Alter table modify enum in Knex js for Postgresql gives error

You first need to drop the existing constraint, and create a new one with the new values. The code sample below should help.

exports.up = function(knex, Promise) {
  return knex.schema.raw(`
    ALTER TABLE "car" DROP CONSTRAINT "car_fuel_type_check";
    ALTER TABLE "car" ADD CONSTRAINT "car_fuel_type_check" CHECK (fuel_type IN ('HYBRID'::text, 'ELECTRIC'::text, 'PETROL'::text, 'DIESEL'::text))
  `);
};

// The reverse migration is similar
exports.down = function(knex, Promise) {
  return knex.schema.raw(`
    ALTER TABLE "car" DROP CONSTRAINT "car_fuel_type_check";
    ALTER TABLE "car" ADD CONSTRAINT "car_fuel_type_check" CHECK (fuel_type IN ('PETROL'::text, 'DIESEL'::text, 'CNG'::text));
  `);
};

I'm assuming your constraint name is car_fuel_type_check. If not, you should replace car_fuel_type_check with your constraint name.

Alter column does not work for enum types in knex 0.13.0.

Also enums are implemented as check constraints, so to change it you need to recreate the.

Something like this:

exports.up = function(knex, Promise) {
  return knex.schema.raw(`
    ALTER TABLE "car"
    DROP CONSTRAINT "car_fuel_type_check",
    ADD CONSTRAINT "car_fuel_type_check" 
    CHECK (fuel_type IN ('HYBRID', 'ELECTRIC', 'PETROL', 'DIESEL'))
  `);
};

exports.down = function(knex, Promise) { ... };

You might need to check your constraint name that was originally generated by knex from the DB.

Currently knex.schema.raw is the only way to modify enums.