[英]JPA join in spring boot application
我已经阅读了一些例子,但我有个人问题。 我有2张桌子:
Role: id, name User: id, login, name, role_id
@Entity
@Table(name = "role")
public class Role {
@Id
@Column(name = "id")
private long id;
@Column(name = "name", length = 45)
private String name;
@OneToMany(cascade = CascadeType.ALL, mappedBy = "role")
private Set<User> user = new HashSet<>();
//getters and setters
@Entity
@Table(name = "user")
public class User {
@Id
@GeneratedValue(strategy = GenerationType.AUTO)
@Column(name = "id",insertable = false, updatable = false)
private long id;
@Column(name = "login")
private String login;
@Column(name = "user_name")
private String userName;
@ManyToOne(fetch = FetchType.LAZY)
private Role role;
//getters and setters
public interface UserRepository extends JpaRepository<User, Long> {
String Q_GET_ALL_USERS = "from User u left join Role r on u.role_id=r.id";
@Query(Q_GET_ALL_USERS)
Collection<User> getAllUsers();
此代码显示: Caused by: java.lang.IllegalArgumentException: org.hibernate.hql.internal.ast.QuerySyntaxException: Path expected for join! [from com.example.jpa.model.User u left join Role r on u.role_id=r.id]
以下Caused by: java.lang.IllegalArgumentException: org.hibernate.hql.internal.ast.QuerySyntaxException: Path expected for join! [from com.example.jpa.model.User u left join Role r on u.role_id=r.id]
Caused by: java.lang.IllegalArgumentException: org.hibernate.hql.internal.ast.QuerySyntaxException: Path expected for join! [from com.example.jpa.model.User u left join Role r on u.role_id=r.id]
我如何理解实体不能包含'id'(在我的情况下在Role
)的引用,我应该删除这个字段。 但实体应该有'@Id'。
在这种情况下,我应该在'Role'中创建新列? 或者我可以使用更美丽的决定?
我把所有项目都放到了bb
要在HQL(JPQL)中使用join,您不需要on
子句
String Q_GET_ALL_USERS = "select u from User u left join u.role";
由于您没有在where子句中使用role
,因此此查询没有任何意义。
如果要获取具有获取角色的用户,可以使用join fetch
String Q_GET_ALL_USERS = "select u from User u left join fetch u.role";
更新
您的User
和Role
架构不常用。 我给你的建议做出@ManyToMany
从用户关联的角色和删除任何user
从关联Role
@Entity
@Table(name = "user")
public class User {
@ManyToMany(fetch = FetchType.LAZY)
private Set<Role> roles;
}
@Entity
@Table(name = "role")
public class Role {
@Id
@Column(name = "id")
private long id;
@Column(name = "name", length = 45)
private String name;
}
不,您应该在User
创建一个新列。
@ManyToOne(fetch = FetchType.LAZY)
@JoinColumn(name = "role_id")
private Role role;
谢谢大家的答案。 正确的实体和下面的查询(加上表架构)。
表(查询)
CREATE TABLE role (
id INT NOT NULL PRIMARY KEY,
name VARCHAR(45) NOT NULL
);
CREATE TABLE user (
id INT NOT NULL PRIMARY KEY IDENTITY,
login VARCHAR(45) NOT NULL,
user_name VARCHAR(45) NOT NULL,
role_id INT NOT NULL,
FOREIGN KEY (role_id) REFERENCES role (id)
);
实体:
@Entity
@Table(name = "user")
public class User {
@Id
@GeneratedValue(strategy = GenerationType.AUTO)
@Column(name = "id",insertable = false, updatable = false)
private long id;
@Column(name = "login")
private String login;
@Column(name = "user_name")
private String userName;
@ManyToOne(fetch = FetchType.LAZY)
private Role role;
//getters and setters
}
和
@Entity
@Table(name = "role")
public class Role {
@Id
@Column(name = "id")
private long id;
@Column(name = "name", length = 45)
private String name;
@OneToMany(cascade = CascadeType.ALL, mappedBy = "role")
private Set<User> user = new HashSet<>();
//getters and setters
}
知识库
public interface UserRepository extends JpaRepository<User, Long> {
String Q_GET_ALL_USERS = "select u from User u left join u.role";
@Query(Q_GET_ALL_USERS)
Collection<User> getAllUsers();
}
@ v-ladynev提出了替代决定(在User
仅使用@ManyToMany
)。 您可以在此答案的评论中找到更多详细信息。 当我检查这个决定时,我会更新这个答案(我希望我不要忘记它:-))
楷模
@Entity
@Table(name = "sys_std_user")
public class StdUser {
@Id
@GeneratedValue(strategy = GenerationType.AUTO)
@Column(name = "class_id")
public int classId;
@Column(name = "user_name")
public String userName;
}
@Entity
@Table(name = "sys_std_profile")
public class StdProfile {
@Id
@Column(name = "pro_id")
public int proId;
@Column(name = "full_name")
public String fullName;
}
控制器
@PersistenceUnit
private EntityManagerFactory emf;
@GetMapping("/join")
public List actionJoinTable() {
EntityManager em = emf.createEntityManager();
List arr_cust = em
.createQuery("SELECT u.classId, u.userName, p.fullName FROM StdUser u, StdProfile p WHERE u.classId=p.proId")
.getResultList();
return arr_cust;
}
结果:
[
[
1,
"Ram",
"Ram Pukar Chaudhary"
],
[
2,
"Raja",
"Raja Kishor Shah"
]
]
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