Java 8 Stream-如何从子级找到父级实体? [英] Java 8 stream - how to find parent entity from child?

问题描述

我的情况类似于:

public class A {
    private String id;
    @ManyToMany
    private Set<B> bSet;
    // getters and setters
}

和

public class B {
    private String id;
    // other attributes
    // getters and setters
}

当使用stream() API拥有B的实例时，如何找到A的实例?我正在尝试类似的东西:

How can I find an instance of A when I have an instance of B using the stream() API? I was trying something like:

public A findAFromB(B b) {
    List<A> aList = aService.findAll();
    Optional<A> matchingObject = aList.stream().filter({find a where a.getBSet().contains(b)}).getA();
return (A) matchingObject.get();
}

如何正确编写此过滤器?

How to properly write this filter?

推荐答案

类似使用findFirst或findAny作为终端操作的事情:

Soemthing like using a findFirst or findAny as a terminal operation:

Optional<A> matchingObject = aList.stream()
        .filter(a -> a.getbSet().contains(b))
        .findFirst();

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