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_hero
spring.datasource.username=root
spring.datasource.password=hero
spring.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;
@Mapper
public 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;

@RestController
public class HeroController {

Logger logger= LoggerFactory.getLogger(HeroController.class);

@Autowired
HeroMapper 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 = 0
2017-12-08 14:08:01.318  INFO 8684 --- [nio-8080-exec-6] c.b.mybatis.controller.HeroController    : Insert Hero, Hero Name = hero1, Age = 1
2017-12-08 14:08:01.327  INFO 8684 --- [nio-8080-exec-6] c.b.mybatis.controller.HeroController    : Insert Hero, Hero Name = hero2, Age = 2
2017-12-08 14:08:01.333  INFO 8684 --- [nio-8080-exec-6] c.b.mybatis.controller.HeroController    : Insert Hero, Hero Name = hero3, Age = 3
2017-12-08 14:08:01.340  INFO 8684 --- [nio-8080-exec-6] c.b.mybatis.controller.HeroController    : Insert Hero, Hero Name = hero4, Age = 4
2017-12-08 14:08:01.345  INFO 8684 --- [nio-8080-exec-6] c.b.mybatis.controller.HeroController    : Insert Hero, Hero Name = hero5, Age = 5
2017-12-08 14:08:01.352  INFO 8684 --- [nio-8080-exec-6] c.b.mybatis.controller.HeroController    : Insert Hero, Hero Name = hero6, Age = 6
2017-12-08 14:08:01.357  INFO 8684 --- [nio-8080-exec-6] c.b.mybatis.controller.HeroController    : Insert Hero, Hero Name = hero7, Age = 7
2017-12-08 14:08:01.365  INFO 8684 --- [nio-8080-exec-6] c.b.mybatis.controller.HeroController    : Insert Hero, Hero Name = hero8, Age = 8
2017-12-08 14:08:01.375  INFO 8684 --- [nio-8080-exec-6] c.b.mybatis.controller.HeroController    : Select All, Hero Name hero0, Age = 0
2017-12-08 14:08:01.375  INFO 8684 --- [nio-8080-exec-6] c.b.mybatis.controller.HeroController    : Select All, Hero Name hero1, Age = 1
2017-12-08 14:08:01.375  INFO 8684 --- [nio-8080-exec-6] c.b.mybatis.controller.HeroController    : Select All, Hero Name hero2, Age = 2
2017-12-08 14:08:01.375  INFO 8684 --- [nio-8080-exec-6] c.b.mybatis.controller.HeroController    : Select All, Hero Name hero3, Age = 3
2017-12-08 14:08:01.375  INFO 8684 --- [nio-8080-exec-6] c.b.mybatis.controller.HeroController    : Select All, Hero Name hero4, Age = 4
2017-12-08 14:08:01.375  INFO 8684 --- [nio-8080-exec-6] c.b.mybatis.controller.HeroController    : Select All, Hero Name hero5, Age = 5
2017-12-08 14:08:01.375  INFO 8684 --- [nio-8080-exec-6] c.b.mybatis.controller.HeroController    : Select All, Hero Name hero6, Age = 6
2017-12-08 14:08:01.375  INFO 8684 --- [nio-8080-exec-6] c.b.mybatis.controller.HeroController    : Select All, Hero Name hero7, Age = 7
2017-12-08 14:08:01.375  INFO 8684 --- [nio-8080-exec-6] c.b.mybatis.controller.HeroController    : Select All, Hero Name hero8, Age = 8
2017-12-08 14:08:01.378  INFO 8684 --- [nio-8080-exec-6] c.b.mybatis.controller.HeroController    : Select Hero by Age = 0, Hero Name hero0, Age = 0
2017-12-08 14:08:01.381  INFO 8684 --- [nio-8080-exec-6] c.b.mybatis.controller.HeroController    : Select Hero by Name = hero1, Hero Name hero1, Age = 1
2017-12-08 14:08:01.384  INFO 8684 --- [nio-8080-exec-6] c.b.mybatis.controller.HeroController    : Update Hero by Id = 0, Hero Name hero10, Age = 10
2017-12-08 14:08:01.409  INFO 8684 --- [nio-8080-exec-6] c.b.mybatis.controller.HeroController    : Delete Hero by Id = 1
2017-12-08 14:08:01.416  INFO 8684 --- [nio-8080-exec-6] c.b.mybatis.controller.HeroController    : Delete Hero by Name = hero2
2017-12-08 14:08:01.422  INFO 8684 --- [nio-8080-exec-6] c.b.mybatis.controller.HeroController    : Delete Hero by Age = 3
2017-12-08 14:08:01.429  INFO 8684 --- [nio-8080-exec-6] c.b.mybatis.controller.HeroController    : Delete Hero by Age = 5 and Name = hero5
2017-12-08 14:08:01.432  INFO 8684 --- [nio-8080-exec-6] c.b.mybatis.controller.HeroController    : Select All, Hero Name hero1, Age = 1
2017-12-08 14:08:01.432  INFO 8684 --- [nio-8080-exec-6] c.b.mybatis.controller.HeroController    : Select All, Hero Name hero4, Age = 4
2017-12-08 14:08:01.432  INFO 8684 --- [nio-8080-exec-6] c.b.mybatis.controller.HeroController    : Select All, Hero Name hero6, Age = 6
2017-12-08 14:08:01.432  INFO 8684 --- [nio-8080-exec-6] c.b.mybatis.controller.HeroController    : Select All, Hero Name hero7, Age = 7
2017-12-08 14:08:01.432  INFO 8684 --- [nio-8080-exec-6] c.b.mybatis.controller.HeroController    : Select All, Hero Name hero8, Age = 8
2017-12-08 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