一看就懂的Mybatis框架入门笔记

• 本篇为初学Mybatis框架时的入门笔记，整理发出
• Spring集成Mybatis https://www.cnblogs.com/yueshutong/p/9381590.html
• SpringBoot集成Mybatis https://www.cnblogs.com/yueshutong/p/9381590.html

简介

MyBatis 是支持普通 SQL 查询，存储过程和高级映射的优秀持久层框架，其几乎消除了所有的 JDBC 代码和参数的手工设置以及结果集的检索。MyBatis 使用简单的 XML 或注解用于配置和原始映射，将接口和 Java 的 POJOs（Plain Old Java Objects，普通的 Java对象）映射成数据库中的记录。MyBatis 应用程序大都使用 SqlSessionFactory 实例，SqlSessionFactory 实例可以通过 SqlSessionFactoryBuilder 获得，而　SqlSessionFactoryBuilder 则可以从一个 XML 配置文件或者一个预定义的配置类的实例获得。

依赖

mybatis-3.2.2.jar 核心jar
mysql-connector-java-5.1.10-bin.jar 数据库访问

1.Configuration配置

在resources下，新建Configuration.xml

<?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>

    <!-- 设置别名，用于在User.xml中 ，这里不设置
    <typeAliases>
        <typeAlias  alias="User"  type="com.zyzpp.model.User"/>
    </typeAliases>
    -->
    <typeAliases>
        <typeAlias  alias="User"  type="com.zyzpp.model.User"/>
    </typeAliases>
    <environments default="development">
        <environment id="development">
            <transactionManager type="JDBC" />
            <!-- 配置数据库连接信息 -->
            <dataSource type="POOLED">
                <property name="driver" value="com.mysql.jdbc.Driver" />
                <property name="url" value="jdbc:mysql://127.0.0.1:3306/work?useUnicode=true&amp;characterEncoding=UTF-8" />
                <property name="username" value="root" />
                <property name="password" value="123456" />
            </dataSource>
        </environment>
    </environments>

    <!--映射实体的mapper配置-->
    <mappers>
        <mapper resource="com/zyzpp/inter/User.xml"/>
    </mappers>

</configuration>

2.Entity实体类

示例：

package com.zyzpp.model;

public class User {
    private int id;
    private String userName;
    private int userAge;
    private String userAddress;
    private List<Card> cards;

    ....

}

3.Dao层接口

示例：

package com.zyzpp.inter;

public interface IUserOperation {

    public User selectUserByID(int id);
    public List<User> selectUsers(String userName);
    public void addUser(User user);
    public void updateUser(User user);
    public void deleteUser(int id);
    public List<Article> getUserArticles(@Param("userid") int userid);      //多个参数要加注释区分
    public User getUserCards(int id);
    public int getCount(User user);
    public List<User> getLimit(Map map);

}

4.Mapper配置

说白了，就是实现上步接口方法

<?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">
    <!-- 声明接口地址 -->
    <mapper namespace="com.zyzpp.inter.IUserOperation">

    <!-- 如果在配置xml文件中设置了别名，在这里可以只写别名
     <select id="seleteUserByID" parameterType="int" 

     select中包含的是SQL语句，以及语句的参数。
     id 与 接口的方法名一致 parameterType是方法参数类型 -->

    <!-- 根据id查询用户 -->
    <select id="selectUserByID" parameterType="int" resultType="cn.zyzpp.model.User">
        select * from user where id=#{id}
    </select>

    <resultMap type="User" id="resultListUser">
        <id column="id" property="id" jdbcType="INTEGER" />
        <result column="userName" property="userName" jdbcType="VARCHAR" />
        <result column="userAge" property="userAge" jdbcType="INTEGER" />
        <result column="userAddress" property="userAddress" jdbcType="VARCHAR" />
    </resultMap>
    <!-- 根据用户名模糊查找 -->
    <select id="selectUsers" parameterType="String" resultMap="resultListUser">
        select * from user where userName like #{userName}
    </select>

    <!-- 增加一个用户 -->
    <insert id="addUser" parameterType="User" useGeneratedKeys="true"
        keyProperty="id">
        insert into user(userName,userAge,userAddress)
        values(#{userName},#{userAge},#{userAddress})
    </insert>

    <!-- 根据ID更新用户信息 -->
    <update id="updateUser" parameterType="User">
        update user set userName =
        #{userName},userAge=#{userAge},userAddress=#{userAddress} where
        id=#{id}
    </update>

