学步园

多对一(many to one)单向关联映射
多对一的数据库设计原则:在多的那端加外键
//注意在创建实体类属性时应尽量避免与SQL语句中的关键字重名.
用户和组 这里从用户看 多个用户只能对应一个组
只需在多的一端加@ManyToOne

@Entity
@Table(name = "t_user")
public class User {
 private int id;
 private String name;
 private Group group;
 @ManyToOne
 @JoinColumn(name="groupId")//设置外键的名称
 public Group getGroup() {
  return group;
 }
 public void setGroup(Group group) {
  this.group = group;
 }
 @Id
 @GeneratedValue(strategy = GenerationType.AUTO)
 public int getId() {
  return id;
 }
 public void setId(int id) {
  this.id = id;
 }
 public String getName() {
  return name;
 }
 public void setName(String name) {
  this.name = name;
 }
}

@Entity
@Table(name = "t_group")
public class Group {
 private int id;
 private String name;
 @Id
 @GeneratedValue(strategy = GenerationType.AUTO)
 public int getId() {
  return id;
 }
 public void setId(int id) {
  this.id = id;
 }
 public String getName() {
  return name;
 }
 public void setName(String name) {
  this.name = name;
 }
}