Skip to content

API: Validation

ValidationResult

Dataclass representing the outcome of a single validation check.

from cascadeui import ValidationResult

result = ValidationResult(valid=True)
result = ValidationResult(valid=False, message="Must be at least 3 characters")
  • valid (bool): Whether the check passed
  • message (str): Error message (empty string if valid)

Validator Factories

Each returns a callable with signature (value, field, all_values) -> ValidationResult.

min_length(n, msg=None)

Value must have at least n characters.

max_length(n, msg=None)

Value must have at most n characters.

regex(pattern, msg=None)

Value must match the regex pattern.

choices(allowed, msg=None)

Value must be in the allowed list.

min_value(n, msg=None)

Numeric value must be at least n. Non-numeric values fail with a type error message.

max_value(n, msg=None)

Numeric value must be at most n. Non-numeric values fail with a type error message.

Runner Functions

validate_field(value, field_def, all_values)

Runs all validators for a single field definition.

  • value: The field's current value
  • field_def (dict): Must have a "validators" key with a list of callables
  • all_values (dict): All field values (for cross-field validation)

Returns: List[ValidationResult] of failed checks (empty if all pass).

validate_fields(values, field_defs)

Runs validators for all fields.

  • values (dict): Mapping of field_id -> value
  • field_defs (list[dict]): List of field definitions, each with "id" and optional "validators"

Returns: Dict[str, List[ValidationResult]] mapping field_id -> list of failures. Only fields with errors are included.

Custom Validators

Any callable with the signature (value, field, all_values) -> ValidationResult:

def no_spaces(value, field, all_values):
    if value and " " in str(value):
        return ValidationResult(False, "Must not contain spaces")
    return ValidationResult(True)

Async validators are also supported:

async def unique_name(value, field, all_values):
    exists = await db.check(value)
    return ValidationResult(not exists, "Already taken" if exists else "")