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Version: 1.1

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). To achieve this, we will follow the common pattern of Extending Configs - but instead of extending another config file, we will extend a Structured Config.

This page shows how to validate the config files config.yaml, db/mysql.yaml and db/postgresql.yaml against a Structured Config schema.

Validating against a schema in the same config group#

ย Example (Click Here)

Given the config directory structure:

conf/โ”œโ”€โ”€ config.yamlโ””โ”€โ”€ db    โ”œโ”€โ”€ mysql.yaml    โ””โ”€โ”€ postgresql.yaml

We will add Structured Config schema for each of the config files above and store in the Config Store as base_config, db/base_mysql and db/base_postgresql.

Then, we will use the Defaults List in each config to specify its base config as follows:

defaults:  - base_config  - db: mysql  # See composition order note  - _self_
debug: true
defaults:  - base_mysql
user: omrypassword: secret

defaults:  - base_postgresql
user: postgres_userpassword: drowssap

One difference in the source code is that we have removed the Defaults List from the Config dataclass. The primary Defaults List will come from config.yaml. (Click to expand)
@dataclassclass DBConfig:    driver: str = MISSING    host: str = "localhost"    port: int = MISSING
@dataclassclass MySQLConfig(DBConfig):    driver: str = "mysql"    port: int = 3306    user: str = MISSING    password: str = MISSING
@dataclassclass PostGreSQLConfig(DBConfig):    driver: str = "postgresql"    user: str = MISSING    port: int = 5432    password: str = MISSING    timeout: int = 10
@dataclassclass Config:    db: DBConfig = MISSING    debug: bool = False
cs = ConfigStore.instance()"base_config", node=Config)"db", name="base_mysql", node=MySQLConfig)"db", name="base_postgresql", node=PostGreSQLConfig)
@hydra.main(config_path="conf", config_name="config")def my_app(cfg: Config) -> None:    print(OmegaConf.to_yaml(cfg))
if __name__ == "__main__":    my_app()

When Hydra composes the final config object it will use the config schemas as specified in the Default Lists.
Like before, Hydra will catch user errors in the command line:

$ python db.port=failError merging override db.port=failValue 'fail' could not be converted to Integer        full_key: db.port        object_type=MySQLConfig
Use --info commands to see how a config was composed (Expand)
$ python --info defaults-tree
Defaults Tree*************<root>:  hydra/config:    hydra/output: default    hydra/launcher: basic    hydra/sweeper: basic    hydra/help: default    hydra/hydra_help: default    hydra/hydra_logging: default    hydra/job_logging: default    _self_  config:    base_config    db: mysql:      db/base_mysql      _self_    _self_
$ python --info defaults
Defaults List*************| Config path                 | Package             | _self_ | Parent       | ------------------------------------------------------------------------------| hydra/output/default        | hydra               | False  | hydra/config || hydra/launcher/basic        | hydra.launcher      | False  | hydra/config || hydra/sweeper/basic         | hydra.sweeper       | False  | hydra/config || hydra/help/default          |          | False  | hydra/config || hydra/hydra_help/default    | hydra.hydra_help    | False  | hydra/config || hydra/hydra_logging/default | hydra.hydra_logging | False  | hydra/config || hydra/job_logging/default   | hydra.job_logging   | False  | hydra/config || hydra/config                | hydra               | True   | <root>       || base_config                 |                     | False  | config       || db/base_mysql               | db                  | False  | db/mysql     || db/mysql                    | db                  | True   | config       || config                      |                     | True   | <root>       |------------------------------------------------------------------------------

Validating against a schema from a different config group#

ย Example (Click Here)

In the above example, the schema we used was stored in the same config group. This is not always the case, for example - A library might provide schemas in its own config group.

Here is a modified version of the example above, where a mock database_lib is providing the schemas we want to validate against.
import database_lib

@dataclassclass Config:    db: database_lib.DBConfig = MISSING    debug: bool = False
cs = ConfigStore.instance()"base_config", node=Config)
# database_lib registers its configs# in database_lib/dbdatabase_lib.register_configs()

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

if __name__ == "__main__":    my_app()
@dataclassclass DBConfig:  ...
@dataclassclass MySQLConfig(DBConfig):  ...
@dataclassclass PostGreSQLConfig(DBConfig):  ...

def register_configs() -> None:    cs = ConfigStore.instance()        group="database_lib/db",        name="mysql",        node=MySQLConfig,    )        group="database_lib/db",        name="postgresql",        node=PostGreSQLConfig,    )

The Defaults List entry for the base config is slightly different:

defaults:  - /database_lib/db/[email protected]_here_
user: omrypassword: secret
defaults:  - /database_lib/db/[email protected]_here_  # See composition order note    - _self_
user: postgres_userpassword: drowssap
  • We refer to the config with an absolute path because it is outside the subtree of the db config group.
  • we override the package to _here_ to ensure that the package of the schema is the same as the package of the config it's validating.

A Note about composition order#

By default, Hydra 1.1 appends _self_ to the end of the Defaults List. This behavior is new in Hydra 1.1 and different from previous Hydra versions. As such Hydra 1.1 issues a warning if _self_ is not specified in the primary config, asking you to add _self_ and thus indicate the desired composition order. To address the warning while maintaining the new behavior, append _self_ to the end of the Defaults List. Note that in some cases it may instead be desirable to add _self_ directly after the schema and before other Defaults List elements.

See Compositon Order for more information.