Transformers and Validators (WIP: needs more standard transformers validators)

Transformers and Validators

Inspired by Javax validators

Performance considerations:

Reflection is performed during the route build to create a list of transformers on the request payloads, at runtime the parameters are transformed by the built list of transformers.

Basic Example

(Transformers and validators can be applied to both Parameters and request Bodies)

@Request("Requests an invitation email")
data class EmailInvite(
    @LowerCase // Apply the lowercase transformer
    @Trim // Apply the trim transformer
    val email: String // The received email will be lowercase and trimmed
)

...
// Then just create a route like always
route("invite") {
    post<IDParam, EmailInviteResponse, EmailInvite, APIPrincipal> {params, invite ->
        respond(EmailInviteResponse(EmailService.sendSignatureInvitationEmail(invite, params.processID, principal()).await()))
    }
}

Creating a new Transformer/Validator

1. Create the Transformer Validator

@Retention(AnnotationRetention.RUNTIME)
@Target(AnnotationTarget.PROPERTY)
@ValidationAnnotation
annotation class LowerCase

object LowerCaseValidator: AValidator<String, LowerCase>(String::class, LowerCase::class) {
    override fun validate(subject: String?, annotation: LowerCase): String? {
        return subject?.toLowerCase() // Throw exception if the request is invalid, it will be caught by any appropriate exception handler that was declared on the route
    }
}

2. Register the package for the reflections library to find the Transformer/Validator

install(OpenAPIGen) {
    ...
    scanPackagesForModules += "com.example.validators"
}