一、解决mapper.xml存放在resources以外路径中的读取问题
在pom.xml文件最后追加< build >标签，以便可以将xml文件复制到classes中，并在程序运行时正确读取。
<build>
<!-- 如果不添加此节点src/main/java目录下的所有配置文件都会被漏掉。 -->
<resources>
<resource>
<directory>src/main/java</directory>
<includes>
<include>**/*.xml</include>
</includes>
</resource>
<resource>
<directory>src/main/resources</directory>
<includes>
<include>**/*.xml</include>
<include>**/*.properties</include>
<include>**/*.ini</include>
</includes>
</resource>
</resources>
</build>二、模糊查询
用 concat('%',#{keyword},'%') <!-- 拼接'%' -->
<mapper namespace="com.zhp.mapper.UserMapper">
<select id="selectUsersByKeyword" resultType="user">
SELECT * FROM t_users
WHERE name LIKE concat('%',#{keyword},'%') <!-- 拼接'%' -->
</select>
</mapper>三、主键回填
标签：< selectKey id="" parameterType="" order="AFTER|BEFORE">
<!--namespace = 所需实现的接口全限定名-->
<mapper namespace="com.zhp.mapper.ProductMapper">
<insert id="insertProduct">
/*主键回填 在插入语句执行之后 查询刚刚插入的 记录 的 id 赋值给 productId */
<selectKey keyProperty="productId" resultType="int" order="AFTER" >
select last_insert_id()
</selectKey>
insert into t_product (productId,productName,brand) values (null,#{productName},#{brand})
</insert>
</mapper>四、MyBatis自动ORM失效
当表的字段和实体类的属性名不同时，自动ORM就会失效，那么这时候我们就可以通过手动配置ORM来解决了
结果映射（ResultMap - 查询结果的封装规则）：
通过 < resultMap id="" type="" > 映射，匹配列名与属性名。
<?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">
<!--namespace = 所需实现的接口全限定名-->
<mapper namespace="com.zhp.mapper.ManagerMapper">
<resultMap id="managerResultMap" type="manager">
<id property="id" column="mgr_id"></id>
<result property="name" column="mgr_name"></result>
<result property="password" column="mgr_pwd"></result>
</resultMap>
<select id="selectManagerByIdAndPwd2" resultMap="managerResultMap">
select * from t_managers where mgr_id = #{id} and mgr_pwd=#{pwd}
</select>
</mapper>五、MyBatis处理关联关系-多表连接【重点】
| 实体间的关系：关联关系（拥有 has、属于 belong）
|
1.一对一
数据准备
DROP TABLE IF EXISTS `t_passenger`;
CREATE TABLE `t_passenger` (
`id` int(11) NOT NULL AUTO_INCREMENT,
`name` varchar(32) DEFAULT NULL,
`sex` varchar(32) DEFAULT NULL,
`birthday` date DEFAULT NULL,
PRIMARY KEY (`id`) USING BTREE
) ENGINE=InnoDB AUTO_INCREMENT=3 DEFAULT CHARSET=utf8mb4 ROW_FORMAT=DYNAMIC COMMENT='乘客';
/*Data for the table `t_passenger` */
insert into `t_passenger`(`id`,`name`,`sex`,`birthday`) values (1,'zs','男','2021-07-29'),(2,'lss','女','2021-07-28');
DROP TABLE IF EXISTS `t_passport`;
CREATE TABLE `t_passport` (
`id` int(11) NOT NULL AUTO_INCREMENT,
`nationality` varchar(32) DEFAULT NULL,
`expire` date DEFAULT NULL,
`passenger_id` int(11) DEFAULT NULL,
PRIMARY KEY (`id`) USING BTREE
) ENGINE=InnoDB AUTO_INCREMENT=3 DEFAULT CHARSET=utf8mb4 ROW_FORMAT=DYNAMIC;
/*Data for the table `t_passport` */
insert into `t_passport`(`id`,`nationality`,`expire`,`passenger_id`) values (1,'中国','2023-07-29',1),(2,'韩国','2023-07-28',2);实体类
public class Passenger {
private Integer id;
private String name;
private String sex;
private Date birthday;
private Passport passport;
}
public class Passport {
private Integer id;
private String nationality;
private Date expire;
private Integer passenger_id;
}.xml中的sql和手动的ORM
<mapper namespace="com.glls.mybatis.mapper.PassengerMapper">
<!-- 结果映射（查询结果的封装规则） -->
<resultMap id="passengerResultMap" type="passenger">
<id property="id" column="id"/>
<result property="name" column="name" />
<result property="sex" column="sex" />
<result property="birthday" column="birthday" />
<!-- 关系表中数据的封装规则 --> <!-- 指定关系表的实体类型 -->
<association property="passport" javaType="passport">
<id property="id" column="passportId"></id>
<result property="nationality" column="nationality"></result>
<result property="expire" column="expire"></result>
<result property="passenger_id" column="passenger_id"></result>
</association>
</resultMap>
<!-- 多表连接查询 --> <!-- 结果映射（查询结果的封装规则）-->
<select id="selectPassengerById" resultMap="passengerResultMap">
<!-- 别名（避免与p1.id冲突） -->
SELECT p1.id , p1.name , p1.sex , p1.birthday , p2.id as passportId , p2.nationality , p2.expire , p2.passenger_id
FROM t_passengers p1 LEFT JOIN t_passports p2
ON p1.id = p2.passenger_id
WHERE p1.id = #{id}
</select>
</mapper>注意：指定“一方”关系时（对象），使用 < association javaType=" ">
