Mybatis项目构建和CURD操作

Mybatis入门

一、使用SqlSession对象创建Dao接口代理对象进行持久化操作

1、使用maven构建java项目

2、修改pom.xml配置，添加所需jar包坐标

 <?xml version="1.0" encoding="UTF-8"?>
 <project xmlns="http://maven.apache.org/POM/4.0.0"
          xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
          xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
     <modelVersion>4.0.0</modelVersion>

     <groupId>sun</groupId>
     <artifactId>mybatis05crud</artifactId>
     <version>1.0-SNAPSHOT</version>
     <packaging>jar</packaging>

     <dependencies>
         <dependency>
             <groupId>org.mybatis</groupId>
             <artifactId>mybatis</artifactId>
             <version>3.4.5</version>
         </dependency>

         <dependency>
             <groupId>mysql</groupId>
             <artifactId>mysql-connector-java</artifactId>
             <version>5.1.6</version>
         </dependency>

         <dependency>
             <groupId>junit</groupId>
             <artifactId>junit</artifactId>
             <version>4.12</version>
         </dependency>

         <dependency>
             <groupId>log4j</groupId>
             <artifactId>log4j</artifactId>
             <version>1.2.17</version>
         </dependency>
     </dependencies>

 </project>

3、在src/main/java下创建实体类和dao接口

实体类：

 package sun.domain;

 import java.io.Serializable;
 import java.util.Date;

 public class User implements Serializable {
     private Integer id;
     private String username;
     private Date birthday;
     private String sex;
     private String address;

     public Integer getId() {
         return id;
     }

     public void setId(Integer id) {
         this.id = id;
     }

     public String getUsername() {
         return username;
     }

     public void setUsername(String username) {
         this.username = username;
     }

     public Date getBirthday() {
         return birthday;
     }

     public void setBirthday(Date birthday) {
         this.birthday = birthday;
     }

     public String getSex() {
         return sex;
     }

     public void setSex(String sex) {
         this.sex = sex;
     }

     public String getAddress() {
         return address;
     }

     public void setAddress(String address) {
         this.address = address;
     }

     @Override
     public String toString() {
         return "User{" +
                 "id=" + id +
                 ", username='" + username + '\'' +
                 ", birthday=" + birthday +
                 ", sex='" + sex + '\'' +
                 ", address='" + address + '\'' +
                 '}';
     }
 }

Dao接口：

 package sun.dao;

 import sun.domain.QueryObj;
 import sun.domain.User;

 import java.util.List;

 public interface UserDao {
     /**
      * 查询所有用户
      * @return
      */
     List<User> findAll();

     /**
      * 创建用户
      */
     void saveUser(User user);

     /**
      * 更新用户
      */
     void updateUser(User user);

     /**
      * 删除用户
      */
     void deleteUser(Integer userId);

     /**
      * 查询用户（根据ID）
      */
     User findUserById(Integer userId);

     /**
      * 模糊查询
      */
     List<User> findUserByName(String name);

     /**
      * 查询总用户数
      */
     int getCount();

     /**
      * 模糊查询
      */
     List<User> findUserByQueryObj(QueryObj qobj);
 }

4、在src/main/resources下创建SqlMapConfig.xml（Mybatis的主配置文件）

 <?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">

 <!--mybatis主配置文件-->
 <configuration>
     <!--配置环境-->
     <environments default="mysql">
         <!--配置mysql环境-->
         <environment id="mysql">
             <!--配置事务类型-->
             <transactionManager type="JDBC"></transactionManager>
             <!--配置数据库连接池-->
             <dataSource type="POOLED">
                 <!--配置连接数据库的四个基本信息-->
                 <property name="driver" value="com.mysql.jdbc.Driver"></property>
                 <property name="url" value="jdbc:mysql://localhost:3306/javatest"></property>
                 <property name="username" value="root"></property>
                 <property name="password" value="root"></property>
             </dataSource>

         </environment>
     </environments>

     <!--指定映射配置文件位置-->
     <mappers>
         <mapper resource="sun/dao/UserDao.xml"></mapper>
     </mappers>
 </configuration>

