Allow SlackService while migratingallow-slack-service

1. Make the existing migration converting SlackService ->
   SlackNotificationService a no-op.
2. Allow SlackService as an alternative class name for
   SlackNotificationService. This also means that `#to_param` returns
   the same thing for both classes, so the UI will work in either case.
3. Create a post-deployment migration to update the existing service
   names in batches.

In a future release, we can remove the dummy SlackService class.

4 files changed, 26 insertions, 9 deletions

diff --git a/app/models/project_services/slack_service.rb b/app/models/project_services/slack_service.rb
new file mode 100644
index 00000000000..7324bb8c7e0
--- /dev/null
+++ b/app/models/project_services/slack_service.rb
@@ -0,0 +1,4 @@
+# Remove this in 9.0, this is just to allow a post-deployment migration to
+# rename the service. See https://gitlab.com/gitlab-org/gitlab-ce/issues/25855
+class SlackService < SlackNotificationService
+end
diff --git a/db/migrate/20161213172958_change_slack_service_to_slack_notification_service.rb b/db/migrate/20161213172958_change_slack_service_to_slack_notification_service.rb
index a7278d7b5a6..db839bb3000 100644
--- a/db/migrate/20161213172958_change_slack_service_to_slack_notification_service.rb
+++ b/db/migrate/20161213172958_change_slack_service_to_slack_notification_service.rb
@@ -1,14 +1,10 @@
 class ChangeSlackServiceToSlackNotificationService < ActiveRecord::Migration
   include Gitlab::Database::MigrationHelpers
 
-  DOWNTIME = true
-  DOWNTIME_REASON = 'Rename SlackService to SlackNotificationService'
+  DOWNTIME = false
 
-  def up
-    execute("UPDATE services SET type = 'SlackNotificationService' WHERE type = 'SlackService'")
-  end
-
-  def down
-    execute("UPDATE services SET type = 'SlackService' WHERE type = 'SlackNotificationService'")
+  # This migration is a no-op, as it existed in an RC but was then moved:
+  #   db/post_migrate/20161220101029_change_slack_service_to_slack_notification_service_in_batches.rb
+  def change
   end
 end
diff --git a/db/post_migrate/20161220101029_change_slack_service_to_slack_notification_service_in_batches.rb b/db/post_migrate/20161220101029_change_slack_service_to_slack_notification_service_in_batches.rb
new file mode 100644
index 00000000000..fd1405298a2
--- /dev/null
+++ b/db/post_migrate/20161220101029_change_slack_service_to_slack_notification_service_in_batches.rb
@@ -0,0 +1,17 @@
+class ChangeSlackServiceToSlackNotificationServiceInBatches < ActiveRecord::Migration
+  include Gitlab::Database::MigrationHelpers
+
+  DOWNTIME = false
+
+  def up
+    update_column_in_batches(:services, :type, 'SlackNotificationService') do |table, query|
+      query.where(table[:type].eq('SlackService'))
+    end
+  end
+
+  def down
+    update_column_in_batches(:services, :type, 'SlackService') do |table, query|
+      query.where(table[:type].eq('SlackNotificationService'))
+    end
+  end
+end
diff --git a/db/schema.rb b/db/schema.rb
index 14801b581e6..b17ec20e482 100644
--- a/db/schema.rb
+++ b/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: 20161213172958) do
+ActiveRecord::Schema.define(version: 20161220101029) do
 
   # These are extensions that must be enabled in order to support this database
   enable_extension "plpgsql"