1.一对一的关系关联

需求：用户和角色一对一关联

packageimport javax.persistence.*;

@Entity
@Table(name = "t_user")
public class)
    private)
    private/***///JoinColumn:维护一个外键的作用
    privatepublicreturnpublic voidthis.id =publicreturnpublic voidthis.name =publicreturnpublic voidthis.role = role;
    }
}
packageimport javax.persistence.*;

@Entity
@Table(name = "t_role")
public class)
    private)
    private)
    privatepublicreturnpublic voidthis.id =publicreturnpublic voidthis.name =publicreturnpublic voidthis.user = user;
    }
}
/***/public void//创建角色
        Role role =new);

        //创建用户
        User user =new);

        //建立关系
//保存数据
/***/public voidlong)13);
        System.out.println(user);
        Role role = user.getRole();
        System.out.println(role);

    }

2.一对多关联关系

需求：从角色到用户的一对多关联关系

packageimport javax.persistence.*;

@Entity
@Table(name = "t_user")
public class)
    private)
    private)
    privatepublicreturnpublic voidthis.id =publicreturnpublic voidthis.name =publicreturnpublic voidthis.role = role;
    }
}
packageimport javax.persistence.*;
importimport)
public class)
    private)
    private)
    private Set<User> userSet = new HashSet<>();

    publicreturnpublic voidthis.id =publicreturnpublic voidthis.name =public Set<User>returnpublic void setUserSet(Set<User>this.userSet = userSet;
    }
}
/***/public void//创建角色
        Role role =new);

        //创建用户
        User user =new);

        //建立关系
//保存数据
/***/public voidlong)13);
        System.out.println(user);
        Role role = user.getRole();
        System.out.println(role);

    }

3.多对多的关联关系

需求：用户和角色多对多关系

packageimport javax.persistence.*;
importimport)
public class)
    private)
    private//fetch = FetchType.EAGER:异步加载
    //JoinTable 配置中间表信息
    //joinColumns 建立当前表在中间表中的外键字段
    @JoinTable(name = "t_user_role",joinColumns = @JoinColumn(name = "user_id")
            ,inverseJoinColumns = @JoinColumn(name = "role_id"))
   private Set<Role> roles =new HashSet<>();

    publicreturnpublic voidthis.id =publicreturnpublic voidthis.name =public Set<Role>returnpublic void setRoles(Set<Role>this.roles = roles;
    }
}
packageimport javax.persistence.*;
importimport)
public class)
    private)
    private)
    private Set<User> users =new HashSet<>();

    publicreturnpublic voidthis.id =publicreturnpublic voidthis.name =public Set<User>returnpublic void setUsers(Set<User>this.users = users;
    }
}
/***/public void//创建角色
        Role role =new);

        //创建用户
        User user1 =new);

        User user2 =new);


        //建立关系
//保存数据
/***/public voidlong)13);
        System.out.println(user);
        Set<Role> roles = user.getRoles();
        System.out.println(roles);

    }