Mybatis与Jpa的选择
Jpa的使用非常简洁，开发效率非常高，国际范围内有更多人支持。
但是在中国，有很多人使用Mybatis。
SpringBoot整合Mybatis
安装依赖
<dependency>
<groupId>org.mybatis.spring.boot</groupId>
<artifactId>mybatis-spring-boot-starter</artifactId>
<version>2.1.3</version>
</dependency>
dependencies {
compile("org.mybatis.spring.boot:mybatis-spring-boot-starter:2.1.3")
}
项目配置
# 配置数据库与数据库连接驱动
spring:
datasource:
url: jdbc:mysql://localhost:3306/MoocMall?useUnicode=true&characterEncoding=utf-8&useSSL=false
username: root
password: pass
driver-class-name: com.mysql.jdbc.Driver
通过注解的方式使用Mybatis
public class Category {
private Integer id;
private Integer parentId;
private String name;
private Boolean status;
private Integer sortOrder;
private Date createTime;
private Date updateTime;
}
@Mapper
public interface CategoryMapper {
@Select("select * from category where id = #{id}")
Category selectByPrimaryKey(Integer id);
}
通过配置，测试categoryMapper.selectByPrimaryKey("xxxx")的返回值中部分字段（parentId、sortOrder、createTime、updateTime）值为null，这是因为POJO与数据库的映射没有匹配。可以通过配置mybatis的map-underscore-to-camel-case为ture解决。
spring:
...
mybatis:
configuration:
map-underscore-to-camel-case: true
# 控制台日志配置
log-impl: org.apache.ibatis.logging.stdout.StdOutImpl
Mybatis的mapper组件需要添加@Mapper注解才能被Spring识别，为了方便可以统一在Application的main函数添加mapper包的自动扫描：
@SpringBootApplication
@MapperScan(basePackages = "com.imooc.mall.entities.dao")
public class MallApplication {
public static void main(String[] args) {
SpringApplication.run(MallApplication.class, args);
}
}
IDEA的配置
自动刷新Maven & Gradle依赖
- Build,Excution,Deployment->Build Toold->Maven->Importing
- Build,Excution,Deployment->Build Toold->Gradle
自动倒包
- 手动导入：Option + Enter
- 配置自动：Editor->General->Auto Import
通过XML配置使用Mybatis
public interface CategoryMapper {
Category selectByPrimaryKey(Integer id);
}
指定XML文件扫描路径
# application.yml
spring:
...
mybatis:
configuration:
map-underscore-to-camel-case: true
log-impl: org.apache.ibatis.logging.stdout.StdOutImpl
# 配置XML文件的扫描路径
mapper-locations: classpath:mappers/*.xml
手写Mybatis XML：
查看文档，XML格式
<!--声明-->
<?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.xx.xxx.entities.dao.CategoryMapper">
<select id="selectByPrimaryKey" parameterType="java.lang.Integer" resultType="com.xx.xxx.entities.Category">
select * from category
where id = #{id,jdbcType=INTEGER}
</select>
</mapper>
不建议使用select * ...:
<!--声明-->
<?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.xx.xxx.entities.dao.CategoryMapper">
<sql id="Base_Column_List">
id, parent_id, name, status, sort_order, create_time, update_time
</sql>
<select id="selectByPrimaryKey" parameterType="java.lang.Integer" resultType="com.xx.xxx.entities.Category">
select
<include refid="Base_Column_List" />
from mall_category
where id = #{id,jdbcType=INTEGER}
</select>
</mapper>
mybatis-generator
生成器的原理：连接数据库 -> 获取表结构 -> 生成文件
安装依赖
<plugin>
<groupId>org.mybatis.generator</groupId>
<artifactId>mybatis-generator-maven-plugin</artifactId>
<version>1.4.0</version>
</plugin>
执行命令：mvn mybatis-generator:generate
添加配置文件：src/main/resources/generatorConfig.xml
配置文件内容模板，见文档
配置详解：见博客
例子：
<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE generatorConfiguration
PUBLIC "-//mybatis.org//DTD MyBatis Generator Configuration 1.0//EN"
"http://mybatis.org/dtd/mybatis-generator-config_1_0.dtd">
<generatorConfiguration>
<!--配置connector的绝对路径-->
<classPathEntry location="/Users/lrliang/Desktop/mysql-connector-java-5.1.6.jar" />
<context id="DB2Tables" targetRuntime="MyBatis3">
<!--多次生成XML文件时，覆盖文件，而不是追加xml内容-->
