Customizing Value Objects

To create domain-specific value objects, extend one of the primitive base classes and add custom validation methods decorated with @validate. The validation methods are executed in the order they are defined in the class or by the order you specify using the order parameter in the @validate decorator.

Creating Value Objects through Subclassing

The main goal for creating custom value objects is to encapsulate domain-specific validation logic and express the ubiquitous language of your domain.

The fastest way to create these types of value objects is by subclassing one of the built-in primitive types.

from sindripy.value_objects import String


class ProductCode(String):
    ...

With no additional logic, the ProductCode class behaves exactly like a String value object but expresses the ubiquitous language of the domain better.

You can also specialize a value object and add custom validation logic using the @validate decorator as seen in the previous section

from sindripy.value_objects import Integer, validate, SindriValidationError


class NegativeIntegerError(SindriValidationError):
    def __init__(self) -> None:
        super().__init__("The integer must be positive")


class PositiveInteger(Integer):
    @validate
    def _must_be_positive(self):
        if self.value <= 0:
            raise NegativeIntegerError

Creating Own Value Objects from Scratch

If you find yourself needing a value object that is not implemented as a built-in primitives type, you can create your own value object from scratch by subclassing the ValueObject base class.

from datetime import date
from sindripy.value_objects import ValueObject, validate, SindriValidationError


class Date(ValueObject[date]):
    @validate
    def _must_be_a_date(self):
        if not isinstance(self.value, date):
            raise SindriValidationError("The value must be a date")