Skip to main content
Version: 1.1

Config Groups

 Example

Structured Configs can be used to implement config groups. Special care needs to be taken when specifying a default value for fields populated by a config group. We will look at why below.

Defining a config group for database
@dataclass
class MySQLConfig:
driver: str = "mysql"
host: str = "localhost"
port: int = 3306
@dataclass
class PostGreSQLConfig:
driver: str = "postgresql"
host: str = "localhost"
port: int = 5432
timeout: int = 10
@dataclass
class Config:
# We will populate db using composition.
db: Any
# Create config group `db` with options 'mysql' and 'postgreqsl'
cs = ConfigStore.instance()
cs.store(name="config", node=Config)
cs.store(group="db", name="mysql", node=MySQLConfig)
cs.store(group="db", name="postgresql", node=PostGreSQLConfig)
@hydra.main(config_path=None, config_name="config")
def my_app(cfg: Config) -> None:
print(OmegaConf.to_yaml(cfg))
caution

The Config class is NOT the Defaults list. We will see the Defaults list in the next page.

You can select the database from the command line:

$ python my_app.py +db=postgresql
db:
driver: postgresql
host: localhost
password: drowssap
port: 5432
timeout: 10
user: postgres_user

The + above is required because there is no default choice for the config group db. The next page will reintroduce the Defaults List, eliminating the need for the +.

Config inheritance#

 Example

Standard Python inheritance can be used to get improved type safety, and to move common fields to the parent class.

Defining a config group for database using inheritance
from omegaconf import MISSING
@dataclass
class DBConfig:
host: str = "localhost"
port: int = MISSING
driver: str = MISSING
@dataclass
class MySQLConfig(DBConfig):
driver: str = "mysql"
port: int = 3306
@dataclass
class PostGreSQLConfig(DBConfig):
driver: str = "postgresql"
port: int = 5432
timeout: int = 10
@dataclass
class Config:
# We can now annotate db as DBConfig which
# improves both static and dynamic type safety.
db: DBConfig

Missing fields#

Assign MISSING to a field to indicates that it does not have a default value. This is equivalent to the ??? literal we have seen in OmegaConf configs before.

Omitting a default value is equivalent to assigning MISSING to it, although it is sometimes convenient to be able to assign MISSING it to a field.

caution

Do not confuse omegaconf.MISSING with dataclass.MISSING.

Last updated on by Jasha10