5、src/main/resources下创建和Dao接口同名，同包路径的xml映射配置文件

 <?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="sun.dao.UserDao">

     <!--查询所有-->
     <select id="findAll" resultType="sun.domain.User">
         SELECT * from user;
     </select>
     <!--创建用户-->
     <insert id="saveUser" parameterType="sun.domain.User">
         <selectKey keyProperty="id" keyColumn="id" resultType="int" order="AFTER">
             SELECT last_insert_id();
         </selectKey>
         insert into user(username,birthday,sex,address) VALUES(#{username},#{birthday},#{sex},#{address});
     </insert>
     <!--更新用户-->
     <update id="updateUser" parameterType="sun.domain.User">
         update user set username=#{username},birthday=#{birthday},sex=#{sex},address=#{address} where id=#{id};
     </update>
     <!--删除用户-->
     <delete id="deleteUser" parameterType="java.lang.Integer">
         delete from user where id=#{id};
     </delete>
     <!--根据id查询用户-->
     <select id="findUserById" parameterType="int" resultType="sun.domain.User">
         SELECT * from user where id=#{id};
     </select>
     <!--模糊查询-->
     <select id="findUserByName" parameterType="String" resultType="sun.domain.User">
         SELECT * from user where username like #{username};
     </select>
     <!--获取总记录数-->
     <select id="getCount" resultType="int">
         SELECT count(1) from user;
     </select>
     <!--模糊查询-->
     <select id="findUserByQueryObj" parameterType="sun.domain.QueryObj" resultType="sun.domain.User">
         SELECT * from user where username like #{user.username};
     </select>
 </mapper>

6、在test目录下创建test测试类

 package sun.test;

 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 sun.dao.UserDao;
 import sun.domain.QueryObj;
 import sun.domain.User;

 import java.io.IOException;
 import java.io.InputStream;
 import java.util.Date;
 import java.util.List;

 public class MybatisTest {

     private InputStream in;
     private SqlSession sqlSession;
     private UserDao userDao;

     @Before
     public void init() throws IOException {
         // 读取配置文件
         in = Resources.getResourceAsStream("SqlMapConfig.xml");
         // 创建SqlSessionFactory
         SqlSessionFactoryBuilder builder = new SqlSessionFactoryBuilder();
         SqlSessionFactory factory = builder.build(in);
         // 使用工厂生产sqlsession对象
         sqlSession = factory.openSession();
         // 使用sqlsession创建UserDao接口代理对象
         userDao = sqlSession.getMapper(UserDao.class);
     }

     @After
     public void destory() throws IOException {
         sqlSession.commit();
         sqlSession.close();
         in.close();
     }

     @Test
     public void findAllTest() {
         // 使用代理对象执行方法
         List<User> all = userDao.findAll();
         for (User user : all) {
             System.out.println(user);
         }
     }

     @Test
     public void saveUserTest() {
         User user = new User();
         user.setUsername("kelvin");
         user.setBirthday(new Date());
         user.setSex("男");
         user.setAddress("安徽省宿州市");
         System.out.println(user);
         userDao.saveUser(user);
         System.out.println(user);
     }

     @Test
     public void updateUserTest() {
         User user = new User();
         user.setId(50);
         user.setUsername("sun");
         user.setBirthday(new Date());
         user.setSex("男");
         user.setAddress("安徽省宿州市");
         userDao.updateUser(user);
     }

     @Test
     public void deleteUserTest(){
         userDao.deleteUser(50);
     }

     @Test
     public void findUserById(){
         User user = userDao.findUserById(48);
         System.out.println(user);
     }
     @Test
     public void findUserByName(){
         List<User> userByName = userDao.findUserByName("%王%");
         for (User user : userByName) {
             System.out.println(user);
         }
     }
     @Test
     public void findUserByQueryObj(){
         QueryObj queryObj = new QueryObj();
         User user1 = new User();
         user1.setUsername("%王%");
         queryObj.setUser(user1);
         List<User> userByName = userDao.findUserByQueryObj(queryObj);
         for (User user : userByName) {
             System.out.println(user);
         }
     }

     @Test
     public void getCountTest(){
         int count = userDao.getCount();
         System.out.println(count);
     }
 }

7、数据库表结构如图

操作中遇到的问题及解决办法

1、在执行增删改的操作中，测试未报错但数据库中数据未生效？
答：在使用Mybatis执行增删改时，AutoCommit会设置为false，所以如果没有手动添加sqlSession.commit()时增删改操作会触发事务回滚导致操作未生效。

2、如果实现类和表中字段名称不一致，查询后不能正确将查询结果封装为指定对象如何解决？
答：方法一、可以在映射配置文件的sql语句中将查询后的字段重命名为实体类中的字段。该方式是在sql语句上对该问题进行解决，因此效率较高，但是每一个查询语句都要对字段进行修改别名操作比较繁琐。
　　方法二、可以再映射配置文件mapper内部添加下列内容，在每一个查询操作中将属性resultType="全类名"改为resultMap="resultMap的id属性名"，对于resultMap中的property为实体类中字段，column为数据库表字段。该方式在加载配置文件时需要多加载resultMap项，但是在mapper内的所有查询操作中只需配置属性，不需要对查询sql语句进行修改，操作简便。

 <resultMap id="userMap" type="sun.domain.User">
         <!--主键字段对应-->
         <id property="user_id" column="id"></id>
         <!--非主键关系对应-->
         <result property="user_name" column="username"></result>
         <result property="user_birthday" column="birthday"></result>
         <result property="user_address" column="address"></result>
         <result property="user_sex" column="sex"></result>
 </resultMap>

