mybatis学习第五部分：Mybatis复杂映射开发

5.1 ⼀对⼀查询

5.1.1 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

5.1.2⼀对⼀查询的语句

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

查询的结果如下：

5.1.3 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;
}

5.1.3 创建OrderMapper接⼝

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

5.1.3 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>

5.1.6 测试结果

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

5.2 ⼀对多查询

5.2.1 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

5.2.2 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：

5.2.3 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;
}

5.2.3 创建UserMapper接⼝

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

5.2.3 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>

测试代码：

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

5.2.6 测试结果

5.3 多对多查询

5.3.1 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

5.3.2 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：

5.3.3 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;
}

5.3.4 添加UserMapper接⼝⽅法

List<User> findAllUserAndRole();

5.3.5 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>

5.3.6 测试代码

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

5.3.7 测试结果：