Derives: Validation (Reference)

This page documents Validate for models.

See also:

• Derives & traits
• Error handling

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Validate (models only)

• Derive: @derive(Validate)
• Requirement: a validate(self) -> Result[Self, E] method must exist on the model
• API: TypeName.new(...) -> Result[TypeName, E]

Rule:

• If a model derives Validate, you must construct it via TypeName.new(...) (validated construction). Raw construction via TypeName(...) is a compile-time error.

Semantics:

• TypeName.new(...) constructs the model, then calls validate(self).

Example

@derive(Validate)
model EmailUser:
    email: str
    is_active: bool = true

    def validate(self) -> Result[EmailUser, str]:
        if "@" not in self.email:
            return Err("invalid email")
        return Ok(self)

def make_user(email: str) -> Result[EmailUser, str]:
    # Validated construction (required for @derive(Validate))
    return EmailUser.new(email=email)

Defaults and parameters

TypeName.new(...) is generated from the model’s required fields (fields without defaults). Fields with defaults use their declared default values.

Additional constructors can be expressed as helper functions or associated functions on the model.