Validators¶

Concrete ValidationRule implementations for common input constraints. Each validator is a stateless, reusable rule that returns RuleViolationError instances when the input fails its constraint.

RequiredValidator¶

Fails when the value is None or an empty string. Useful for mandatory form fields, API parameters, and command properties.

RequiredValidator("username").validate(None)     # -> [RuleViolationError]
RequiredValidator("username").validate("Alice")  # -> []

EmailValidator¶

Validates that a string value matches a basic RFC-compatible email pattern. Suitable for client-side and API-level validation — does not check deliverability.

EmailValidator("email").validate("user@example.com")  # -> []
EmailValidator("email").validate("not-an-email")      # -> [RuleViolationError]

LengthValidator¶

Validates that a string's length falls within a [minimum_length, maximum_length] range. Both bounds are inclusive and optional — omit a bound to leave it unconstrained.

LengthValidator("password", minimum_length=8, maximum_length=128).validate("short")  # -> [RuleViolationError]
LengthValidator("password", minimum_length=8).validate("0" * 10)                      # -> []

RangeValidator¶

Validates that a numeric value (integer or float) falls within a [minimum_value, maximum_value] range. Both bounds are inclusive and optional.

RangeValidator("age", minimum_value=0, maximum_value=150).validate(-5)  # -> [RuleViolationError]
RangeValidator("age", minimum_value=0).validate(30)                     # -> []

CompositeValidationRule¶

Combines multiple validators into a single rule. Evaluates every rule and returns all errors — there is no short-circuit. Every violation is reported.

composite = CompositeValidationRule([
    RequiredValidator("email"),
    EmailValidator("email"),
])
composite.validate("bad")  # -> [RuleViolationError for invalid_email]

When to use¶

Use individual validators for single-field checks in commands, queries, and API input. Compose them with CompositeValidationRule when multiple constraints apply to the same field or when several fields must be validated together. All validators use the foundation RuleViolationError type with ErrorMetadata carrying field and error-code context.