Revert "Remove issues.assignee_id column"

This reverts commit 8c0ab358.

db/migrate/20170523073948_remove_assignee_id_from_issue.rb

-# See http://doc.gitlab.com/ce/development/migration_style_guide.html
-# for more information on how to write migrations for GitLab.
-
-class RemoveAssigneeIdFromIssue < ActiveRecord::Migration
-  include Gitlab::Database::MigrationHelpers
-
-  # Set this constant to true if this migration requires downtime.
-  DOWNTIME = false
-
-  # When a migration requires downtime you **must** uncomment the following
-  # constant and define a short and easy to understand explanation as to why the
-  # migration requires downtime.
-  # DOWNTIME_REASON = ''
-
-  # When using the methods "add_concurrent_index", "remove_concurrent_index" or
-  # "add_column_with_default" you must disable the use of transactions
-  # as these methods can not run in an existing transaction.
-  # When using "add_concurrent_index" or "remove_concurrent_index" methods make sure
-  # that either of them is the _only_ method called in the migration,
-  # any other changes should go in a separate migration.
-  # This ensures that upon failure _only_ the index creation or removing fails
-  # and can be retried or reverted easily.
-  #
-  # To disable transactions uncomment the following line and remove these
-  # comments:
-  disable_ddl_transaction!
-
-  def up
-    remove_column :issues, :assignee_id
-  end
-
-  def down
-    add_column :issues, :assignee_id, :integer
-    add_concurrent_index :issues, :assignee_id
-  end
-end

db/schema.rb

@@ -11,7 +11,7 @@
 #
 # It's strongly recommended that you check this file into your version control system.
 
-ActiveRecord::Schema.define(version: 20170523073948) do
+ActiveRecord::Schema.define(version: 20170516183131) do
 
   # These are extensions that must be enabled in order to support this database
   enable_extension "plpgsql"
@@ -567,6 +567,7 @@ ActiveRecord::Schema.define(version: 20170523073948) do
 
   create_table "issues", force: :cascade do |t|
     t.string "title"
+    t.integer "assignee_id"
     t.integer "author_id"
     t.integer "project_id"
     t.datetime "created_at"
@@ -595,6 +596,7 @@ ActiveRecord::Schema.define(version: 20170523073948) do
     t.integer "last_edited_by_id"
   end
 
+  add_index "issues", ["assignee_id"], name: "index_issues_on_assignee_id", using: :btree
   add_index "issues", ["author_id"], name: "index_issues_on_author_id", using: :btree
   add_index "issues", ["confidential"], name: "index_issues_on_confidential", using: :btree
   add_index "issues", ["created_at"], name: "index_issues_on_created_at", using: :btree