Spring Boot学习笔记----mybatis注解（一）
之前使用jpa，感觉不错。不用涉及sql便可完成对数据库的增删改查。但项目组要求使用mybatis进行开发，也就用了。两者的区别在于，后者需要进行SQL语句的注解绑定。
网上搜到的mybatis资料，繁琐复杂，多是使用各种配置文件。这对不怎么用XML的开发者来说，简直是头大。因此，还是喜欢注解的方式来解决问题。尽管mybatis官网并不推荐这种方式。官网对于注解的方式，也只是星星点点，躲躲闪闪。
废话不再多说，奔主题。
mybatis如何进行数据库操作呢。需要以下5个步骤。（本文以MAVEN工程为例，开发环境为IDEA，数据库为MySql）
（1）添加Dependence
（2）创建数据库表实例entity。
（3）创建Dao接口，将SQL与方法进行绑定
（4）设置遍历Dao的地址（包名）
（5）使用Dao
我们通过一个实例来看一下整个过程。基于angular的阴影，我们以hero为例。
（1）添加Dependence
<dependency><groupId>org.mybatis.spring.boot</groupId><artifactId>mybatis-spring-boot-starter</artifactId><version>1.3.1</version></dependency>
（2）创建数据库及其表
这是mybatis的硬伤。当然，网上也有博文讲解如何自动生成对应表，类似转基因了，暂且放下，之后再看。
在Application.properties中配置数据库链接，内容如下
spring.datasource.url=jdbc:mysql://127.0.0.1:3306/db_herospring.datasource.username=rootspring.datasource.password=herospring.datasource.driver-class-name=com.mysql.jdbc.Driver
创建语句如下
CREATE SCHEMA `db_hero` ;CREATE TABLE `db_hero`.`hero` ( `id` INT NOT NULL AUTO_INCREMENT, `name` VARCHAR(45) NOT NULL, `age` INT NOT NULL, PRIMARY KEY (`id`));
（3）创建实体类
之前的博文中，有关于IDEA如何自动生成实体类的相关描述，这里不再啰嗦。
（4）创建Dao接口
从代码角度来看，Dao只是一个虚拟接口，但其作用至关重要。它是绑定数据库表，实体类，以及实务操作的枢纽。也是使用注解的关键所在。
先来看最简单的普通查询。使用最简单的增删改查注解。
@Select()@Insert()@Update()@Delete()@Result()
我们来看个简单的例子
package com.breakloop.mybatis.mapper;import com.breakloop.mybatis.entity.Hero;import org.apache.ibatis.annotations.*;import java.util.List;@Mapperpublic interface HeroMapper {@Insert("Insert into hero(name,age) values(#{name},#{age})")@Options(useGeneratedKeys=true, keyColumn="id", keyProperty="id")void addHero(Hero hero);@Update("update hero set name=#{name},age=#{age} where id=#{id}")void updateHero(Hero hero);@Select("select * from hero where name=#{name}")List<Hero> selectHeroByName(String name);@Select("select * from hero where age=#{age}")List<Hero> selectHeroByAge(int age);@Select("select * from hero where id=#{id}")List<Hero> selectHeroById(Long id);@Select("select * from hero")List<Hero> selectAll();@Delete("delete from hero where name=#{name}")void deleteHeroByName(String name);@Delete("delete from hero where age=#{age}")void deleteHeroByAge(int age);@Delete("delete from hero where id=#{id}")void deleteHeroById(Long id);//@Delete("delete from hero where name=#{name} and age=#{age}")//void deleteHero(Hero hero);@Delete("delete from hero where name=#{aa} and age=#{bb}")void deleteHero(@Param("aa") String name,@Param("bb") int age);@Delete("delete from hero")void deleteAll();}
需要注意的是
（a）需要使用#{实体类成员属性}跟列名进行绑定
（b）在添加数据时，对于自增列需要进行注解
@Options(useGeneratedKeys=true, keyColumn="id", keyProperty="id")
（c）如果列名跟实体类成员属性名不同，对于Select，需要对结果进行绑定，使用@Result。
例如，Hero实体类中，sName对应name列，nAge代表age列。
那么，以selectHeroByName为例
@Select("select * from hero where name=#{sName}")@Results( {@Result(id = true, property = "id", column = "id"), @Result(property = "nAge",column = "age"), @Result(property = "sName",column = "name") } ) List<Hero> selectHeroByName(String name);
（d）如果绑定的sql语句相同，将会报错。
这也是代码中屏蔽void deleteHero(Hero hero)方法的原因。该方法与void deleteHero(String sName,int nAge)方法所绑定的sql语句一致。
（e）对于@Param要多说几句。
如果传参不是实体类，或者参数数量大于1，则需要@Param。
如果不用@Param，即使传参名称与实体类属性名（或列名）一致，也会报错（执行方法时）。
错误案例如下
@Delete("delete from hero where name=#{sName} and age=#{nAge}")void deleteHero(String sName,int nAge);
或
@Delete("delete from hero where name=#{name} and age=#{age}")void deleteHero(String name,int age);
注：参考了博文
https://www.cnblogs.com/whisper527/p/6568028.html，但发现$的方式不被识别。不知道是什么原因。有知道的童鞋，还望指点。
（5）标记Dao所在Package
Dao既然如此重要，那么Application该如何找到它呢？有两种方式
（1）在每个Mapper Interface上添加@Mapper
（2）在Application类上添加@MapperScan(“com.breakloop.mybatis.mapper”)，其中com.breakloop.mybatis.mapper为mapper所在包。
若存在多个，则可以使用数组的方式@MapperScan({“com.breakloop.mybatis.mapper”,”com.breakloop.mybatis.entity”})
建议使用第二种方式，不用逐个添加@Mapper
（6）使用Dao
在这里，我们只是简单的在controller中使用Dao，在Logger里打印结果。
package com.breakloop.mybatis.controller;import com.breakloop.mybatis.entity.Hero;import com.breakloop.mybatis.mapper.HeroMapper;import org.slf4j.Logger;import org.slf4j.LoggerFactory;import org.springframework.beans.factory.annotation.Autowired;import org.springframework.web.bind.annotation.RequestMapping;import org.springframework.web.bind.annotation.RestController;import java.util.List;@RestControllerpublic class HeroController {Logger logger= LoggerFactory.getLogger(HeroController.class);@AutowiredHeroMapper mapper;@RequestMapping("/ShowLogger")public void ShowInLogger(){InsertCase();SelectCase();UpdateCase();DeleteCase();}public void InsertCase(){String name;for (int i = 0; i < 9; i++) {Hero hero=new Hero();hero.setAge(i);name="hero"+i;hero.setName(name);mapper.addHero(hero);logger.info("Insert Hero, Hero Name = "+name+", Age = "+i);}}public void SelectCase(){List<Hero> heroes=mapper.selectAll();int age=0;String name="hero1";Long id=2l;for (Hero item :heroes) {logger.info("Select All, Hero Name "+item.getName()+", Age = "+item.getAge());}heroes=mapper.selectHeroByAge(age);if(heroes.size()!=0){for (Hero item :heroes) {logger.info("Select Hero by Age = "+age+", Hero Name "+item.getName()+", Age = "+item.getAge());}}heroes=mapper.selectHeroByName(name);if(heroes.size()!=0){for (Hero item :heroes) {logger.info("Select Hero by Name = "+name+", Hero Name "+item.getName()+", Age = "+item.getAge());}}}public void UpdateCase(){List<Hero> heroes;Long id=0L;int age=10;String name="hero"+age;Hero hero=new Hero();hero.setAge(age);hero.setName(name);hero.setId(id);mapper.updateHero(hero);logger.info("Update Hero by Id = "+id+", Hero Name "+hero.getName()+", Age = "+hero.getAge());heroes=mapper.selectHeroById(id);if(heroes.size()!=0){for (Hero item :heroes) {logger.info("Select Hero by Id = "+id+", Hero Name "+item.getName()+", Age = "+item.getAge());}}}public void DeleteCase(){Long id=1l;String name="hero2";int age=3;List<Hero> heroes;Hero hero;mapper.deleteHeroById(id);logger.info("Delete Hero by Id = "+id);mapper.deleteHeroByName(name);logger.info("Delete Hero by Name = "+name);mapper.deleteHeroByAge(age);logger.info("Delete Hero by Age = "+age);//hero=new Hero();//hero.setName("hero4");//hero.setAge(4);//mapper.deleteHero(hero);//logger.info("Delete Hero by Age = 4 and Name = hero4");mapper.deleteHero("hero5",5);logger.info("Delete Hero by Age = 5 and Name = hero5");heroes=mapper.selectAll();if(heroes.size()!=0){for (Hero item :heroes) {logger.info("Select All, Hero Name "+item.getName()+", Age = "+item.getAge());}}mapper.deleteAll();heroes=mapper.selectAll();if(heroes.size()!=0){for (Hero item :heroes) {logger.info("Select All, Hero Name "+item.getName()+", Age = "+item.getAge());}}else {logger.info("No Hero");}}}
执行结果如下：
2017-12-08 14:08:01.312 INFO 8684 --- [nio-8080-exec-6] c.b.mybatis.controller.HeroController : Insert Hero, Hero Name = hero0, Age = 02017-12-08 14:08:01.318 INFO 8684 --- [nio-8080-exec-6] c.b.mybatis.controller.HeroController : Insert Hero, Hero Name = hero1, Age = 12017-12-08 14:08:01.327 INFO 8684 --- [nio-8080-exec-6] c.b.mybatis.controller.HeroController : Insert Hero, Hero Name = hero2, Age = 22017-12-08 14:08:01.333 INFO 8684 --- [nio-8080-exec-6] c.b.mybatis.controller.HeroController : Insert Hero, Hero Name = hero3, Age = 32017-12-08 14:08:01.340 INFO 8684 --- [nio-8080-exec-6] c.b.mybatis.controller.HeroController : Insert Hero, Hero Name = hero4, Age = 42017-12-08 14:08:01.345 INFO 8684 --- [nio-8080-exec-6] c.b.mybatis.controller.HeroController : Insert Hero, Hero Name = hero5, Age = 52017-12-08 14:08:01.352 INFO 8684 --- [nio-8080-exec-6] c.b.mybatis.controller.HeroController : Insert Hero, Hero Name = hero6, Age = 62017-12-08 14:08:01.357 INFO 8684 --- [nio-8080-exec-6] c.b.mybatis.controller.HeroController : Insert Hero, Hero Name = hero7, Age = 72017-12-08 14:08:01.365 INFO 8684 --- [nio-8080-exec-6] c.b.mybatis.controller.HeroController : Insert Hero, Hero Name = hero8, Age = 82017-12-08 14:08:01.375 INFO 8684 --- [nio-8080-exec-6] c.b.mybatis.controller.HeroController : Select All, Hero Name hero0, Age = 02017-12-08 14:08:01.375 INFO 8684 --- [nio-8080-exec-6] c.b.mybatis.controller.HeroController : Select All, Hero Name hero1, Age = 12017-12-08 14:08:01.375 INFO 8684 --- [nio-8080-exec-6] c.b.mybatis.controller.HeroController : Select All, Hero Name hero2, Age = 22017-12-08 14:08:01.375 INFO 8684 --- [nio-8080-exec-6] c.b.mybatis.controller.HeroController : Select All, Hero Name hero3, Age = 32017-12-08 14:08:01.375 INFO 8684 --- [nio-8080-exec-6] c.b.mybatis.controller.HeroController : Select All, Hero Name hero4, Age = 42017-12-08 14:08:01.375 INFO 8684 --- [nio-8080-exec-6] c.b.mybatis.controller.HeroController : Select All, Hero Name hero5, Age = 52017-12-08 14:08:01.375 INFO 8684 --- [nio-8080-exec-6] c.b.mybatis.controller.HeroController : Select All, Hero Name hero6, Age = 62017-12-08 14:08:01.375 INFO 8684 --- [nio-8080-exec-6] c.b.mybatis.controller.HeroController : Select All, Hero Name hero7, Age = 72017-12-08 14:08:01.375 INFO 8684 --- [nio-8080-exec-6] c.b.mybatis.controller.HeroController : Select All, Hero Name hero8, Age = 82017-12-08 14:08:01.378 INFO 8684 --- [nio-8080-exec-6] c.b.mybatis.controller.HeroController : Select Hero by Age = 0, Hero Name hero0, Age = 02017-12-08 14:08:01.381 INFO 8684 --- [nio-8080-exec-6] c.b.mybatis.controller.HeroController : Select Hero by Name = hero1, Hero Name hero1, Age = 12017-12-08 14:08:01.384 INFO 8684 --- [nio-8080-exec-6] c.b.mybatis.controller.HeroController : Update Hero by Id = 0, Hero Name hero10, Age = 102017-12-08 14:08:01.409 INFO 8684 --- [nio-8080-exec-6] c.b.mybatis.controller.HeroController : Delete Hero by Id = 12017-12-08 14:08:01.416 INFO 8684 --- [nio-8080-exec-6] c.b.mybatis.controller.HeroController : Delete Hero by Name = hero22017-12-08 14:08:01.422 INFO 8684 --- [nio-8080-exec-6] c.b.mybatis.controller.HeroController : Delete Hero by Age = 32017-12-08 14:08:01.429 INFO 8684 --- [nio-8080-exec-6] c.b.mybatis.controller.HeroController : Delete Hero by Age = 5 and Name = hero52017-12-08 14:08:01.432 INFO 8684 --- [nio-8080-exec-6] c.b.mybatis.controller.HeroController : Select All, Hero Name hero1, Age = 12017-12-08 14:08:01.432 INFO 8684 --- [nio-8080-exec-6] c.b.mybatis.controller.HeroController : Select All, Hero Name hero4, Age = 42017-12-08 14:08:01.432 INFO 8684 --- [nio-8080-exec-6] c.b.mybatis.controller.HeroController : Select All, Hero Name hero6, Age = 62017-12-08 14:08:01.432 INFO 8684 --- [nio-8080-exec-6] c.b.mybatis.controller.HeroController : Select All, Hero Name hero7, Age = 72017-12-08 14:08:01.432 INFO 8684 --- [nio-8080-exec-6] c.b.mybatis.controller.HeroController : Select All, Hero Name hero8, Age = 82017-12-08 14:08:01.440 INFO 8684 --- [nio-8080-exec-6] c.b.mybatis.controller.HeroController : No Hero
参考文献
官方文档
http://www.mybatis.org/mybatis-3/zh/java-api.html#sqlSessions
MyBatis使用注解实现增删改查
http://blog.csdn.net/x_iya/article/details/72983906
java 中MyBatis注解映射的实例详解
http://www.jb51.net/article/122942.htm
使用注解配置Mapper
http://blog.csdn.net/kingice1014/article/details/70263148
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