HQL Hibernate INNER JOIN [英] HQL Hibernate INNER JOIN

问题描述

我如何在Hibernate中执行这个SQL语句？我想用Hibernate来创建查询，而不是创建数据库。

How can I do this SQL sentence in Hibernate? I would like to use Hibernate to create queries, not create database.

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

我在SQLServer2008中创建实体类，

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;
//set and get

@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;
//set and get

我试图用很多方式构建工作选择查询，但它仍然不起作用。

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();    

可能某物对实体是错误的吗？

Maybe sth is wrong with entities?

推荐答案

连接只能在实体之间存在关联时使用。您的Employee实体不应该有一个名为 id_team ，类型 int 的字段映射到列。它应该与Team实体有一个ManyToOne关联，映射为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，以下查询可以完美地工作：

Then, the following query will work flawlessly:

select e from Employee e inner join e.team

这将加载所有员工，除了那些不与任何团队关联的员工。

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

所有其他字段都是相同的，这些字段是其他字段的外键table当然是映射成一个实体（ 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).

现在是您阅读Hibernate文档的时候了，因为您错过了它的一个非常重要的部分以及它是如何工作的。

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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