    <!-- 根据id删除用户 -->
    <delete id="deleteUser" parameterType="int">
        delete from user where id=#{id}
    </delete>

    <!-- 其中需要说明的是，如果两个表中存在重名字段，如上文所述uesr表中有id字段，article表中同样有id字段，
    在使用Mybatis进行联合查询的过程中，会遇到只返回一条数据的情况。然而在数据库中直接运行sql语句是正常的。
    在出现重名字段时，配置Mybatis文件时需要把字段重新命名，否则Mybatis会混乱.
    例如下面的 ID一号二号不可以重复。在这里就把article表中的id字段命名为了aid。只可改一号！
     -->
    <!-- User 联合文章进行查询 方法之一的配置 (多对一的方式) column="数据库字段名" property="实体类属性" jdbcType="数据库字段类型" -->
    <resultMap id="resultUserArticleList" type="com.zyzpp.model.Article">
        <id property="id" column="aid" jdbcType="INTEGER" /><!-- id一号 -->
        <result property="title" column="title" />
        <result property="content" column="content" />
        <!-- associayion=标签
        也可以<association property="user" javaType="User" resultMap="resultListUser"/>
        -->
        <association property="user" javaType="User" column="userid">
            <id property="id" column="id" /><!-- id 二号-->
            <result property="userName" column="userName" />
            <result property="userAddress" column="userAddress" />
        </association>
    </resultMap>

    <!-- 多对一 -->
    <select id="getUserArticles" parameterType="int"
        resultMap="resultUserArticleList">
        select user.id,user.userName,user.userAddress,article.id aid,article.title,article.content from user,article
        where
        user.id=article.userid and user.id=#{id}
    </select>

        <!-- 一对多 collection 查询用户手机卡-->
    <resultMap id="resultUserCards" type="com.zyzpp.model.User">
        <id property="id" column="u_id" />
        <result property="userName" column="userName" />
        <result property="userAge" column="userAge" />
        <result property="userAddress" column="userAddress" />
        <collection property="cards" ofType="com.zyzpp.model.Card">
            <id property="id" column="id" />
            <result property="cardNo" column="card_no" />
            <result property="remark" column="remark" />
        </collection>
    </resultMap>

    <!-- 一对多 -->
    <select id="getUserCards" parameterType="int" resultMap="resultUserCards">
        SELECT u.id u_id,u.userName,u.userAge,u.userAddress,c.id,c.card_no,c.remark
        FROM user u,card c
        WHERE u.id=c.user_id AND u.id=#{id}
    </select>

    <!-- 获取总条数 -->
    <select id="getCount" parameterType="com.zyzpp.model.User" resultType="int">
        select count(*) from user
        <where>
            <if test="id!=0"><!-- &quot; " -->
                and id=#{id}
            </if>
            <if test="userName!=null and !&quot;&quot;.equals(userName.trim())">
                and userName like % #{userName} %
            </if>
        </where>
    </select>

    <!-- 获取特定记录-->
    <select id="getLimit" parameterType="java.util.Map" resultMap="resultListUser">
        SELECT * FROM user
        <where>
            <if test="user.id!=0"><!-- &quot; " -->
                and id=#{user.id}
            </if>
            <if test="user.userName!=null and !&quot;&quot;.equals(user.userName.trim())">
                and userName like % #{user.userName} %
            </if>
        </where>
        order by id LIMIT #{page.dbIndex},#{page.dbNumber};
    </select>
</mapper>

5.开始使用

import java.io.Reader;
import org.apache.ibatis.io.Resources;
import org.apache.ibatis.session.SqlSession;
import org.apache.ibatis.session.SqlSessionFactory;
import org.apache.ibatis.session.SqlSessionFactoryBuilder;

public class Test {
    private static SqlSessionFactory sqlSessionFactory;
    private static Reader reader;
    private static String resource = "Configuration.xml";    //mybatis的配置文件

    static{
        try{
            /*使用MyBatis提供的Resources类加载mybatis的配置文件（它也加载关联的映射文件）*/
            reader=Resources.getResourceAsReader(resource);
            sqlSessionFactory = new SqlSessionFactoryBuilder().build(reader);//构建sqlSession的工厂
        }catch (Exception e) {
            e.printStackTrace();
        }
    }

