Selecting defaults for config groups

 

After office politics, you decide that you want to use MySQL by default. You no longer want to type +db=mysql every time you run your application.

You can add a defaults list into your config file.

Config group defaults

config.yaml

defaults:
  - db: mysql

Remember to specify the config_name:

@hydra.main(config_path="conf", config_name="config")
def my_app(cfg: DictConfig) -> None:
    print(OmegaConf.to_yaml(cfg))

When you run the updated application, MySQL is loaded by default.

$ python my_app.py
db:
  driver: mysql
  pass: secret
  user: omry

You can have multiple items in the defaults list, e.g

defaults:
 - db: mysql
 - db/mysql/storage_engine: innodb

The defaults are ordered:

• If multiple configs define the same value, the last one wins.
• If multiple configs contribute to the same dictionary, the result is the combined dictionary.

Overriding a config group default

You can still load PostgreSQL, and override individual values.

$ python my_app.py db=postgresql db.timeout=20
db:
  driver: postgresql
  pass: drowssap
  timeout: 20
  user: postgres_user

You can remove a default entry from the defaults list by prefixing it with ~:

$ python my_app.py ~db
{}

Non-config group defaults

Sometimes a config file does not belong in any config group. You can still load it by default. Here is an example for some_file.yaml.

defaults:
  - some_file

Config files that are not part of a config group will always be loaded. They cannot be overridden.
Prefer using a config group.