Question

我有一个简单的@ManyToMany关系我想要捕获，但我一直遇到无限循环问题。

我有三个类如下：Person，Issue，IssuePosition

每个人都可以对任何问题持有立场，并且可以针对不同的问题采取立场。职位是“为”“反对”“中立”

问题是“增税”“建立新学校”等问题

现在我进入了Person类：

@OneToMany(cascade = CascadeType.ALL, orphanRemoval = true, mappedBy = "person", fetch = FetchType.EAGER)
@Fetch(FetchMode.SUBSELECT)
    private List<IssuePosition> issuePositions  = new ArrayList<IssuePosition>();

并在问题类中：

@OneToMany(cascade = CascadeType.ALL, orphanRemoval = true, mappedBy = "issue", fetch = FetchType.EAGER)
    private List<IssuePosition> issuePositions  = new ArrayList<IssuePosition>();

在IssuePosition类中的

：

@ManyToOne(optional = true)
private Issue   issue;

@ManyToOne(optional = true)
private Person  person;

这会导致调用加载Person以加载IssuePositions，后者会加载载入载有Person的IssuePositions的问题。

如何阻止这种情况？我删除了fetch = FetchType.EAGER，但没有帮助

Answer 1

This教程提供了一个很好的示例，说明如何使用@ManyToMany注释来使用@JoinTable来映射关系。 Here's一个稍微复杂的例子。

Answer 2

我尝试了你的实现，它运行正常我有以下内容。

@Entity
public class IssuePosition {

    @Id
    private int id;

    @ManyToOne(optional = true)
    private Issue   issue;

    @ManyToOne(optional = true)
    private Person  person;

    @Override
    public String toString() {
        return "IssuePosition [id=" + id + "]";
    }

}



@Entity
public class Person {

    @Id
    private int id;

    @OneToMany(cascade = CascadeType.ALL, orphanRemoval = true, mappedBy = "person", fetch = FetchType.EAGER)
    @Fetch(FetchMode.SUBSELECT)
    private List<IssuePosition> issuePositions  = new ArrayList<IssuePosition>();

    @Override
    public String toString() {
        return "Person [id=" + id + ", issuePositions=" + issuePositions + "]";
    }


}


@Entity
public class Issue {

    @Id
    private int id;

    @OneToMany(cascade = CascadeType.ALL, orphanRemoval = true, mappedBy = "issue", fetch = FetchType.EAGER)
    private List<IssuePosition> issuePositions  = new ArrayList<IssuePosition>();

    @Override
    public String toString() {
        return "Issue [id=" + id + ", issuePositions=" + issuePositions + "]";
    }


}

当我尝试这个时：

EntityManagerFactory emf = Persistence.createEntityManagerFactory("jpaQuery");
        EntityManager em = emf.createEntityManager();

        Person p = em.find(Person.class, 1);
        System.out.println(p);

我获得了这个

Hibernate：从Person person0_ where中选择person0_.id作为id1_2_0_ person0_.id =？ Hibernate：选择issueposit0_.person_id as person3_2_2_，issueposit0_.id为id1_1_2_，issueposit0_.id为 id1_1_1_，issueposit0_.issue_id为issue2_1_1_，issueposit0_.person_id as person3_1_1_，issue1_.id为IssuePosition的id1_0_0_ issueposit0_ left outer join Issue issue1_ on issueposit0_.issue_id = issue1_.id其中issueposit0_.person_id =？ Hibernate：选择issueposit0_.issue_id作为issue2_0_2_， issueposit0_.id为id1_1_2_，issueposit0_.id为id1_1_1_， issueposit0_.issue_id为issue2_1_1_，issueposit0_.person_id as person3_1_1_，person1_.id，来自IssuePosition issueposit0_的id1_2_0_ left outer join person person__ on issueposit0_.person_id = person1_.id issueposit0_.issue_id =？ Hibernate：选择issueposit0_.issue_id 如issue2_0_2_，issueposit0_.id为id1_1_2_，issueposit0_.id为 id1_1_1_，issueposit0_.issue_id为issue2_1_1_，issueposit0_.person_id 作为person3_1_1_，person1_.id为来自IssuePosition的id1_2_0_ issueposit0_ left outer join Person person1_ on issueposit0_.person_id = person1_.id其中issueposit0_.issue_id =？ Hibernate：选择issueposit0_.issue_id作为issue2_0_2_， issueposit0_.id为id1_1_2_，issueposit0_.id为id1_1_1_， issueposit0_.issue_id为issue2_1_1_，issueposit0_.person_id as person3_1_1_，person1_.id，来自IssuePosition issueposit0_的id1_2_0_ left outer join person person__ on issueposit0_.person_id = person1_.id issueposit0_.issue_id =？ Hibernate：选择issueposit0_.person_id as person3_2_2_，issueposit0_.id为id1_1_2_，issueposit0_.id as id1_1_1_，issueposit0_.issue_id为issue2_1_1_，issueposit0_.person_id as person3_1_1_，issue1_.id为IssuePosition的id1_0_0_ issueposit0_ left outer join Issue issue1_ on issueposit0_.issue_id = issue1_.id其中，issueposit0_.person_id在（从IssuePosition issueposit0_ left outer join中选择person1_.id 在personposit0_.person_id = person1_.id所在的人person1_ issueposit0_.issue_id =？）

人[id = 1，issuePositions = [IssuePosition [id = 1，issue = Issue [id = 1]]，IssuePosition [id = 2，issue = Issue [id = 2]]，IssuePosition [id = 3，issue = Issue [id = 3]]]]

似乎工作正常，你是否使用getter或setter打印东西，这可能会使进程无限循环。检查toString或任何其他方法是否不启动进程来进行循环。

Image

Spring Roo避免ManyToMany周期

2 个答案: