Question

我有两个关系ManyToMany的类，我想创建Audiences，然后将它们添加到事件中，但它会抛出“分离”异常。

class Event {
    @ManyToMany(
            fetch = FetchType.LAZY,
            targetEntity = Audience.class,
            cascade = {CascadeType.PERSIST, CascadeType.MERGE})
    @JoinTable(name = "UC_EVENT_AUDIENCE",
            joinColumns = @JoinColumn(name = "event_id"),
            inverseJoinColumns = @JoinColumn(name = "audience_id"))    
    private List<Audience> targetAudiences = new ArrayList<>();
}

clsas Audience {
    @ManyToMany(fetch = FetchType.LAZY, mappedBy = "targetAudiences")
    private List<Event> events = new ArrayList<>();
}

public void run(ApplicationArguments args) throws Exception {
    //Generate audience data
    List<Audience> audiences = dataGenerator.createAudiences();
    //Save to db
    audienceRepository.save(audiences);

    Event event = new Event();
    event.setTargetAudiences(audiences);    
    eventRepository.save(events);
}

Answer 1

您正在首先保存受众群体，但是在您的代码中定义了关系：

活动将因此而处理受众的持久性：

 @ManyToMany(
            fetch = FetchType.LAZY,
            targetEntity = Audience.class,
            cascade = {CascadeType.PERSIST, CascadeType.MERGE})

首先创建受众，然后创建事件，然后将受众列表附加到事件，并将事件对象最终保存到数据库。

Answer 2

作为一种变体，您可以使用这种'PrePersist'util方法来“链接”事件和受众：

@Entity
public class Event {

    @ManyToMany(cascade = {CascadeType.PERSIST, CascadeType.MERGE})
    private final Set<Audience> audiences = new HashSet<>();

    @PrePersist
    public void addAudiences() {
        audiences.forEach(audience -> audience.getEvents().add(this));
    }
}

@Entity
public class Audience {

    @ManyToMany(mappedBy = "audiences")
    private final Set<Event> events = new HashSet<>();

    //...
    public Set<Event> getEvents() {
        return events;
    }
}

有关ManyToMany关联和'实用工具方法'的更多信息：Hibernate User Guide

我的example和tests。

Answer 3

我这样做了，它为我工作：

public class Event {

    @ManyToMany(fetch = FetchType.EAGER)
    @JoinTable(name = "event_audience",
            joinColumns = @JoinColumn(name = "event_id"),
            inverseJoinColumns = @JoinColumn(name = "audience_id"),
            uniqueConstraints = @UniqueConstraint(columnNames = {"event_id", "audience_id"}))
    private List<Audience> audiences = new ArrayList<>();
}

public class Audience {

    @Column(name = "audience_name", nullable = false, unique = true)
    private String name;
}

此外，我还有两个用于保存Audience和Events的存储库，用于扩展spring的JpaRepository。

现在我可以像这样创建受众：

audienceRepository.save(new Audience("Name"));

并将它们添加到我的活动中：

Event eventFirst = new Event();
eventFirst.getAudiences().add(audiences.get(0));
eventRepository.save(eventFirst);

Hibernate ManyToMany保存

3 个答案: