Rails + Postgres migration - why am I receiving the error "PG::UndefinedFunction: ERROR: function gen_random_uuid() does not exist"?
The issue was that the uuid-ossp extension was being blown away with the database each time I dropped the db as part of a reset and migration (e.g. rake db:drop db:create db:migrate).
The fix is to create a migration that's run before all other migrations which enables the relevant extension(s). Like so (db/migrate/0_enable_extensions.rb):
class EnableExtensions < ActiveRecord::Migration[5.1] def change enable_extension 'uuid-ossp' enable_extension 'pgcrypto' endend
Edge case answer:
Add the migration enabling the extension as stated above.
If you've previously had bigint id's and you're converting over to UUID, running rake db:reset db:migrate failed for me. Be sure to run rake db:drop db:create db:migrate as stated above!
If you get the error Environment data not found in the schema, run bin/rails db:environment:set RAILS_ENV=development.