Mybatis多表查询
### 1.Mybatis多表查询
#### 1.1 一对一查询
##### 1.1.1 一对一查询的模型MapperScannerConfigurer
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
##### 1.1.2一对一查询的语句
对应的sql语句：select * from orders o,user u where o.uid=u.id;
查询的结果如下：
##### 1.1.3 创建Order和User实体
```java
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;
}
1.1.4 创建OrderMapper接口
public interface OrderMapper {
List<Order> findAll();
}
1.1.5 配置OrderMapper.xml
<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN" "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
<mapper namespace="com.code_g.dao.OrderMapper">
<resultMap id="orderMap" type="Order">
<id column="oid" property="id"/>
<result column="ordertime" property="ordertime"/>
<result column="total" property="total"/>
<!-- <result column="uid" property="user.id"/>-->
<!-- <result column="username" property="user.username"/>-->
<!-- <result column="password" property="user.password"/>-->
<!-- property实体属性名称 javaType实体属性类型-->
<association property="user" javaType="User">
<id column="uid" property="id"/>
<result column="username" property="username"/>
<result column="password" property="password"/>
</association>
</resultMap>
<select id="findAll" resultMap="orderMap">
select *,o.id oid from orders o,user u where o.uid = u.id
</select>
</mapper>
1.1.6 测试结果
OrderMapper mapper = sqlSession.getMapper(OrderMapper.class);
List<Order> all = mapper.findAll();
for(Order order : all){
System.out.println(order);
}
1.2 一对多查询
1.2.1 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
1.2.2 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：
1.2.3 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;
}
1.2.4 创建UserMapper接口
public interface UserMapper {
List<User> findAllOrders();
}
1.2.5 配置UserMapper.xml
<mapper namespace="com.code_g.mapper.UserMapper">
<resultMap id="userMap" type="User">
<id column="uid" property="id"/>
<result column="username" property="username"/>
<result column="password" property="password"/>
<!-- collection property集合名称 ofType集合中的数据类型-->
<collection property="orderList" ofType="Order">
<id column="oid" property="id"/>
<result column="ordertime" property="ordertime"/>
<result column="total" property="total"/>
</collection>
</resultMap>
<select id="findAllOrders" resultMap="userMap">
SELECT *,o.id oid FROM USER u,orders o WHERE u.`id` = o.`uid`
</select>
</mapper>
1.2.6 测试结果
UserMapper mapper = sqlSession.getMapper(UserMapper.class);
List<User> all = mapper.findAllOrders();
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("----------------------------------");
}
1.3 多对多查询
1.3.1 多对多查询的模型
用户表和角色表的关系为，一个用户有多个角色，一个角色被多个用户使用
多对多查询的需求：查询用户同时查询出该用户的所有角色
1.3.2 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：
1.3.3 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角色
private List<Role> roleList;
}
public class Role {
private int id;
private String rolename;
}
1.3.4 添加UserMapper接口方法
List<User> findAllUserAndRole();
1.3.5 配置UserMapper.xml
<resultMap id="userRoleMap" type="com.code_g.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.code_g.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>
1.3.6 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("----------------------------------");
}
MyBatis多表配置方式：
一对一配置：使用
一对多配置：使用
多对多配置：使用
