Question

正如标题所示，我试图通过使用以下查询来选择用户名和角色名称。

select u.username, r.name
from users u, role r
inner join users_roles ur
  on ur.user_id = u.id
where username = ?;

但是我收到以下错误

[2017-04-05 21:34:49] [42P01] ERROR: invalid reference to FROM-clause entry for table "u"
[2017-04-05 21:34:49] Hint: There is an entry for table "u", but it cannot be referenced from this part of the query.
[2017-04-05 21:34:49] Position: 79

我的用户实体如下

@Entity(name = "users") // Postgres doesn't like the table name "user"
public class User {
    @Id
    @GeneratedValue(strategy = GenerationType.AUTO)
    private long id;
    private String username;
    ...

    @ManyToMany
    @JoinTable(
            name = "users_roles",
            joinColumns = @JoinColumn(
                    name = "user_id", referencedColumnName = "id"),
            inverseJoinColumns = @JoinColumn(
                    name = "role_id", referencedColumnName = "id"))
    private Collection<Role> roles;
...

我的角色实体如下

@Entity
public class Role {
    @Id
    @GeneratedValue(strategy = GenerationType.AUTO)
    private long id;
    private String name;
    @ManyToMany(mappedBy = "roles")
    private Collection<User> users;
...

关于我做错了什么的线索？

Answer 1

SELECT users.username, role.name
FROM users
LEFT OUTER JOIN users_roles
  ON users.id = users_roles.user_id
LEFT OUTER JOIN role
  ON users_roles.role_id = role.id
WHERE username = ?

选择用户名和角色名称

1 个答案: