Exceptions

At the edge of your system, a request is either valid or rejected. validateOrThrow() returns nothing when every rule holds, and throws a ValidationException that carries the violations when any is broken:

suspend fun register(account: Account) {
    account.validateOrThrow()       // throws when a rule is broken
    accounts.save(account)          // only runs for a valid account
}

`ValidationException`

ValidationException is a RuntimeException, so it needs no throws declaration and passes through any layer. It has:

violations, the same list validate() returns, in the same order;
a message that lists each violation as path: message, joined by commas.

io.github.soleworks.validity.ValidationException: username: must have between 3 and 20 characters, username: must contain only letters or digits, password: must have at least 8 characters, password: must contain a digit

One handler for every request

Because every invalid object throws the same exception with the same data, one error handler turns all of them into the same response. With Ktor’s StatusPages, for example:

install(StatusPages) {
    exception<ValidationException> { call, error ->
        call.respond(
            HttpStatusCode.UnprocessableEntity,
            error.violations.map { mapOf("path" to it.path, "code" to it.code, "message" to it.message) }
        )
    }
}

A Spring @ExceptionHandler(ValidationException::class) does the same.

Every way to throw

Entry	Suspending	Blocking
`Validatable`	`validateOrThrow()`	`validateOrThrowBlocking()`
`ContextualValidatable<C>`	`validateOrThrow(context)`	`validateOrThrowBlocking(context)`
A `ValidationResult` you already have	`result.orThrow()`

validateOrThrow() is exactly validate().orThrow(): the same rules, the same violations.

Validation<T>, the rules beside a class, returns a result: call rules.validate(value).orThrow() to throw from it.

Get started

Writing rules

Beyond the object

Reading the result

Configuration

For AI agents

`ValidationException`

One handler for every request

Every way to throw

​ValidationException

​One handler for every request

​Every way to throw

`ValidationException`

One handler for every request

Every way to throw