java实体外键_如何在JPA中添加用户实体和好友关系实体的外键

现有用户实体，相关代码如下：

@Entity

@Table(name = "t_users")

public class User extends Model {

@Id

@Column(name = "users_id")

@GeneratedValue(strategy = GenerationType.AUTO)

public Long userId;

...

}

以及好友关系实体，相关代码如下：

@Entity

@Table(name = "t_relationship")

public class Relationship extends Model {

@Id

@Column(name = "rs_id")

public Long relationshipId;

@Column(name = "rs_fromuser", nullable = false)

public User fromUser;

@Column(name = "rs_touser", nullable = false)

public User toUser;

...

}

从SQL书写来考虑，只需要在关系实体的两个Column上添加外键约束即可。但却不知道在JPA中应该怎么完成。

我个人数据库相关的知识比较欠缺，在这两个实体是不是多对多关系上存在疑问。

一个用户可以对应多个好友关系，一个好友关系对应固定的两个用户。应该说是n..2这种关系吗？

已经尝试使用@ManyToMany注解，但是我使用的Play 2框架和Ebean没有生成相对应的SQL语句。

@Entity

@Table(name = "t_users")

public class User extends Model {

@Id

@Column(name = "users_id")

@GeneratedValue(strategy = GenerationType.AUTO)

@ManyToMany(cascade = CascadeType.PERSIST, fetch = FetchType.LAZY)

@JoinTable(name = "users_relationship", joinColumns = {

@JoinColumn(name = ("user_id"), referencedColumnName = "userId"),

@JoinColumn(name = ("rs_id"), referencedColumnName = "relationshipId")

})

public Long userId;

...

}

@Entity

@Table(name = "t_relationship")

public class Relationship extends Model {

@Id

@Column(name = "rs_id")

public Long relationshipId;

@Column(name = "rs_fromuser", nullable = false)

@ManyToMany(targetEntity = User.class, mappedBy = "userId")

public User fromUser;

@Column(name = "rs_touser", nullable = false)

@ManyToMany(targetEntity = User.class, mappedBy = "userId")

public User toUser;

...

}

生成的SQL：

create table t_relationship (

rs_id bigint auto_increment not null,

#这里缺少了两个user id列

rs_makedate datetime not null,

rs_accepted tinyint(1) default 0 not null,

constraint pk_t_relationship primary key (rs_id))

;

补充：

后来注意到我需要映射的是User类而非User类的集合，在这里我大概是产生了一定的误解，需要搭配Play相关的内容来检查一下。