HQL Hibernate 内部连接 [英] HQL Hibernate INNER JOIN

问题描述

如何在 Hibernate 中编写此 SQL 查询?我想使用 Hibernate 创建查询，而不是创建数据库.

How can I write this SQL query in Hibernate? I would like to use Hibernate to create queries, not create the database.

SELECT * FROM Employee e INNER JOIN Team t ON e.Id_team=t.Id_team

我在 SQLServer2008 中创建了实体类，

I created entity classes in SQLServer2008,

@Entity
@Table(name="EMPLOYEE")
public class Employee
{
    @Id @GeneratedValue
    @Column(name="ID_EMPLOYEE")
    private int id_employee;
    @Column(name="SURNAME")
    private String surname;
    @Column(name="FIRSTNAME")
    private String firstname;
    @Column(name="ID_PROFESSION")
    private int id_profession;
    @Column(name="ID_BOSS")
    private int id_boss;
    @Column(name="HIRED_DATE")
    private Date hired;
    @Column(name="SALARY")
    private double salary;
    @Column(name="SALARY_ADD")
    private double salary_add;
    @Column(name="ID_TEAM")
    private int id_team;
    //setters and getters
}

@Entity
@Table(name="TEAM")
public class Team
{
    @Id @GeneratedValue
    @Column(name="ID_TEAM")
    private int id_team;
    @Column(name="TEAMNAME")
    private String teamname;
    @Column(name="ADDRESS")
    private String address;
    //setters and getters
}

我尝试以多种方式构建有效的选择查询，但仍然无效.

I tried to build working select query in many ways but it still doesn't work.

SessionFactory sessionFactory = new Configuration().configure().buildSessionFactory();
Session session = sessionFactory.openSession();                 
session.beginTransaction();
String select = "FROM Employee e INNER JOIN Team t ON e.Id_team=t.Id_team";
Query query = session.createQuery(select);
List elist = query.list();
session.getTransaction().commit();
session.close();    

也许实体有问题?

推荐答案

Joins 只能在实体之间存在关联时使用.您的 Employee 实体不应具有映射到列的名为 id_team、类型为 int 的字段.它应该与 Team 实体有一个 ManyToOne 关联，映射为一个 JoinColumn:

Joins can only be used when there is an association between entities. Your Employee entity should not have a field named id_team, of type int, mapped to a column. It should have a ManyToOne association with the Team entity, mapped as a JoinColumn:

@ManyToOne
@JoinColumn(name="ID_TEAM")
private Team team;

然后，以下查询将完美运行:

Then, the following query will work flawlessly:

select e from Employee e inner join e.team

这将加载所有员工，除了那些与任何团队都没有关联的员工.

Which will load all the employees, except those that aren't associated to any team.

同样适用于所有其他字段，这些字段是映射为实体的其他表的外键，当然(id_boss、id_profession).

The same goes for all the other fields which are a foreign key to some other table mapped as an entity, of course (id_boss, id_profession).

是时候阅读 Hibernate 文档了，因为您错过了它是什么以及它是如何工作的一个极其重要的部分.

It's time for you to read the Hibernate documentation, because you missed an extremely important part of what it is and how it works.

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