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Validator Signature Migration Guide

Overview

This guide helps you migrate your custom value object validators to the new signature introduced in sindripy v1.0.0. The change simplifies validator method signatures and reduces code repetition.

What Changed?

Before (Old Behavior):

  • Value was validated before being assigned to _value
  • Validators received the value as a parameter: method(self, value: T)
  • Value assignment happened only after all validators passed

After (New Behavior):

  • Value is assigned to _value first, then validated
  • Validators access the value directly via self._value: method(self)
  • Cleaner signatures, no repetitive parameter passing

Migration Benefits

✅ Cleaner Code: No need to pass value parameter to every validator
✅ Less Repetition: Eliminates repetitive parameter passing in complex validation chains
✅ Better Readability: Validators are more focused on their specific validation logic
✅ Maintained Safety: Validators still execute immediately after value assignment

Step-by-Step Migration

Step 1: Identify Validators to Update

Find all methods in your value objects decorated with @validate:

class YourValueObject(ValueObject[str]):
    @validate
    def _your_validator(self, value: str) -> None:  # OLD - needs update
        pass

Step 2: Update Method Signatures

Remove the value parameter from validator methods signatures:

Before: 

@validate
def _your_validator(self, value: str) -> None:
    if len(value) < 3:
        raise ValueError("Too short")
After: 
@validate
def _your_validator(self) -> None:
    if len(self._value) < 3:
        raise ValueError("Too short")

Step 3: Update Validation Logic

Replace all value references with self._value:

class ProductName(ValueObject[str]):
    @validate
    def _validate_not_empty(self) -> None:  # Changed signature
        if not self._value.strip():  # Changed from 'value'
            raise ValueError("Product name cannot be empty")

    @validate(order=2)
    def _validate_length(self) -> None:  # Changed signature
        if len(self._value) > 100:  # Changed from 'value'
            raise ValueError("Product name too long")

Complete Migration Examples

Example 1: Simple String Validation

Before: 

class Username(ValueObject[str]):
    @validate
    def _validate_not_empty(self, value: str) -> None:
        if not value.strip():
            raise ValueError("Username cannot be empty")

    @validate(order=1)
    def _validate_length(self, value: str) -> None:
        if len(value) < 3:
            raise ValueError("Username must be at least 3 characters")

After: 

class Username(ValueObject[str]):
    @validate
    def _validate_not_empty(self) -> None:
        if not self._value.strip():
            raise ValueError("Username cannot be empty")

    @validate(order=1)
    def _validate_length(self) -> None:
        if len(self._value) < 3:
            raise ValueError("Username must be at least 3 characters")

Example 2: Complex Validation with Order

Before: 

class Price(ValueObject[float]):
    @validate(order=1)
    def _validate_type(self, value: float) -> None:
        if not isinstance(value, (int, float)):
            raise InvalidTypeError("Price must be numeric")

    @validate(order=2)
    def _validate_positive(self, value: float) -> None:
        if value < 0:
            raise ValueError("Price cannot be negative")

    @validate(order=3)
    def _validate_precision(self, value: float) -> None:
        if abs(value - round(value, 2)) > 0.0001:
            raise ValueError("Price cannot have more than 2 decimal places")

After: 

class Price(ValueObject[float]):
    @validate(order=1)
    def _validate_type(self) -> None:
        if not isinstance(self._value, (int, float)):
            raise InvalidTypeError("Price must be numeric")

    @validate(order=2)
    def _validate_positive(self) -> None:
        if self._value < 0:
            raise ValueError("Price cannot be negative")

    @validate(order=3)
    def _validate_precision(self) -> None:
        if abs(self._value - round(self._value, 2)) > 0.0001:
            raise ValueError("Price cannot have more than 2 decimal places")

Example 3: Custom Exception Classes

Before: 

class NegativeAgeError(SindriValidationError):
    def __init__(self, value: int) -> None:
        super().__init__(f"Age cannot be negative, received {value}")

class Age(ValueObject[int]):
    @validate
    def _validate_positive(self, value: int) -> None:
        if value < 0:
            raise NegativeAgeError(value)

After: 

class NegativeAgeError(SindriValidationError):
    def __init__(self, value: int) -> None:
        super().__init__(f"Age cannot be negative, received {value}")

class Age(ValueObject[int]):
    @validate
    def _validate_positive(self) -> None:
        if self._value < 0:
            raise NegativeAgeError(self._value)

Need Help?

Backward Compatibility

For a transition period, sindripy provides an adapter that automatically detects and supports both old and new validator signatures. However, we recommend migrating to the new signature as soon as possible for cleaner code and future compatibility.