1.Mybatis資料查詢步驟
2.在mappers映射器下建立檔案(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中對goods.xml聲明
<?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>
<!-- 環境,可以配置多個,default:指定采用哪個環境 -->
<environments default="dev">
<!-- id:唯一辨別 -->
<environment id="dev">
<!--采用JDBC進行事務的管理commit/rollback-->
<transactionManager type="JDBC"/>
<!-- 資料源,連接配接池類型的資料源 -->
<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>
<!--聲明mapper的配置檔案-->
<mappers>
<mapper resource="mappers/goods.xml"/>
</mappers>
</configuration>
4.測試語句
/**
* select查詢語句執行
*
* @throws Exception
*/
@Test
public void testSelectAll() throws Exception
{
SqlSession session = null;
try
{
session = MyBatisUtils.openSession();
List<Goods> list = session.selectList("goods.selectAll");//goods.selectAll 命名空間.(SQL語句的ID)
for (Goods g : list)
{
System.out.println(g.getTitle());
}
}
catch (Exception e)
{
throw e;
}
finally
{
MyBatisUtils.closeSession(session);
}
}
5.在mybatis-config.xml中開啟駝峰命名轉換
<settings>
<!-- goods_id ==> goodsId 駝峰命名轉換 -->
<setting name="mapUnderscoreToCamelCase" value="true"/>
</settings>
6.CRUD标簽(select标簽)
select – 書寫查詢sql語句
select中的幾個屬性說明:
id屬性:目前名稱空間下的statement的唯一辨別。必須。要求id和mapper接口中的方法的名字一緻。
resultType:将結果集映射為java的對象類型。必須(和 resultMap 二選一)
parameterType:傳入參數類型。可以省略