field_serializer

Decorator that enables custom field serialization.

def field_serializer(
    field: str,
    *fields: str,
    mode: Literal['plain', 'wrap'] = 'plain',
    return_type: Any = PydanticUndefined,
    when_used: WhenUsed = 'always',
    check_fields: bool | None = None
) - > Callable

Decorator that enables custom field serialization. Use this to define how specific model fields should be converted during serialization, such as transforming a set into a sorted list.

Parameters

Name	Type	Description
field	str	The first field name the serializer should apply to; must be a string.
*fields	str	Additional field names the serializer should apply to.
mode	Literal['plain', 'wrap'] = 'plain'	The serialization mode: 'plain' replaces default logic entirely, while 'wrap' provides a handler to optionally invoke default serialization.
return_type	Any = PydanticUndefined	Optional return type for the function; if omitted, it is inferred from the decorated function's type annotation.
when_used	WhenUsed = 'always'	Determines the conditions under which the serializer is active (e.g., always, only for JSON, or only for Python objects).
check_fields	`bool	None` = None

Returns

Type	Description
Callable	A decorator function that wraps the serializer method and registers it with the Pydantic model's serialization logic.