Validated上有一个示例,它显示了我们可以组合验证失败的情况。
对于您的情况(我将在这里假设一些事情,例如书中可用的字段),我想它看起来像:
data class Book(val title: String, val authorName: String, val pageCount: Int)
在这里,我们使用 Semigroup 的定义创建错误:
sealed class BookValidationError {
data class PropertyNotChanged(val propertyName: String) : BookValidationError()
data class Multiple(val errors: Nel<BookValidationError>) : BookValidationError()
}
object BookValidationErrorSemigroup : Semigroup<BookValidationError> {
override fun BookValidationError.combine(b: BookValidationError): BookValidationError = when {
this is Multiple && b is Multiple -> Multiple(errors + b.errors)
this is Multiple && b !is Multiple -> Multiple(errors + b)
this !is Multiple && b is Multiple -> Multiple(this.nel() + b.errors)
else -> BookValidationError.Multiple(NonEmptyList(this, b))
}
}
然后我们可以ApplicativeError
为错误类型定义相关的:
private val bookApplicativeError : ApplicativeError<ValidatedPartialOf<BookValidationError>, BookValidationError> =
Validated.applicativeError(BookValidationErrorSemigroup)
我们将它与一个辅助类结合在一起:
class BookValidation(
private val book: Book
) : ApplicativeError<ValidatedPartialOf<BookValidationError>, BookValidationError> by bookApplicativeError {
fun <T> fieldIsNot(name: String, actualValue: T, incorrectValue: T): Kind<ValidatedPartialOf<BookValidationError>, Book> =
if(actualValue == incorrectValue) raiseError(BookValidationError.PropertyNotChanged(name))
else just(book)
}
和一个易于访问的扩展功能:
fun Book.validateThat(titleIsNot : String, authorNameIsNot: String, pageCountIsNot: Int) =
with(BookValidation(this)) {
map(
fieldIsNot("title", title, titleIsNot),
fieldIsNot("authorName", authorName, authorNameIsNot),
fieldIsNot("pageCount", pageCount, pageCountIsNot)
) { this@validateThat }.handleErrorWith {
raiseError(it)
}
}
然后,如果你像这样执行它:
fun main() {
Book("a", "b", 123).validateThat(
titleIsNot = "c",
authorNameIsNot = "d",
pageCountIsNot = 124
).let(::println)
Book("a", "b", 123).validateThat(
titleIsNot = "a",
authorNameIsNot = "b",
pageCountIsNot = 123
).let(::println)
Book("a", "b", 123).validateThat(
titleIsNot = "c",
authorNameIsNot = "b",
pageCountIsNot = 124
).let(::println)
}
第一个将有效,输出如下:
Valid(a=Book(title=a, authorName=b, pageCount=123))
但是第二个会输出:
Invalid(e=Multiple(errors=NonEmptyList(all=[PropertyNotChanged(propertyName=pageCount), PropertyNotChanged(propertyName=title), PropertyNotChanged(propertyName=authorName)])))
在这个Invalid
实例内部,我们有一个 NonEmptyList,其中包含所有未通过验证的字段。如果我们重新格式化输出,我们可以看到它们:
Invalid(e=Multiple(
errors=NonEmptyList(all=[
PropertyNotChanged(propertyName=pageCount),
PropertyNotChanged(propertyName=title),
PropertyNotChanged(propertyName=authorName)
])
))
现在,对于第三种情况,由于其中只有一个保持不变,我们得到以下输出:
Invalid(e=PropertyNotChanged(propertyName=authorName))