mybatis 一对一，一对多，多对多映射开发
作者：互联网
目录
一、一对一映射查询
例：一个订单对应一个用户。
对应的sql语句：select * from orders o,user u where o.uid=u.id;
1、实体类
public class Order {
private int id;
private Date ordertime;
private double total;
//代表当前订单从属于哪一个客户
private User user;
}
public class User {
private int id;
private String username;
private String password;
private Date birthday;
}
2、mapper接口，OrderMapper
public interface OrderMapper {
List<Order> findAll();
}
3、mapper配置，OrderMapper.xml
<mapper namespace="com.lagou.mapper.OrderMapper">
<resultMap id="orderMap" type="com.lagou.domain.Order">
<result column="uid" property="user.id"></result>
<result column="username" property="user.username"></result>
<result column="password" property="user.password"></result>
<result column="birthday" property="user.birthday"></result>
</resultMap>
<select id="findAll" resultMap="orderMap">
select * from orders o,user u where o.uid=u.id
</select>
</mapper>
又或者这样配置 resultMap：
<resultMap id="orderMap" type="com.lagou.domain.Order">
<result property="id" column="id"></result>
<result property="ordertime" column="ordertime"></result>
<result property="total" column="total"></result>
<association property="user" javaType="com.lagou.domain.User">
<result column="uid" property="id"></result>
<result column="username" property="username"></result>
<result column="password" property="password"></result>
<result column="birthday" property="birthday"></result>
</association>
</resultMap>
4、使用注解配置 mapper
public interface OrderMapper {
@Select("select * from orders")
@Results({
@Result(id=true, property="id", column="id"),
@Result(property="ordertime", column="ordertime"),
@Result(property="total", column="total"),
@Result(property="user", column="uid", javaType=User.class,
one=@One(select="com.lagou.mapper.UserMapper.findById"))
})
List<Order> findAll();
}
public interface UserMapper {
@Select("select * from user where id=#{id}")
User findById(int id);
}
5、结果测试
@Test
public void testSelectOrderAndUser() {
List<Order> all = orderMapper.findAll();
for(Order order : all){
System.out.println(order);
}
}
二、一对多映射查询
对应的sql语句：select *,o.id oid from user u left join orders o on u.id=o.uid;
1、实体类
public class Order {
private int id;
private Date ordertime;
private double total;
//代表当前订单从属于哪一个客户
private User user;
}
public class User {
private int id;
private String username;
private String password;
private Date birthday;
//代表当前用户具备哪些订单
private List<Order> orderList;
}
2、mapper接口，UserMapper
public interface UserMapper {
List<User> findAllUserAndOrder();
}
3、mapper配置，UserMapper.xml
<mapper namespace="com.lagou.mapper.UserMapper">
<resultMap id="userMap" type="com.lagou.domain.User">
<result column="id" property="id"></result>
<result column="username" property="username"></result>
<result column="password" property="password"></result>
<result column="birthday" property="birthday"></result>
<collection property="orderList" ofType="com.lagou.domain.Order">
<result column="oid" property="id"></result>
<result column="ordertime" property="ordertime"></result>
<result column="total" property="total"></result>
</collection>
</resultMap>
<select id="findAllUserAndOrder" resultMap="userMap">
select *,o.id oid from user u left join orders o on u.id=o.uid
</select>
</mapper>
4、使用注解配置 mapper
public interface UserMapper {
@Select("select * from user")
@Results({
@Result(id=true, property="id", column="id"),
@Result(property="username", column="username"),
@Result(property="password", column="password"),
@Result(property="birthday", column="birthday"),
@Result(property="orderList", column="id", javaType=List.class,
many=@Many(select = "com.lagou.mapper.OrderMapper.findByUid"))
})
List<User> findAllUserAndOrder;
}
public interface OrderMapper {
@Select("select * from orders where uid=#{uid}")
List<Order> findByUid(int uid);
}
5、结果测试
List<User> all = userMapper.findAllUserAndOrder();
for(User user : all){
System.out.println(user.getUsername());
List<Order> orderList = user.getOrderList();
for(Order order : orderList){
System.out.println(order);
}
System.out.println("-----------------------------");
}
三、多对多映射开发
对应的sql语句：select u.,r.,r.id rid from user u left join user_role ur on u.id=ur.user_id inner join role r on ur.role_id=r.id;
1、实体类
public class User {
private int id;
private String username;
private String password;
private Date birthday;
//代表当前用户具备哪些订单
private List<Order> orderList;
//代表当前用户具备哪些角色
private List<Role> roleList;
}
public class Role {
private int id;
private String rolename;
}
2、添加mapper接口方法，UserMapper
public interface UserMapper {
List<User> findAllUserAndRole();
}
3、mapper配置，UserMapper.xml
<resultMap id="userRoleMap" type="com.lagou.domain.User">
<result column="id" property="id"></result>
<result column="username" property="username"></result>
<result column="password" property="password"></result>
<result column="birthday" property="birthday"></result>
<collection property="roleList" ofType="com.lagou.domain.Role">
<result column="rid" property="id"></result>
<result column="rolename" property="rolename"></result>
</collection>
</resultMap>
<select id="findAllUserAndRole" resultMap="userRoleMap">
select u.*,r.*,r.id rid from user u
left join user_role ur on u.id=ur.user_id
inner join role r on ur.role_id=r.id
</select>
4、使用注解配置 mapper
public interface UserMapper {
@Select("select * from user")
@Results({
@Result(id=true, property="id", column="id"),
@Result(property="username", column="username"),
@Result(property="password", column="password"),
@Result(property="birthday", column="birthday"),
@Result(property="roleList", column="id", javaType=List.class,
many=@Many(select="com.lagou.mapper.RoleMapper.findByUid"))
})
List<User> findAllUserAndRole();
}
public interface RoleMapper {
@Select("select * from Role r, user_role ur where r.id=ur.role_id and ur.user_id=#{id}")
List<Role> findByUid(int uid);
}
5、结果测试
UserMapper mapper = sqlSession.getMapper(UserMapper.class);
List<User> all = mapper.findAllUserAndRole();
for(User user : all){
System.out.println(user.getUsername());
List<Role> roleList = user.getRoleList();
for(Role role : roleList){
System.out.println(role);
}
System.out.println("----------------------------------");
}
标签：mapper,映射,一对一,List,private,public,user,mybatis,id 来源： https://blog.csdn.net/jason559/article/details/120362032