<plugin type="org.mybatis.generator.plugins.UnmergeableXmlMappersPlugin" />
<!--去掉生成文件中的注释-->
<commentGenerator>
<property name="suppressAllComments" value="true"/>
</commentGenerator>
<!--数据库连接配置-->
<jdbcConnection driverClass="com.mysql.jdbc.Driver"
connectionURL="jdbc:mysql://127.0.0.1:3306/Mall?characterEncoding=utf-8"
userId="root"
password="pass">
</jdbcConnection>
<!--设置为false，区分Integer，Long，BigDecimals-->
<javaTypeResolver >
<property name="forceBigDecimals" value="false" />
</javaTypeResolver>
<!--配置生成的Entity文件的路径-->
<javaModelGenerator targetPackage="com.xx.xxx.entities" targetProject="src/main/java">
<property name="enableSubPackages" value="true" />
<property name="trimStrings" value="true" />
</javaModelGenerator>
<!--生成Mybatis XML文件存放的路径-->
<sqlMapGenerator targetPackage="mappers" targetProject="src/main/resources">
<property name="enableSubPackages" value="true" />
</sqlMapGenerator>
<!--生成src下的MapperBean文件路径-->
<javaClientGenerator type="XMLMAPPER" targetPackage="com.xx.xxx.entities.dao" targetProject="src/main/java">
<property name="enableSubPackages" value="true" />
</javaClientGenerator>
<!--数据库表配置-->
<table tableName="order" domainObjectName="Order" enableCountByExample="false" enableDeleteByExample="false" enableSelectByExample="false" enableUpdateByExample="false"/>
</context>
</generatorConfiguration>
配置重复生成的文件覆盖原先生成的文件
<plugin>
<groupId>org.mybatis.generator</groupId>
<artifactId>mybatis-generator-maven-plugin</artifactId>
<version>1.3.7</version>
<configuration>
<overwrite>true</overwrite>
</configuration>
</plugin>
生成的文件
Category
public class Category {
private Integer id;
private Integer parentId;
private String name;
private Boolean status;
private Integer sortOrder;
private Date createTime;
private Date updateTime;
//getter & setter(可以手动删除，使用Lombok @Data注解)
...
}
CategoryMapper
public interface CategoryMapper {
int deleteByPrimaryKey(Integer id);
int insert(Category record);
int insertSelective(Category record);
Category selectByPrimaryKey(Integer id);
int updateByPrimaryKeySelective(Category record);
int updateByPrimaryKey(Category record);
List<Category> selectAll();
}
Mybatis Plugin： 在IDE中将Mapper文件与XML文件关联起来
Mybatis Plugin已经开始收费，可以使用替代版：Free-Mybatis-plugin
Mybatis PageHelper：Mybatis通用分页插件
国人开发、开源的Mybatis通用分页插件：文档及源代码
安装依赖：
<!--mybatis-->
<dependency>
<groupId>org.mybatis.spring.boot</groupId>
<artifactId>mybatis-spring-boot-starter</artifactId>
<version>1.3.1</version>
</dependency>
<!--mapper-->
<dependency>
<groupId>tk.mybatis</groupId>
<artifactId>mapper-spring-boot-starter</artifactId>
<version>1.2.4</version>
</dependency>
<!--pagehelper-->
<dependency>
<groupId>com.github.pagehelper</groupId>
<artifactId>pagehelper-spring-boot-starter</artifactId>
<version>1.2.3</version>
</dependency>
使用案例：
@Override
public ResponseVo<PageInfo> list(Integer categoryId, Integer pageNum, Integer pageSize) {
Set<Integer> categoryIds = new HashSet<>();
if (categoryId != null) {
categoryIds = categoryService.findSubCategoryIds(categoryId);
categoryIds.add(categoryId);
}
// 只需要在需要分页的地方加上PageHelper.startPage
PageHelper.startPage(pageNum, pageSize);
final List<Product> productList = productMapper.selectByCategoryIdSet(categoryIds);
List<ProductVo> productVoList = productList
.stream()
.map(this::product2ProductVo)
.collect(Collectors.toList());
PageInfo pageInfo = new PageInfo<>(productVoList);
pageInfo.setList(productVoList);
return ResponseVo.success(pageInfo);
}
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