    public static void main(String[] args) {
        Test test =new Test();
        User user=new User();
        test.getLimit();
//      test.getCount(user);
//  test.getUserCards(1);
//  test.getUserArticles(1);
//      test.getUserList("%");
//      test.addUser();
//      test.updateUser(1, "这是更新后的地址");
//      test.deleteUser(3);
    }
    /*
     * 以ID查找单个数据
     */
    public void getUserByID(int id){
        SqlSession session=sqlSessionFactory.openSession();
        try{
        IUserOperation userOperation=session.getMapper(IUserOperation.class);
        User user=userOperation.selectUserByID(id);
        System.out.println("查询ID："+id+"结果如下\n"+"名字："+user.getUserName()+" 年龄："+user.getUserAge()+" 地址："+user.getUserAddress());
        }finally {
            session.close();
        }
    }
    /*
     * 以name查找符合的List列表
     */
    public void getUserList(String userName){
        SqlSession session=sqlSessionFactory.openSession();
        try{
            IUserOperation userOperation=session.getMapper(IUserOperation.class);
            List<User> users = userOperation.selectUsers(userName);
            System.out.println("查询结果如下：");
            for(User user: users){
                System.out.println(user.toString());
            }
        }finally {
            session.close();
        }
    }
    /*
     * 增加一个用户
     */
    public void addUser(){
        User user = new User();
        user.setUserAddress("人民广场");
        user.setUserAge(18);
        user.setUserName("飞鸟");
        SqlSession session = sqlSessionFactory.openSession();
        try{
        IUserOperation userOperation =session .getMapper(IUserOperation.class);
        userOperation.addUser(user);
        session.commit();
        System.out.println("当前增加的用户ID："+user.getId());
        }finally {
            session.close();
        }
    }
    /*
     * 更新数据
     */
    public void updateUser(int id,String content){
        //先得到用户，然后修改提交
        SqlSession session = sqlSessionFactory.openSession();
        try{
            IUserOperation userOperation = session.getMapper(IUserOperation.class);
            User user = userOperation.selectUserByID(id);
            user.setUserAddress(content);
            userOperation.updateUser(user);
            session.commit();
            System.out.println("更新ID："+id+"成功！");
        }finally {
            session.close();
        }
    }
    /*
     * 删除数据
     */
    public void deleteUser(int id){
        SqlSession session = sqlSessionFactory.openSession();
        try{
            IUserOperation userOperation = session.getMapper(IUserOperation.class);
            userOperation.deleteUser(id);
            session.commit();
            System.out.println("删除ID："+id+"成功！");
        }finally {
            session.close();
        }
    }
    /*
     * 多对一
     */
    public void getUserArticles(int userid){
        SqlSession session = sqlSessionFactory.openSession();
        try {
        IUserOperation userOperation=session.getMapper(IUserOperation.class);
        List<Article> articles = userOperation.getUserArticles(userid);
        for(Article article:articles){
        System.out.println("标题："+article.getTitle()+"：内容："+article.getContent()+
        "：作者是："+article.getUser().getUserName()+"：地址："+
        article.getUser().getUserAddress());
        }
        } finally {
        session.close();
        }
        }
    /*
     * 一对多
     */
    private void getUserCards(int userid) {
        SqlSession session = sqlSessionFactory.openSession();
        try {
            IUserOperation userOperation = session.getMapper(IUserOperation.class);
            User user = userOperation.getUserCards(userid);
            System.out.println(user.toString());
            for (Card card : user.getCards()) {
                System.out.println(card.toString());
            }
        } finally {
            session.close();
        }
    }
    /*
     * 按条件查询总条数
     */
    private int getCount(User user){
        SqlSession session = sqlSessionFactory.openSession();
        try {
            IUserOperation userOperation = session.getMapper(IUserOperation.class);
            int i = userOperation.getCount(user);
            System.out.println("总条数："+i);
            return i;
        } finally {
            session.close();
        }
    }
    /**
     * 按条件查询List记录
     */
    private void getLimit(){
        SqlSession session = sqlSessionFactory.openSession();
        try {
            IUserOperation userOperation = session.getMapper(IUserOperation.class);
            Map<String, Object> map=new HashMap<String, Object>();
            Page page=new Page();
            page.setDbIndex(0);
            page.setDbNumber(1);
            User user=new User();
            user.setId(1);
            map.put("page", page);
            map.put("user", user);
            List<User> users = userOperation.getLimit(map);
            System.out.println("查询结果如下：");
            for(User use: users){
                System.out.println(use.toString());
            }
        } finally {
            session.close();
        }
    }
}