[英]How to validate single element in Future[List[T]] to return Future[List[T]] or throw exception
No need to pay attention to the purpose of the function here, it's only for demonstration: 此处无需注意功能的用途,仅用于演示:
def readAllByPersonOrFail(person: Person, otherPersonId: Long): Future[List[Person]] = {
val personSiblingsFuture: Future[List[Person]] = personSiblingsDomain.readAllByPersonId(person.id)
personSiblingsFuture.map { persons =>
persons.find(_.id == otherPersonId) match {
case Some(person) =>
person.isActive match {
case true => person
case false => throw new IllegalArgumentException("something inactive")
}
case None => throw new IllegalArgumentException("something wrong ehre")
}
}
personSiblingsFuture
}
I would like to return personSiblingsFuture above iff it validates (makes sure correct person is in the list and is active), otherwise throw the exception. 如果验证,我想返回上面的personSiblingsFuture(确保正确的人在列表中并且处于活动状态),否则抛出异常。 I don't think the above code is doing the right thing as it is not existing upon failure. 我不认为上面的代码做对了,因为失败后就不存在了。
Take a look at scala.concurrent.Future.map
. 看一下scala.concurrent.Future.map
。 This creates a new future, whose value is resolved by applying a function to the successful result of this future. 这将创建一个新的未来,其价值可以通过将函数应用于该未来的成功结果来解决。
Note that here you're throwing away the resulting future you just created with .map()
too. 请注意,这里您还将丢弃刚刚使用.map()
创建的结果。
There are a few areas to solve your problem, though you should question more deeply the use of exceptions with Futures
. 尽管您应该更深地质疑Futures
中异常的使用,但仍有一些地方可以解决您的问题。 Scala provides concepts like Future
, Option
, and Try
specifically to avoid throwing exceptions and have a clearer control flow. Scala提供了诸如Future
, Option
和Try
类的概念,专门用于避免引发异常并具有更清晰的控制流程。
In your funciton, 在您的功能中
def func(...): Future[List[Person]] {
val personSiblingsFuture = ...;
personSiblingsFuture.map { persons =>
...
}
}
// note we're not returning personSiblingsFuture,
// but the mapped result
When someone actually tries to get the value of the future, eg by using .value
, they might see an exception intead: 当某人实际上尝试获取未来的价值时,例如通过使用.value
,他们可能会看到一个异常提示:
def main() {
val future = func(...); // this is fine
val my_list = future.value; // awaits Future, might throw here
}
Returning a future that might throw is strange, it might be a bit easier if the you actually explicitly a had a function that might throw, eg 返回一个可能抛出的未来很奇怪,如果您实际上明确地拥有一个可能抛出的函数,则可能会容易一些。
/** jsdoc describing function **/
def funcMightThrow(...): List[Person] {
val personSiblingsFuture = ...;
val personSiblings = personSiblingsFuture.value;
personSiblings.find(_.id == otherPersonId) match {
case Some(person) =>
person.isActive match {
case true => personSiblings
case false => throw new IllegalArgumentException("something inactive")
}
case None => throw new IllegalArgumentException("something wrong ehre")
}
}
def func(...): Future[Try[List[Person]]] {
val personSiblingsFuture = ...;
personSiblingsFuture.map { persons =>
...
// successful case returns 'persons' (List[Person])
// fail cases return Failure(...) instead
}
} // return the mapped future
You can also return Try[List[Person]]
rather than a Future[]
of that, by using .value
, which makes func
a blocking function. 您也可以使用.value
返回Try[List[Person]]
而不是其中的Future[]
,这会使func
成为阻塞函数。
声明:本站的技术帖子网页,遵循CC BY-SA 4.0协议,如果您需要转载,请注明本站网址或者原文地址。任何问题请咨询:yoyou2525@163.com.