Version: 1.0

Structured config schema


We have seen how to use Structured Configs as configuration, but they can also be used as a schema (i.e. validating configuration files).

When Hydra loads a config file, it looks in the ConfigStore for a Structured Config with a matching name and group. If found, it is used as the schema for the newly loaded config.

This page shows how to validate db/mysql.yaml and db/postgresql.yaml files against a pre-defined schema.

Given the config directory structure:

โ”œโ”€โ”€ config.yaml
โ””โ”€โ”€ db
โ”œโ”€โ”€ mysql.yaml
โ””โ”€โ”€ postgresql.yaml

We can add Structured Configs for mysql.yaml and postgresql.yaml, providing a schema for validating them.

The Structured Configs below are stored as db/mysql and db/postgresql. They will be used as schema when we load their corresponding config files.
class DBConfig:
driver: str = MISSING
host: str = "localhost"
port: int = MISSING
class MySQLConfig(DBConfig):
driver: str = "mysql"
port: int = 3306
user: str = MISSING
password: str = MISSING
class PostGreSQLConfig(DBConfig):
driver: str = "postgresql"
user: str = MISSING
port: int = 5432
password: str = MISSING
timeout: int = 10
class Config:
# Note the lack of defaults list here.
# In this example it comes from config.yaml
db: DBConfig = MISSING
cs = ConfigStore.instance()"config", node=Config)"db", name="mysql", node=MySQLConfig)"db", name="postgresql", node=PostGreSQLConfig)
# The config name matches both 'config.yaml' under the conf directory
# and 'config' stored in the ConfigStore.
# config.yaml will compose in db: mysql by default (per the defaults list),
# and it will be validated against the schema from the Config class
@hydra.main(config_path="conf", config_name="config")
def my_app(cfg: Config) -> None:

When db/mysql.yaml and db/postgresql.yaml are loaded, the corresponding configs from the ConfigStore are used automatically. This can be used to validate that both the configuration files (mysql.yaml and postgresql.yaml) and the command line overrides are conforming to the schema.

$ python db.port=fail
Error merging override db.port=fail
Value 'fail' could not be converted to Integer
full_key: db.port

Unlike the example in the previous page, the Defaults List here is config.yaml and not in the Config class.

- db: mysql
Last updated on by Omry Yadan