Pass in the Entire Context to the Validator

[abhirathmahipal]

Current API

I've left some annotations in the code below, please read the comments as well :)

class ScoreValueValidator:
    """Validate the range of score value to be between 0.5 and 5"""

    
    def __call__(self, value):
        # value only contains the current field's value. 
        # How do we write validations which might require other fields as well?

        if value and not all(0 <= value <= 5 for value in value.values()):
            raise ValidationError("is invalid")


@domain.aggregate
class Assignment:
    competition_id = Identifier(required=True)
    group_id = Identifier(required=True)
    judge_id = Identifier(required=True)
    entry_id = Identifier(required=True)
    score = Dict(validators=[ScoreValueValidator()])

Suggested API

class ScoreValueValidator:
    """Validate the range of score value to be between 0.5 and 5"""

  
    def __call__(self, value, obj):
       # demonstrating validation using other fields
       if not obj.group_id:
            return

        if value and not all(0 <= value <= 5 for value in value.values()):
            raise ValidationError("is invalid")

The same should probably apply for Aggregates, Entities, Value Objects and Commands in my opinion.

[subhashb]

Since such a validation involves multiple fields, it is best placed at the model level. The object.clean() method is a good place for model-level field validations, along with in-built and custom field validators. Django adopts a similar validation technique.

As a contra, supporting access to other fields within validators will result in more complex code because:

• The validation is buried within a validator, so is easily missed when understangind the model and its invariants
• The element's structure is tightly coupled with the validator restricting its reusability

[abhirathmahipal]

@sagaragarwal94