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MyBatis-resultType参数

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1、resultType概述

resultType 属性可以指定结果集的类型,它支持基本类型和实体类类型。
需要注意的是,它和 parameterType 一样,如果注册过类型别名的,可以直接使用别名。没有注册过的必须使用全限定类名。

同时,当是实体类名称时,还有一个要求,实体类中的属性名称必须和查询语句中的列名保持一致,否则无法实现封装。

例如:我们的实体类此时必须是全限定类名(今天讲解如何配置实体类的别名)

2、需求分析

基本类型:查询数据库表(user)中的所有记录数的统计。

实体类型:查询数据库表(user)中的所有记录

3、案例回顾(基本类型)

3.1、编写IUserDao.java文件

package com.tianyi.dao; public interface IUserDao { int allCount(); }

3.2、编写IUserDao.xml文件

<?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.tianyi.dao.IUserDao"> <select id="allCount" resultType="int"> select count(*) from user </select> </mapper>

3.3、编写MbTest1.java文件

package com.tianyi.test; import com.tianyi.dao.IUserDao; import com.tianyi.javabean.QueryUser; import com.tianyi.javabean.User; 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.After; import org.junit.Before; import org.junit.Test; import java.io.InputStream; import java.util.Date; import java.util.List; public class MbTest1 { private InputStream in ; private SqlSessionFactory factory; private SqlSession session; private IUserDao userDao; @Test public void allCount(){ int n=userDao.allCount(); System.out.println(n); } @Test public void findByUser(){ QueryUser qu=new QueryUser(); User u=new User(); u.setUsername("%王%"); qu.setUser(u); List<User> users=userDao.findByUser(qu); for(User user: users){ System.out.println(user.getId()+":"+user.getUsername()); } } @Before //在测试方法执行之前执行 public void init()throws Exception { //1.读取配置文件 in = Resources.getResourceAsStream("SqlMapConfig.xml"); //2.创建构建者对象 SqlSessionFactoryBuilder builder = new SqlSessionFactoryBuilder(); //3.创建 SqlSession 工厂对象 factory = builder.build(in); // 4.创建 SqlSession 对象 session = factory.openSession(); //5.创建 Dao 的代理对象 userDao = session.getMapper(IUserDao.class); } @After//在测试方法执行完成之后执行 public void destroy() throws Exception{ session.commit(); //7.释放资源 session.close(); in.close(); } }

4、案例回顾(实体类类型)

4.1、编写IUserDao.java文件

package com.tianyi.dao; import com.tianyi.javabean.QueryUser; import com.tianyi.javabean.User; import java.util.List; public interface IUserDao { List<User> findAll(); }

4.2、编写IUserDao.xml文件

<?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.tianyi.dao.IUserDao"> <!-- 配置查询所有操作 --> <select id="findAll" resultType="com.tianyi.javabean.User"> select * from user </select> </mapper>

4.3、编写MbTest1.java文件

package com.tianyi.test; import com.tianyi.dao.IUserDao; import com.tianyi.javabean.QueryUser; import com.tianyi.javabean.User; 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.After; import org.junit.Before; import org.junit.Test; import java.io.InputStream; import java.util.Date; import java.util.List; public class MbTest1 { private InputStream in ; private SqlSessionFactory factory; private SqlSession session; private IUserDao userDao; @Test public void findAll(){ List<User> users=userDao.findAll(); for(User user: users){ System.out.println(user.getId()+":"+user.getUsername()); } } @Before //在测试方法执行之前执行 public void init()throws Exception { //1.读取配置文件 in = Resources.getResourceAsStream("SqlMapConfig.xml"); //2.创建构建者对象 SqlSessionFactoryBuilder builder = new SqlSessionFactoryBuilder(); //3.创建 SqlSession 工厂对象 factory = builder.build(in); // 4.创建 SqlSession 对象 session = factory.openSession(); //5.创建 Dao 的代理对象 userDao = session.getMapper(IUserDao.class); } @After//在测试方法执行完成之后执行 public void destroy() throws Exception{ session.commit(); //7.释放资源 session.close(); in.close(); } }

5、返回对象属性与表字段不匹配

5.1、重写User.java文件

package com.tianyi.javabean; import java.io.Serializable; import java.util.Date; public class User implements Serializable { private Integer uid; private String uname; private Date ubirthday; private String Sex; private String uaddress; public Integer getUid() { return uid; } public void setUid(Integer uid) { this.uid = uid; } public String getUname() { return uname; } public void setUname(String uname) { this.uname = uname; } public Date getUbirthday() { return ubirthday; } public void setUbirthday(Date ubirthday) { this.ubirthday = ubirthday; } public String getSex() { return Sex; } public void setSex(String sex) { Sex = sex; } public String getUaddress() { return uaddress; } public void setUaddress(String uaddress) { this.uaddress = uaddress; } @Override public String toString() { return "User{" + "uid=" + uid + ", uname='" + uname + '\'' + ", ubirthday=" + ubirthday + ", Sex='" + Sex + '\'' + ", uaddress='" + uaddress + '\'' + '}'; } }

5.2、修改IUserDao.xml文件

<?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.tianyi.dao.IUserDao"> <!-- 配置查询所有操作 --> <select id="findAll" resultType="com.tianyi.javabean.User"> select id as uid,username as uname, birthday as ubirthday,sex as Sex,address as uaddress from user </select> </mapper>
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