我都有一个电子邮件列表,对于每个电子邮件,我将在电子邮件表中查找它,以查看该电子邮件是否存在。如果这样做,什么也不做,我会丢下错误。这是我的代码;
def lookupEmailStatus(email: EmailAddress, requestId: RequestId)(
implicit ec: ExecutionContext): HttpServiceResult[List[EmailStatusDTO]] = {
emailDatabase
.getEmailStatusByEmail(email, requestId)
.map(
l =>
if (l.isEmpty) {
logger.error(
LoggingMessage(
requestId,
s"Email status not found by ${email.email} failed"))
EntityNotFound(s"${email.email}", requestId)
} else {
l
}
)
.leftMap[HttpError] {
case e =>
logger.error(
LoggingMessage(
requestId,
s"Retrieve email status by ${email.email} failed"))
DatabaseError(e.message, requestId)
}
}
我运行代码时会出现错误:
Error:(57, 27) type mismatch;
found : cats.data.EitherT[model.HttpError,Product with Serializable]
required: model.HttpServiceResult[List[EmailStatusDTO]]
(which expands to) cats.data.EitherT[model.HttpError,List[EmailStatusDTO]]
.leftMap[HttpError] {
如果我删除了.map(..)方法,它可以正常工作,但这不是我想要的:
def lookupEmailStatus(email: EmailAddress, requestId: RequestId)(
implicit ec: ExecutionContext): HttpServiceResult[List[EmailStatusDTO]] = {
emailDatabase
.getEmailStatusByEmail(email, requestId)
.leftMap[HttpError] {
case e =>
logger.error(
LoggingMessage(
requestId,
s"Retrieve email status by ${email.email} failed"))
DatabaseError(e.message, requestId)
}
}
这是类型定义:
type HttpServiceResult[A] = ServiceResult[HttpError, A]
type ServiceResult[Err, A] = EitherT[Future, Err, A]
如果if
的一个分支返回列表,而另一个分支将返回错误,则if
完全返回Product with Serializable
。
尝试用flatMap
替换map
,并用EitherT
def lookupEmailStatus(email: EmailAddress, requestId: RequestId)(
implicit ec: ExecutionContext): HttpServiceResult[List[EmailStatusDTO]] =
emailDatabase
.getEmailStatusByEmail(email, requestId)
.leftMap[HttpError] {
case e =>
logger.error(
LoggingMessage(
requestId,
s"Retrieve email status by ${email.email} failed"))
DatabaseError(e.message, requestId)
}.flatMap[HttpError, List[EmailStatusDTO]](
/*(*/l/*: List[EmailStatusDTO])*/ =>
if (l.isEmpty) {
logger.error(
LoggingMessage(
requestId,
s"Email status not found by ${email.email} failed"))
EitherT.leftT/*[Future, List[EmailStatusDTO]]*/(EntityNotFound(s"${email.email}", requestId))
} else {
EitherT.rightT/*[Future, HttpError]*/(l)
}
)
如已经提到的 @dmytro-mitin,问题的根本原因是您在条件的两个分支中都没有返回相同的类型。解决的一种方法是确保您返回正确的类型。
我认为,更好的方法是将cats.data.EitherT.ensure
用于list.isEmpty
检查。这样,您就会明确您关心的内容(即,如果列表为空,返回错误),而不必手动处理快乐案件。
您的代码将变成:
def lookupEmailStatus(email: EmailAddress, requestId: RequestId)(
implicit ec: ExecutionContext): HttpServiceResult[List[EmailStatusDTO]] = {
emailDatabase
.getEmailStatusByEmail(email, requestId)
.ensure({
logger.error(LoggingMessage(requestId, s"Email status not found by ${email.email} failed"))}
EntityNotFound(s"${email.email}", requestId)
})(!_.isEmpty)
.leftMap[HttpError] {
case e =>
logger.error(
LoggingMessage(
requestId,
s"Retrieve email status by ${email.email} failed"))
DatabaseError(e.message, requestId)
}
}