9

我对 SQL 和 JPQL 的理解不是很好,我一直在尝试创建以下 sql 语句的 JPQL 查询:

select group.* from user, user_group, group 
where user_group.user_id = user.id 
and user_group.group_id = group.id 
and user.id = [userID to search]

编辑:糟糕,我忘记将按用户 ID 搜索的部分添加到查询中。我想获取用户所属的所有组。

但我只是无法正确地获取语法。任何帮助将不胜感激。

相关代码片段:

组.java

@Table(name = "group")
@Entity
public class Group implements Serializable {

@Id
@GeneratedValue
@Column(name = "id")
private Integer id;

@JoinTable(name = "user_group", joinColumns = {
    @JoinColumn(name = "group_id", referencedColumnName = "id")}, inverseJoinColumns = {
    @JoinColumn(name = "user_id", referencedColumnName = "id")})
@ManyToMany
private Collection<User> userCollection;

}

用户.java

@Table(name = "user")
@Entity
public class User implements Serializable {

@Id
@NotNull
@GeneratedValue
@Column(name = "id")
private Integer id;

@Column(name = "email", unique=true, nullable=false)
private String email;

@ManyToMany(mappedBy = "userCollection")
private Collection<Group> GroupCollection;
}
4

1 回答 1

12

使用 JPQL 将是:

TypedQuery<Group> query = em.createQuery(
    "SELECT DISTINCT g FROM User u LEFT JOIN u.groupCollection g " +
    "WHERE u = :user", Group.class);
query.setParameter("user", user);
List<Group> = query.getResultsList();

em您的 EntityManager在哪里,并且user是要为其加载组列表的 User 类的实例。如果您只有用户 ID,请更改为:

TypedQuery<Group> query = em.createQuery(
    "SELECT DISTINCT g FROM User u LEFT JOIN u.groupCollection g " +
    "WHERE u.id = :user", Group.class);
query.setParameter("user", userId);

最好使用 a Setor SortedSet(或者List如果用户可以多次在同一个组中,则可以使用 a )而不是 a Collection

于 2012-11-21T03:27:14.670 回答