1.Mybatis数据查询步骤
2.在mappers映射器下创建文件(src/main/resources/mappers/goods.xml)
<?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="goods">
<select id="selectAll" resultType="com.imooc.mybatis.entity.Goods" >
select *
from t_goods
order by goods_id desc limit 10
</select>
</mapper>
3.在mybatis-config.xml中对goods.xml声明
<?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">
<configuration>
<!-- 环境,可以配置多个,default:指定采用哪个环境 -->
<environments default="dev">
<!-- id:唯一标识 -->
<environment id="dev">
<!--采用JDBC进行事务的管理commit/rollback-->
<transactionManager type="JDBC"/>
<!-- 数据源,连接池类型的数据源 -->
<dataSource type="POOLED">
<property name="driver" value="com.mysql.cj.jdbc.Driver"/>
<property name="url"
value="jdbc:mysql://localhost:3306/babytun?useUnicode=true&characterEncoding=UTF-8&serverTimezone=UTC"/>
<property name="username" value="root"/>
<property name="password" value="197366"/>
</dataSource>
</environment>
</environments>
<!--声明mapper的配置文件-->
<mappers>
<mapper resource="mappers/goods.xml"/>
</mappers>
</configuration>
4.测试语句
/**
* select查询语句执行
*
* @throws Exception
*/
@Test
public void testSelectAll() throws Exception
{
SqlSession session = null;
try
{
session = MyBatisUtils.openSession();
List<Goods> list = session.selectList("goods.selectAll");//goods.selectAll 命名空间.(SQL语句的ID)
for (Goods g : list)
{
System.out.println(g.getTitle());
}
}
catch (Exception e)
{
throw e;
}
finally
{
MyBatisUtils.closeSession(session);
}
}
5.在mybatis-config.xml中开启驼峰命名转换
<settings>
<!-- goods_id ==> goodsId 驼峰命名转换 -->
<setting name="mapUnderscoreToCamelCase" value="true"/>
</settings>
6.CRUD标签(select标签)
select – 书写查询sql语句
select中的几个属性说明:
id属性:当前名称空间下的statement的唯一标识。必须。要求id和mapper接口中的方法的名字一致。
resultType:将结果集映射为java的对象类型。必须(和 resultMap 二选一)
parameterType:传入参数类型。可以省略