I wanted to use an external Database with my heroku application. But I'm unable to edit the configuration cariables. I tried using GUI, Which says, Cannot overwrite attachment values DATABASE_URL. While I tried using CLI as well. I used the command: heroku config:addDATABASE_URL="postgresql://username:password@IP:PORT". However, this throws an error ... is not a heroku command.
After trying out most these answers, I came across an update in 2016, here: the database needs to be detached first, then update the variable of the DATABASE_URL.
heroku addons:attach heroku-postgresql -a <app_name> --as HEROKU_DATABASE
heroku addons:detach DATABASE -a <app_name>
heroku config:add DATABASE_URL=
An alternative method which does not require detaching (which may not be a desired outcome of the switch) is to simply attach the new database and then promote it, which the Heroku Documents explicitly states as a way to set the DATABASE_URL.
heroku addons:attach heroku-postgresql -a <app_name>
heroku pg:promote heroku-postgresql -a <app_name>
As explained in this article, the correct syntax to set/add a configuration variable is
$ heroku config:set DATABASE_URL="postgresql://username:password@IP:PORT"
However, it looks like (see the comments) the DATABASE_URL has been deprecated and trying to update it will trigger an error.
I got the very same situation today when I need to change postgres to postgis. Detach doesn't work for me so I done this to database.yml:
production:
url: <%= ENV['DATABASE_URL'].sub(/^postgres/, "postgis") %>
https://github.com/rgeo/activerecord-postgis-adapter/issues/214.
Solved it. Just for the reference of the users who have the same issue or want to have a similar implementation. Here's the workaround which worked for me.
Heroku no more overwrites databse.yml, so I just modified the DATBASE_URL in the database.yml and pushed it :)
It worked too!
Source : https://discussion.heroku.com/t/rails-4-1-database-yml-no-longer-overwritten-on-heroku/550
Based on the Heroku docs this is how you would share a database with multiple apps.
heroku addons:attach my-originating-app::DATABASE --app sushi
来源：https://stackoverflow.com/questions/35061914/how-to-change-database-url-for-a-heroku-application