通過ID查詢一個用戶的兩種開發方法

數據庫建表sql語句如下：https://github.com/beyondyanyu/Sayingyy/blob/master/JDBC2-數據庫sql建表語句

①，原始Dao開發：

UserDao.java（接口）:

package com.pdsu.mybatis.dao;import com.pdsu.mybatis.pojo.User;public interface UserDao {//通過用戶ID查詢一個用戶public User selectUserById(Integer id);}

UserDaoImpl.java（實現接口）:

package com.pdsu.mybatis.dao;import org.apache.ibatis.session.SqlSession;
import org.apache.ibatis.session.SqlSessionFactory;import com.pdsu.mybatis.pojo.User;/*** * */
public class UserDaoImpl implements UserDao {//注入SQLSession工廠private SqlSessionFactory sqlsessionFactory;//構造器public UserDaoImpl(SqlSessionFactory sqlsessionFactory) {this.sqlsessionFactory = sqlsessionFactory;}//通過用戶ID查詢一個用戶public User selectUserById(Integer id){SqlSession sqlSession = sqlsessionFactory.openSession(); return sqlSession.selectOne("user.findUserById", id);}
}

MybatisDaoTest.java測試

package com.pdsu.mybatis.junit;import java.io.InputStream;import org.apache.ibatis.io.Resources;
import org.apache.ibatis.session.SqlSessionFactory;
import org.apache.ibatis.session.SqlSessionFactoryBuilder;
import org.junit.Before;
import org.junit.Test;import com.pdsu.mybatis.dao.UserDao;
import com.pdsu.mybatis.dao.UserDaoImpl;
import com.pdsu.mybatis.pojo.User;public class MybatisDaoTest {public SqlSessionFactory sqlSessionFactory;@Beforepublic void before() throws Exception{ //加載核心配置文件，加載要使用IO流進行讀取String resource = "sqlMapConfig.xml";InputStream in = Resources.getResourceAsStream(resource);//創建SqlSessionFactorysqlSessionFactory = new SqlSessionFactoryBuilder().build(in);}@Testpublic void testDao() throws Exception{UserDao userDao = new UserDaoImpl(sqlSessionFactory);User user = userDao.selectUserById(10);System.out.println(user);//輸出結果就是數據庫中ID為10的用戶信息}
}

User.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">
<!-- namespace：命名空間，用于隔離sql，還有一個很重要的作用，后面會講 -->
<!-- 
命名空間：user.findUserById
命名空間：order.findUserById 
--><mapper namespace="com.pdsu.mybatis.mapper.UserMapper"><!-- resultType:返回值parameterType:輸入參數 --><!-- 通過ID查詢一個用戶 --><select id="findUserById" parameterType="Integer" resultType="com.pdsu.mybatis.pojo.User">select * from user where id= #{sq}</select><!-- #{} === select * from user where username=     表示占位符？   sq可以隨意替代=== select * from user where username= '思琪'${} === select * from user where username like '%${value}%'  表示字符串拼接  value不可以隨意替代=== select * from user where username like '%琪%' 			sql 模糊語句查詢=== select * from user where username like "%"'琪%'"%" 		sql 模糊語句查詢=== select * from user where username like "%"#{sq}"%" --><!-- 根據用戶名稱模糊查詢用戶列表 --><select id="findUserByUsername" parameterType="String" resultType="com.pdsu.mybatis.pojo.User">select * from user where username like '%${value}%'</select><!-- 添加用戶 --><insert id="insertUser" parameterType="com.pdsu.mybatis.pojo.User"><selectKey keyProperty="id" resultType="Integer" order="AFTER" >select LAST_INSERT_ID()</selectKey>insert into user(username,birthday,address,sex) values (#{username},#{birthday},#{address},#{sex})</insert><!-- 更新用戶 --><update id="updateUserById" parameterType="com.pdsu.mybatis.pojo.User">update user set username = #{username},sex = #{sex},birthday = #{birthday},address = #{address}where id = #{id}</update>	<!-- 刪除用戶 --><delete id="deleteUserById" parameterType="Integer" >delete from user where id = #{sq}</delete></mapper>

