时间戳

首页 > 解决方案 > Hibernate @ManyToMany 不使用 joinTable 并产生笛卡尔而不是内部连接

java - Hibernate @ManyToMany 不使用 joinTable 并产生笛卡尔而不是内部连接

问题描述

同事们，当关系@ManyToMany 时，您能否就 Hibernate 问题向我提出建议。项目实体：

    @Entity
    @Table(name = "PROJECT")
    @NamedQueries( {
        @NamedQuery(name = "Projects.employeesByExternal", query = "SELECT P FROM Project P INNER JOIN Employee E ON E.external=:external" )
    } )
    public class Project extends AbstractIdentified
    {
        @Column(name = "NAME") private String name;
        @Column(name = "EXT") private Boolean external;

        @ManyToMany
        @JoinTable( name = "EMPLOYEE_PROJECTS",
        joinColumns = { @JoinColumn(name = "PROJECT_ID") },
        inverseJoinColumns = { @JoinColumn(name = "EMPLOYEE_ID") } )
        private Set<Employee> employees;
    ... 
    // getters/setters here
    }

员工实体：

    @Entity
    @Table(name = "EMPLOYEE")
    public class Employee extends AbstractIdentified
    {
        @ManyToMany(mappedBy = "employees")
        private Set<Project> projects;
        ....
        // other fields and getters/setters here
    }

当应用程序启动时，它运行 init.sql：

insert into employee (id,status,ext) values (1,'CORP',true);
insert into employee (id,status,ext) values (2,'CORP',false);
insert into employee (id,status,ext) values (3, 'EXT',true);
insert into project (id,name) values (1,'project1');
insert into project (id,name) values (2,'project2');
insert into project (id,name) values (3,'project3');
insert into employee_projects (employee_id, project_id) values (1,1);
insert into employee_projects (employee_id, project_id) values (2,2);
insert into employee_projects (employee_id, project_id) values (3,3);

在 DAO 中，我准备了 DAO 方法来选择员工（至少一个）具有 external=false 的项目：

public List<Project> getProjectsByExternal( boolean isExternal )
{
    TypedQuery<Project> typedQuery = entityManager.createNamedQuery( "Projects.employeesByExternal", Project.class );
    typedQuery.setParameter( "external", isExternal );
    return typedQuery.getResultList();
}

现在我调用如下方法：

List<Project> list = projectDao.getProjectsByExternal(false);

我希望只得到一个 Project#2{name='project2'}，但结果是 3 个项目：

01:03:49 INFO  vez.Starter - Project#1{name='project1'}
01:03:49 INFO  vez.Starter - Project#2{name='project2'}
01:03:49 INFO  vez.Starter - Project#3{name='project3'}

当我检查 Hibernate 生成的 SQL（属性 hibernate.show_sql = true）时，我注意到 Hibernate 创建连接表“PROJECT”和“EMPLOYEE”而不使用中间表“EMPLOYEE_PROJECTS”（参见项目类中的注释@JoinTable）。有生成的SQL：

01:03:49 DEBUG org.hibernate.SQL - 
    select
        project0_.ID as ID1_3_,
        project0_.NAME as NAME2_3_ 
    from
        PROJECT project0_ 
    inner join
        EMPLOYEE employee1_ 
            on ( employee1_.EXT=?)

实际上，这意味着已为所有项目选择并乘以一名员工。我很困惑，因为这是我所期望的笛卡尔而不是内部连接。请指教我做错了什么？如何使用 NativeQuery 仅选择一个/多个员工具有外部属性 value=false 的项目？pom.xml：

<spring.version>5.0.5.RELEASE</spring.version>
<hibername.version>5.3.0.CR2</hibername.version>

标签： javahibernatejpamany-to-many

解决方案

问题来自您的 JPQL 查询：

SELECT P FROM Project P INNER JOIN Employee E ON E.external=:external

您应该将其更改为：

SELECT P 
FROM Project P 
INNER JOIN P.employees E 
Where E.external=:external

推荐阅读