Selecting multiple configs from a Config Group in Hydra without using an explicit nesting level inside each of the configs

Question

The documentation in https://hydra.cc/docs/patterns/select_multiple_configs_from_config_group/ shows how to pick multiple configs from a Config Group and place them in a dictionary-like structure.

However, as mentioned in the very last paragraph there, "example uses an explicit nesting level inside each of the configs to prevent them stepping over one another" . For my use-case, this would prove extremely cumbersome and I would like to avoid it at all costs if possible.

Is there a way to achieve a similar result without resorting to explicitly adding the level in the individual configs? Thanks in advance:)

Answer 1

You can use a defaults-list @package keyword to achieve a similar result.

Let's assume you have changed the yaml files server/site/fb.yaml and server/site/google.yaml to not contain the "explicit nesting", so eg server/site/fb.yaml contains only the data domain: facebook.com .

You can achieve the same output as from the docs webpage using the following defaults list in server/apache.yaml`:

# Option 1: With a non-overridable defaults list
defaults:
  - site/fb@site.fb
  - site/google@site.google
# Option 2: With an overridable defaults list
defaults:
  - site@site.fb: fb
  - site@site.google: google

Either option 1 or option 2 above produces this output:

$ python my_app.py
server:
  site:
    fb:
      domain: facebook.com
    google:
      domain: google.com
  host: localhost
  port: 443

The @package directive here could be any compound key that you want. For example, using the following defaults list:

# Option 1: With a non-overridable defaults list
defaults:
  - site/fb@foo
  - site/google@bar
# Option 2: With an overridable defaults list
defaults:
  - site@foo: fb
  - site@bar: google

We get this result:

$ python my_app.py
server:
  foo:
    domain: facebook.com
  bar:
    domain: google.com
  host: localhost
  port: 443

Using option 2 (an overridable defaults list) means you can override the given default option using the CLI:

$ python my_app.py server/site@server.foo=amazon
server:
  foo:
    domain: amazon.com
  bar:
    domain: google.com
  host: localhost
  port: 443