schema.define(version: 20140416185734) do
   end
 
   add_index "milestones", ["due_date"], name: "index_milestones_on_due_date", using: :btree
+  add_index "milestones", ["project_id", "iid"], name: "index_milestones_on_project_id_and_iid", unique: true, using: :btree
   add_index "milestones", ["project_id"], name: "index_milestones_on_project_id", using: :btree
 
   create_table "namespaces", force: true do |t|