How can I remove an enum label from pg_enum table in Google Cloud SQL? - postgresql

Question

I have a Node app (Express) that I built recently, which uses Sequelize to connect to a PostgreSQL instance. I just deployed this to GCP and used Cloud SQL to set up the database. This works quite well and the app properly connects to the DB instance.
However, when running the migrations I have I get this error: permission denied for table pg_enum
This happens on a single migration that I have which tries to remove an enum value from the database:
module.exports = {
up: (queryInterface, Sequelize) =>
queryInterface.sequelize.query(
`DELETE FROM pg_enum WHERE enumlabel = 'to' AND enumtypid = (SELECT oid FROM pg_type WHERE typname = 'enum_Subscriptions_emailType')`
),
down: (queryInterface, Sequelize) =>
queryInterface.sequelize.query(`ALTER TYPE "enum_Subscriptions_emailType" ADD VALUE 'to';`)
}
I've read here that since Cloud SQL is a managed service, it doesn't provide superuser privileges to customers like me. Is there some other way that I can get this migration run?
I've also tried running a Cloud Build process, but that also fails with the following error: ERROR: connect ENOENT /cloudsql/<project-id>:<project-region>:<db-instance>/.s.PGSQL.5432. For reference, my cloudbuild.yaml file looked like this:
steps:
- name: 'gcr.io/cloud-builders/yarn'
args: ['install']
- name: 'gcr.io/cloud-builders/yarn'
args: ['migrate']
- name: 'gcr.io/cloud-builders/gcloud'
args: ['app', 'deploy']
and my package.json scripts were:
"scripts": {
"start": "node index.js",
"migrate": "npx sequelize-cli db:migrate",
"dev": "set DEBUG=app:* && nodemon index.js",
"deploy": "gcloud builds submit --config cloudbuild.yaml ."
}
What else can I do to get around this, so that the migrations I have following this one can run and my app can function?

Answer 1

Removing a value from an enum is not supported by PostgreSQL. You can only add new ones or rename existing ones.
While it might work somewhat reliably by modifying the system catalogue, even this is not officially supported and needs superuser permissions for a reason - so there is no way to do it without.
The supported way to do what you want to do is to recreate the type without the value.
CREATE TYPE new_enum AS ENUM('a','b','c');
ALTER TABLE table_using_old_enum
ALTER COLUMN colum_using_old_enum
SET DATA TYPE new_enum
USING colum_using_old_enum::text::new_enum;
DROP TYPE old_enum;
ALTER TYPE new_enum RENAME TO old_enum;
This obviously only works if no entry in table_using_old_type is still set to the value that you want to remove - you need to ensure this first, otherwise the typecast in the USING clause will fail for those values.
--
Alternatively, you could also just comment out that query - if you already know that a few minutes later with a later migration the type will be removed completely, it shouldn't cause an issue if that value stays in until then.