MyBatis 注解开发多表查询

• 只需要一个 Mybatis 核心配置文件，不再需要每个Dao接口对应一个XML文件配置sql语句

• 在核心配置文件中将标签中价值映射文件改为加载 ```java <?xml version=”1.0” encoding=”UTF-8” ?> <!DOCTYPE configuration PUBLIC “-//mybatis.org//DTD Config 3.0//EN” “http://mybatis.org/dtd/mybatis-3-config.dtd">

<plugins>
    <plugin interceptor="com.github.pagehelper.PageHelper">
        <property name="dialect" value="mysql"/>
    </plugin>
</plugins>
<!--数据源环境-->
<environments default="development">
    <environment id="development">
        <transactionManager type="JDBC"></transactionManager>
        <dataSource type="POOLED">
            <property name="driver" value="${jdbc.driver}"/>
            <property name="url" value="${jdbc.url}"/>
            <property name="username" value="${jdbc.username}"/>
            <property name="password" value="${jdbc.password}"/>
        </dataSource>
    </environment>
</environments>
<!--采用xml配置开发时-->
<!--加载映射文件-->

<!--采用注解开发-->
<!--加载映射关系-->
<mappers>
    <!--<package name="com\jquan\mapper"/>-->
    <package name="com.jquan.mapper"/>
</mappers>

- 在Dao接口中的方法上面使用注解替代配置XML的方式来实现SQL语句
   - 一对一查询
   - 一对多查询
   - 多对多查询
```java
一对一
select * from orders;
select * from user where id=查询出订单的uid;
一对多
select * from user;
select * from orders where uid=查询出用户的id;
多对多
select * from user;
select * from role r,user_role ur where r.id=ur.role_id and ur.user_id=用户的id


--------------------------java--------------------

package com.jquan.mapper;

import com.jquan.domain.Order;
import com.jquan.domain.User;
import com.sun.org.apache.xpath.internal.operations.Or;
import org.apache.ibatis.annotations.One;
import org.apache.ibatis.annotations.Result;
import org.apache.ibatis.annotations.Results;
import org.apache.ibatis.annotations.Select;

import java.util.List;

public interface OrderMapper {
/*相当于xml开发方式中的 association 标签*/
    @Select(" select *,o.id oid from orders o,user u where o.uid=u.id")
    @Results({
            @Result(column = "oid", property = "id"),
            @Result(column = "ordertime",property = "ordertime"),
            @Result(column = "total",property = "total"),

            @Result(
                    property = "user",
                    column = "uid",
                    javaType = User.class,
                    /*select ‘属性’ 代表查询那个接口的方法获得数据*/
                    one = @One(select ="com.jquan.mapper.UserMapper.findById")
            )

    })
    List<Order> findAll();

   /* @Select(" select *,o.id oid from orders o,user u where o.uid=u.id")
    @Results({
            @Result(column = "oid", property = "id"),
            @Result(column = "ordertime",property = "ordertime"),
            @Result(column = "total",property = "total"),
            @Result(column = "uid",property = "user.id"),//有配置别名
            @Result(column = "username",property = "user.username"),
            @Result(column = "password",property = "user.username"),
            @Result(column = "birthday",property = "user.birthday")
    })
    List<Order> findAll();*/

    @Select("select * from orders where uid=#{uid}")
    List<Order> findByUid(int uid);
}


package com.jquan.mapper;

import com.jquan.domain.Role;
import org.apache.ibatis.annotations.Select;

import java.util.List;

public interface RoleMapper {
    @Select("select * from sys_role r,user u,sys_user_role ur where ur.userid = #{uid} and ur.roleid = r.id")
    List<Role> findByUid(int uid);
}


package com.jquan.mapper;

import com.jquan.domain.User;
import org.apache.ibatis.annotations.Many;
import org.apache.ibatis.annotations.Result;
import org.apache.ibatis.annotations.Results;
import org.apache.ibatis.annotations.Select;

import java.util.List;

public interface UserMapper {

    @Select("select * from user")
    @Results({
            @Result(column = "id",property = "id"),
            @Result(column = "username",property = "username"),
            @Result(column = "password",property = "password"),
            @Result(column = "birthday",property = "birthday"),
            @Result(column = "id",//给 findByUid的参数，ur.userid = #{uid}
                    property = "roleList",javaType = List.class, //封装的字段名
                    many = @Many(select = "com.jquan.mapper.RoleMapper.findByUid")
            )
    })
    List<User> findUserAndRoleAll();

    @Select(" select * from user")
    @Results({
            @Result(column = "id",property = "id"),
            @Result(column = "username",property = "username"),
            @Result(column = "password",property = "password"),
            @Result(column = "birthday",property = "birthday"),
            @Result(column = "id",
                    property = "orderList",javaType = List.class,
                    many = @Many(select = "com.jquan.mapper.OrderMapper.findByUid")
            )
    })
    List<User> findUserAndOrderAll();

    List<User> findAll();

    @Select("select * from user where id=#{id}")
    List<User> findById(int id);

    List<User> findByCondition(User user);
    List<User> findByIds(List<Integer> list);
    void saveUser(User user);
//    void save(User user);



}