Return default values of submodel

[mguyard]

Hello,

I don't find how i can retreive default value of a submodel in case of my parent model is empty.
In my project, i use Pydantic for parsing/validate a configuration.

My Configuration :

...
  config:
    common:
      position:
          # opened: 100 # Default : 100% 
          # closed: 0 # Default : 0%
          # min_ratio_change: 5 # Default : 5%
          # min_time_change: 10 # Default : 10 minutes
      temperature:
          outdoor_sensor: "sensor.outdoor_sensor_temperature"
          indoor_sensor: "sensor.smoke_sensor_palier_air_temperature"
...

In this situation, only the key position is set (all content of position is commented).

My code :

class PositionConfig(BaseModel):
    opened: int = Field(ge=0, le=100, default=100)
    closed: int = Field(ge=0, le=100, default=0)
    min_ratio_change: int = Field(ge=0, le=100, default=5)
    min_time_change: PositiveInt = Field(ge=1, default=10)

class CommonConfig(BaseModel):
    position: PositionConfig = PositionConfig()
    temperature: TemperatureConfig
    lux: LuxConfig | None = None
    manual: ManualConfig
    opening: OpeningConfig
    closing: ClosingConfig

I want when i'm in this situation (None in position), use all default values of PositionConfig.
After multiple research, i've add a default value for also position :

position: PositionConfig = PositionConfig()

But i've still this error :

2024-04-21 12:09:14.459952 ERROR CoversManager: 1 validation error for Config
common.position
Input should be a valid dictionary or instance of PositionConfig [type=model_type, input_value=None, input_type=NoneType]
For further information visit https://errors.pydantic.dev/2.7/v/model_type

If i comment position key in my configuration, this works and all default values are used but i want to manage the case of users forget to comment the position key.

If someone can help me to understand my error, this will be very appreciated.
Thank you

[samuelcolvin]

Yes, because your passing none to that field.

You need a field validator to return an instance of position in the case of none.

[mguyard]

Thanks.
Do you have a example ? I only use pydantic since 2 days and I don't yet understand everything.

Is it the usage of validate_default ?
Thanks

[samuelcolvin]

I'm afk, search for field_validator.

[mguyard]

Thank you.
It's work with this :

class CommonConfig(BaseModel):
    position: PositionConfig = PositionConfig()
    opening: OpeningConfig
    closing: ClosingConfig
    adaptive: bool = False
    manual: ManualConfig
    temperature: TemperatureConfig
    lux: LuxConfig | None = None

    @field_validator('position', mode='before')
    def position_none_default_values(cls, value):
        if value is None:
            return PositionConfig()
        return value