java - hibernate - 从多对多中删除

Question

我有以下两个 POJO:

@Entity(name = "project")
@Table(name = "project")
public class Project {
    @Column(name = "identifier")
    @Id
    @GeneratedValue
    private Integer identifier;

    @ManyToMany(cascade = CascadeType.ALL)
    private Set<Member> members = new HashSet<Member>();

    // --- constructors ---

    public Project() {
    }

    // --- getters ---

    public Integer getIdentifier() {
        return identifier;
    }

    public Set<Member> getMembers() {
        return members;
    }
}

和

@Entity(name = "member")
@Table(name = "member")
public class Member {
    @Column(name = "identifier")
    @Id
    @GeneratedValue
    private Integer identifier;

    @Column(name = "name", columnDefinition = "text")
    private String name;

    @ManyToMany(mappedBy = "members")
    private Set<Project> projects = new HashSet<Project>();

    // --- constructors ---

    public Member() {
    }

    // --- getters ---

    public Integer getIdentifier() {
        return identifier;
    }

    public String getName() {
        return name;
    }

    public Set<Project> getProjects() {
        return projects;
    }
}

从多对多关系中删除的常见做法是什么？以下代码可以完美运行，但会产生大量开销。首先，有一些疑问:

1. 1 个获取项目的查询，由 member.getProjects() 触发
2. N 个查询来获取每个项目的所有成员，由 project.getMembers() 触发

其次，获取项目(查询 1)和成员(查询 2)的完整数据集，而不仅仅是标识符。

final Member member = ...;
for (final Project project : member.getProjects()) {
    project.getMembers().remove(member);
}
db.delete(member);

是否可以在不被迫编写临时查询的情况下更有效地完成此操作？

Answer 1

看这里:

How to remove entity with ManyToMany relationship in JPA (and corresponding join table rows)?

此外，您还可以选择使用 jpql 语句来删除数据:

http://docs.oracle.com/html/E24396_01/ejb3_overview_query.html#ejb3_overview_query_delete

但我认为第一个链接就是您正在寻找的内容。