②，Mapper動態代理開發：

UserMapper.java:

package com.pdsu.mybatis.mapper;import java.util.List;import com.pdsu.mybatis.pojo.User;public interface UserMapper {/*遵循四個原則對于：public User findUserById(Integer id);接口   方法名 == User.xml中id名 === findUserById返回值類型 與 Mapper.xml文件中返回值類型（resultType）要一致 === User === com.pdsu.mybatis.pojo.User方法的入參類型 與 Mapper.xml中入參類型（parameterType）要一致 === Integer id命名空間綁定此接口<mapper namespace="com.pdsu.mybatis.mapper.UserMapper">,User.xml中的路徑為該接口全路徑*/public User findUserById(Integer id);}

MybatisMapperTest.java:

package com.pdsu.mybatis.mapper;import static org.junit.Assert.*;import java.io.InputStream;import org.apache.ibatis.io.Resources;
import org.apache.ibatis.session.SqlSession;
import org.apache.ibatis.session.SqlSessionFactory;
import org.apache.ibatis.session.SqlSessionFactoryBuilder;
import org.junit.Test;import com.pdsu.mybatis.pojo.User;public class MybatisMapperTest {@Testpublic void testMapper() throws Exception {//加載核心配置文件，加載要使用IO流進行讀取String resource = "sqlMapConfig.xml";InputStream in = Resources.getResourceAsStream(resource);//創建SqlSessionFactorySqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(in);//SqlSessionFactoryBuilder這是一個實現類需要new一下//創建SQLSessionSqlSession sqlSession = sqlSessionFactory.openSession();	//SqlSession自動生成實現類（接口需要遵循四大原則）=== UserMapper.class為遵循四大原則的接口UserMapper userMapper = sqlSession.getMapper(UserMapper.class);User user = userMapper.findUserById(30);System.out.println(user);//輸出結果就是數據庫中id為30的用戶信息}
}

User.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">
<!-- namespace：命名空間，用于隔離sql，還有一個很重要的作用，后面會講 -->
<!-- 
命名空間：user.findUserById
命名空間：order.findUserById 
--><mapper namespace="com.pdsu.mybatis.mapper.UserMapper"><!-- resultType:返回值parameterType:輸入參數 --><!-- 通過ID查詢一個用戶 --><select id="findUserById" parameterType="Integer" resultType="com.pdsu.mybatis.pojo.User">select * from user where id= #{sq}</select><!-- #{} === select * from user where username=     表示占位符？   sq可以隨意替代=== select * from user where username= '思琪'${} === select * from user where username like '%${value}%'  表示字符串拼接  value不可以隨意替代=== select * from user where username like '%琪%' 			sql 模糊語句查詢=== select * from user where username like "%"'琪%'"%" 		sql 模糊語句查詢=== select * from user where username like "%"#{sq}"%" --><!-- 根據用戶名稱模糊查詢用戶列表 --><select id="findUserByUsername" parameterType="String" resultType="com.pdsu.mybatis.pojo.User">select * from user where username like '%${value}%'</select><!-- 添加用戶 --><insert id="insertUser" parameterType="com.pdsu.mybatis.pojo.User"><selectKey keyProperty="id" resultType="Integer" order="AFTER" >select LAST_INSERT_ID()</selectKey>insert into user(username,birthday,address,sex) values (#{username},#{birthday},#{address},#{sex})</insert><!-- 更新用戶 --><update id="updateUserById" parameterType="com.pdsu.mybatis.pojo.User">update user set username = #{username},sex = #{sex},birthday = #{birthday},address = #{address}where id = #{id}</update>	<!-- 刪除用戶 --><delete id="deleteUserById" parameterType="Integer" >delete from user where id = #{sq}</delete></mapper>

小結（轉載：黑馬程序員）：

selectOne和selectList
動態代理對象調用sqlSession.selectOne()和sqlSession.selectList()是根據mapper接口方法的返回值決定，如果返回list則調用selectList方法，如果返回單個對象則調用selectOne方法。

namespace
mybatis官方推薦使用mapper代理方法開發mapper接口，程序員不用編寫mapper接口實現類，使用mapper代理方法時，輸入參數可以使用pojo包裝對象或map對象，保證dao的通用性。