`initialize': the scheme postgres does not accept registry part: postgres:@ (or bad hostname?) (URI::InvalidURIError) with Docker

Question

I\'m using Rails with Postgres DB Docker container attached. It looks like I\'m getting below error when I run rails c:

/usr/local/rvm/rubies/ruby-2         


        

Answer 1

The accepted answer is wrong. There's nothing wrong with using DATABASE_URL in your database.yml, although doing so explicitly is probably redundant. The problem is with the value of the URL.

ActiveRecord uses URI::RFC2396_Parser to parse database URLs. The error message above indicates that it's not able to parse the URL, probably because the hostname is missing, cf.

URI::RFC2396_Parser.new.parse('postgres://postgres:@/mydb')
# Traceback (most recent call last):
#       1: from (irb):30
# URI::InvalidURIError (the scheme postgres does not accept registry part: postgres:@ (or bad hostname?))

Other invalid hostnames, such as hostnames with underscores (common in docker-compose setups) will cause similar errors:

URI::RFC2396_Parser.new.parse('postgres://postgres:postgres@my_postgres/mydb')
# Traceback (most recent call last):
#        1: from (irb):34
# URI::InvalidURIError (the scheme postgres does not accept registry part: postgres:postgres@my_postgres (or bad hostname?))

What can be especially confusing is that URI.parse() uses URI::RFC3986_Parser, which is much more forgiving, and will accept either of these "bad" URLs.