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Discussion on: Development environment for Elixir + Phoenix with Docker and Docker-compose

hlappa profile image
Aleksi Holappa Author

Good question! I'm running my tests inside the local development container with command docker-compose run -e MIX_ENV=test web mix test. That command will replace the MIX_ENV environment variable with value "test", so when the mix test is executed the mix environment is set to test, not dev.

About the database url, the smartest way to use environment defined database URL is to use wildcard character in the database name, for example, postgres://postgres:postgres@db:5432/myapp_?. This way in the config files we can read that URL from container environment, replace the ? with our actual environment respectively (dev, test, even prod). By going this, you will always have separate databases locally for development and testing, and the development data does not affect test cases.

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nycplayer profile image
Matt Van Horn

Is that wildcard substitution something I do manually w/ String.replace or interpolation, or is there something built-in to the config function that I am unaware of?
So far the only thing I got to work was:
# .env
DATABASE_URL=postgres://postgres:postgres@db:5432/my_app_

# dev.exs
database_url = "#{System.get_env("DATABASE_URL")}#{Mix.env()}"

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hlappa profile image
Aleksi Holappa Author

That Mix.env() is one way to achieve that. Personally I would still use String.replace/3, since Elixir 1.9 introduced a new way to configure your application without Mix dependency in your config-files.

I would do it this way:

test.exs

database_url = System.get_env("DATABASE_URL")

config :myapp, Myapp.Repo,
  url: String.replace(database_url, "?", "test"),
  pool: Ecto.Adapters.SQL.Sandbox

.env

DATABASE_URL=postgres://postgres:postgres@db:5432/myapp__?