Mybatis复杂映射开发

一. ⼀对⼀查询

（一）⼀对⼀查询的模型

⽤户表和订单表的关系为，⼀个⽤户有多个订单，⼀个订单只从属于⼀个⽤户

⼀对⼀查询的需求：查询⼀个订单，与此同时查询出该订单所属的⽤户

（二）⼀对⼀查询的语句

对应的sql语句：select * from orders o,user u where o.uid=u.id;

查询的结果如下：

 （三）创建Order和User实体

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; 
}

（四）创建OrderMapper接⼝

public interface OrderMapper {
 List<Order> findAll();
}

（五）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>

其中还可以配置如下：

<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>

（六）测试结果

OrderMapper mapper = sqlSession.getMapper(OrderMapper.class);
List<Order> all = mapper.findAll();
for(Order order : all){
 System.out.println(order);
}

二.  ⼀对多查询

（一）⼀对多查询的模型

⽤户表和订单表的关系为，⼀个⽤户有多个订单，⼀个订单只从属于⼀个⽤户

⼀对多查询的需求：查询⼀个⽤户，与此同时查询出该⽤户具有的订单

 

（二）⼀对多查询的语句

对应的sql语句：select *,o.id oid from user u left join orders o on u.id=o.uid;

查询的结果如下：

 （三）修改User实体

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; }

（四）创建UserMapper接⼝

public interface UserMapper {
 List<User> findAll();
}

（五）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="findAll" resultMap="userMap">
 select *,o.id oid from user u left join orders o on u.id=o.uid
 </select>
</mapper>

（六）测试结果

UserMapper mapper = sqlSession.getMapper(UserMapper.class);
List<User> all = mapper.findAll();
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.  多对多查询

（一）多对多查询的模型

⽤户表和⻆⾊表的关系为，⼀个⽤户有多个⻆⾊，⼀个⻆⾊被多个⽤户使⽤

多对多查询的需求：查询⽤户同时查询出该⽤户的所有⻆⾊

（二） 多对多查询的语句

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;

查询的结果如下：

（三） 创建Role实体，修改User实体

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⻆⾊
     private List<Role> roleList; }
     public class Role {
     private int id;
     private String rolename;
}

（四）添加UserMapper接⼝⽅法

List<User> findAllUserAndRole();

（五）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>

（六）测试结果

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("----------------------------------");
}

（七）知识⼩结

 

MyBatis多表配置⽅式：

⼀对⼀配置：使⽤做配置

⼀对多配置：使⽤+做配置

多对多配置：使⽤+做配置