Specify Postgres version in ActiveRecord config

Question

I have multiple versions of PostgreSQL running on my machine (running Ubuntu Trusty).

$ service postgresql status
9.1/main (port 5433): online
9.5/main (port 5432): online

I am running several Ruby apps with ActiveRecord, that are each using different versions of Postgres, and I want to be able to specify the Postgres version in database.yml, something like this:

default: &default
  adapter: postgresql
  encoding: utf8
  version: 9.1
  # ... or, since this seems to be close to pg_wrapper's syntax:
  cluster: 9.1/main

What I don't want to have to do is specify port: 5433, since that's likely to be different for each version on each machine it's running on. Is there a way to do this?

Why keep database connection details in version control in the first place? IMO . gitignore it and have everyone fill it in with their own details or set DATABASE_URL in the environment. — D-side
– D-side, Commented Jul 21, 2016 at 8:37
Yeah, great, cos they're all sure to get all the details right. — PJSCopeland
– PJSCopeland, Commented Jul 21, 2016 at 8:38
They probably know their machines better, right? This cluster-thingy, as far as I know, is Debian-specific. Are you expecting everyone to be on Debian (or derivatives, like Ubuntu)? Also note that pg_wrapper only affects utilities that Rails doesn't use (probably with the exception of pg_dump for schema in SQL). — D-side
– D-side, Commented Jul 21, 2016 at 8:54

mu is too short · Accepted Answer · 2016-07-21 08:07:20Z

2

You can put environment variables in your database.yml using a bit of ERB:

default: &default
  adapter: postgresql
  encoding: utf8
  port: <%= ENV['POSTGRESQL_91_PORT'] %>

That way your database.yml files are the same on your various machines and you just need to set up some machine-specific environment settings.

answered Jul 21, 2016 at 8:07

mu is too short

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6 Comments

PJSCopeland Over a year ago

Hmmm... But I want to have it set once, in the repository, so I don't have to keep setting it up on every machine.

mu is too short Over a year ago

I don't think you can, Rails isn't going to know how to figure out which versions of PostgreSQL are running and which ports they're using on any random machine; suppose you have an Ubuntu box, a Debian box, a couple macs, how do you expect Rails to know what is running where? Environment variables are the standard way of doing this sort of thing, most apps I build end up with a handful of environment variables to deal with the differences between different developer machines, staging servers, and production servers.

PJSCopeland Over a year ago

Well, like I mentioned, there's pg_wrapper. Any Postgres command line script can take the option --cluster=9.1/main and choose the right service. Why not ActiveRecord's adapter?

mu is too short Over a year ago

You're welcome to submit a patch to Rails if setting environment variables is too difficult to manage.

PJSCopeland Over a year ago

How about: port: <%= `service postgresql status`.match(/9\.1\/main \(port (\d+)\)/)[1] %>? (Then again, that's probably still Ubuntu-specific...)

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