[英]sql query with join using hibernate
in my project I created this class: 在我的项目中,我创建了此类:
@Entity
@Table(name= "Wall")
public class Wall {
@Id
@GeneratedValue
@Column(name="id")
private Integer id;
@ManyToOne
@JoinColumn(name="user_id", nullable=false)
private User user;
@ManyToOne
@JoinColumn(name="likable_id", nullable=false)
private Likable likable;
@ManyToMany(cascade = { CascadeType.ALL })
@JoinTable(
name= "Wall_Follower",
joinColumns = { @JoinColumn(name = "wall_id") },
inverseJoinColumns = { @JoinColumn(name = "follower_id") }
)
private Set<User> followers;
who gives this tables: 谁提供此表:
Wall
+----+------------+---------+
| id | likable_id | user_id |
+----+------------+---------+
Wall_Follower
+---------+-------------+
| wall_id | follower_id |
+---------+-------------+
And I would like to search the followers. 我想搜索关注者。 With an SQL query it would give:
使用SQL查询,它将给出:
SELECT * FROM `Wall_Follower` AS MF
LEFT JOIN `Wall` AS M
ON MF.wall_id= M.wall_id
WHERE MF.follower_id = 1
I thought of doing a class Follower like this: 我想到做一个这样的班级追随者:
@Entity
@Table(name= "Mur_Follower")
public class Follower {
@Id
@Column(name="follower_id")
private Integer id;
@Column(name="mur_id")
private Mur mur;
but I have an error: 但我有一个错误:
Could not determine type for: beans.Wall, at table: Wall_Follower, for columns: [org.hibernate.mapping.Column(wall_id)]
You need to have bidirectional mapping as Wall_follower is having many to many relationship. 您需要双向映射,因为Wall_follower具有多对多关系。
@Entity
@Table(name= "Mur_Follower")
public class Follower {
@Id
@Column(name="follower_id")
private Integer id;
@Column(name="mur_id")
private Mur mur;
@ManyToMany(cascade = { CascadeType.ALL })
@JoinTable(
name= "Wall_Follower",
joinColumns = { @JoinColumn(name = "follower_id") },
inverseJoinColumns = { @JoinColumn(name = "wall_id") }
)
private Set<Wall> walls;
Also, change your mapping in wall class as follows 另外,按以下方式在wall类中更改映射
@ManyToMany(cascade = { CascadeType.ALL })
@JoinTable(
name= "Wall_Follower",
joinColumns = { @JoinColumn(name = "wall_id") },
inverseJoinColumns = { @JoinColumn(name = "follower_id") }
)
private Set<Follower> followers;
声明:本站的技术帖子网页,遵循CC BY-SA 4.0协议,如果您需要转载,请注明本站网址或者原文地址。任何问题请咨询:yoyou2525@163.com.