3、在映射配置文件中，#{ }和${ }的区别的什么？

答：#{ } 预编译后使用PrepareStatement的？占位，而${ }使用Statement对象直接将参数和sql语句拼接成字符串然后在进行编译。

二、使用Dao实现类实现持久化操作

对比使用SqlSession创建代理对象方式有两处改变

1、在dao包下创建dao实现类

 package sun.dao.impl;

 import org.apache.ibatis.session.SqlSession;
 import org.apache.ibatis.session.SqlSessionFactory;
 import sun.dao.UserDao;
 import sun.domain.User;

 import java.util.List;

 /**
  * @Classname UserDaoImpl
  * @Description TODO
  * @Date 2020/9/10 10:15
  * @Created by Administrator
  */
 public class UserDaoImpl implements UserDao {
     private SqlSessionFactory sqlSessionFactory;

     public UserDaoImpl(SqlSessionFactory sqlSessionFactory) {
         this.sqlSessionFactory = sqlSessionFactory;
     }

     public List<User> findAll() {
         SqlSession sqlSession = sqlSessionFactory.openSession();
         List<User> users = sqlSession.selectList("sun.dao.UserDao.findAll");
         sqlSession.commit();
         sqlSession.close();
         return users;
     }

     public void saveUser(User user) {
         SqlSession sqlSession = sqlSessionFactory.openSession();
         int insert = sqlSession.insert("sun.dao.UserDao.saveUser", user);
         sqlSession.commit();
         sqlSession.close();
     }

     public void updateUser(User user) {
         SqlSession sqlSession = sqlSessionFactory.openSession();
         int update = sqlSession.update("sun.dao.UserDao.updateUser", user);
         sqlSession.commit();
         sqlSession.close();
     }

     public void deleteUser(Integer userId) {
         SqlSession sqlSession = sqlSessionFactory.openSession();
         int delete = sqlSession.delete("sun.dao.UserDao.deleteUser", userId);
         sqlSession.commit();
         sqlSession.close();
     }

     public User findUserById(Integer userId) {
         SqlSession sqlSession= sqlSessionFactory.openSession();
         User user = sqlSession.selectOne("sun.dao.UserDao.findUserById", userId);
         sqlSession.commit();
         sqlSession.close();
         return user;
     }

     public List<User> findUserByName(String name) {
         SqlSession sqlSession = sqlSessionFactory.openSession();
         List<User> users = sqlSession.selectList("sun.dao.UserDao.findUserByName", name);
         sqlSession.commit();
         sqlSession.close();
         return users;
     }

     public int getCount() {
         SqlSession sqlSession = sqlSessionFactory.openSession();
         int count = sqlSession.selectOne("sun.dao.UserDao.getCount");
         return count;
     }
 }

2、测试类

 package sun.test;

 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 sun.dao.UserDao;
 import sun.dao.impl.UserDaoImpl;
 import sun.domain.User;

 import java.io.IOException;
 import java.io.InputStream;
 import java.util.Date;
 import java.util.List;

 public class MybatisTest {

     private InputStream in;
     private UserDaoImpl userDao;

     @Before
     public void init() throws IOException {
         // 读取配置文件
         in = Resources.getResourceAsStream("SqlMapConfig.xml");
         // 创建SqlSessionFactory
         SqlSessionFactoryBuilder builder = new SqlSessionFactoryBuilder();
         SqlSessionFactory factory = builder.build(in);

         userDao = new UserDaoImpl(factory);
     }

     @After
     public void destory() throws IOException {
         in.close();
     }

     @Test
     public void findAllTest() {
         // 使用代理对象执行方法
         List<User> all = userDao.findAll();
         for (User user : all) {
             System.out.println(user);
         }
     }

     @Test
     public void saveUserTest() {
         User user = new User();
         user.setUsername("kelvin");
         user.setBirthday(new Date());
         user.setSex("男");
         user.setAddress("安徽省宿州市");
         System.out.println(user);
         userDao.saveUser(user);
         System.out.println(user);
     }

     @Test
     public void updateUserTest() {
         User user = new User();
         user.setId(54);
         user.setUsername("sun");
         user.setBirthday(new Date());
         user.setSex("男");
         user.setAddress("安徽省宿州市");
         userDao.updateUser(user);
     }

     @Test
     public void deleteUserTest(){
         userDao.deleteUser(54);
     }

     @Test
     public void findUserById(){
         User user = userDao.findUserById(48);
         System.out.println(user);
     }
     @Test
     public void findUserByName(){
         List<User> userByName = userDao.findUserByName("%王%");
         for (User user : userByName) {
             System.out.println(user);
         }
     }

     @Test
     public void getCountTest(){
         int count = userDao.getCount();
         System.out.println(count);
     }
 }