• Mybatis学习笔记1


    mybatis是一个orm持久化框架,mybatis专注于sql的操作
    从3.0开始名字改变了:ibatis-mybatis
     对象关系映射(Object Relational Mapping)

    一、Mybatis搭建

    1、导包

    2、mybatis-config.xml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">
    <configuration>
     <environments default="development">
     <environment id="development">
     <transactionManager type="JDBC"/>
     <dataSource type="POOLED"><!-- 四大组件 --><!--池  提高效率管理连接  节省连接过程中消耗的资源 -->
     <property name="driver" value="com.mysql.jdbc.Driver"/>
     <property name="url" value="jdbc:mysql://localhost:3306/crm"/>
     <property name="username" value="root"/>
     <property name="password" value="123456"/>
     </dataSource>
     </environment>
     </environments>
     <mappers><!-- 映射文件  现在不要配 ,有映射文件需要配在这里  包名前面的不要-->
     <mapper resource="com/zy/mapper/UserMapper.xml"/>
     </mappers>
    </configuration>

    3、创建表

    4、创建实体类

    package com.zy.entity;
    
    public class User {
        private Integer uid;
        private String username;
        private String password;
        private String address;
        
        
        public User() {
            super();
            // TODO Auto-generated constructor stub
        }
        
        public User(Integer uid, String username, String password, String address) {
            super();
            this.uid = uid;
            this.username = username;
            this.password = password;
            this.address = address;
        }
    
        public Integer getUid() {
            return uid;
        }
        public void setUid(Integer uid) {
            this.uid = uid;
        }
        public String getUsername() {
            return username;
        }
        public void setUsername(String username) {
            this.username = username;
        }
        public String getPassword() {
            return password;
        }
        public void setPassword(String password) {
            this.password = password;
        }
        public String getAddress() {
            return address;
        }
        public void setAddress(String address) {
            this.address = address;
        }
    
        @Override
        public String toString() {
            return "User [uid=" + uid + ", username=" + username + ", password=" + password + ", address=" + address + "]";
        }
        
    }

    5、搭建映射文件

    UserMapper.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唯一表示此名字下的crud语句
     -->
    <mapper namespace="myuser"><!-- 无规律,起个代号就行,不要重复 -->
     <!-- 提供了增删改查的相关标签 -->
     <!-- 以后的sql都会写在这个配置文件中 -->
     <!--<select id=""></select>
     <insert id=""></insert>
     <delete id=""></delete>
     <update id=""></update>  -->
     
     
     <!-- 查询 -->        <!-- 如果结果是集合也填集合的泛型 -->
     <!-- 
            id:在此命名空间下唯一标识
            resultType:查询结果的返回类型或者集合的泛型
         -->
     <select id="selectUser" resultType="com.zy.entity.User">
     SELECT * FROM t_user
     </select>
     <delete id="deleteUser">
     DELETE FROM t_user WHERE uid=1
     </delete>
     
     <insert id="insertUseer">
    INSERT INTO t_user VALUES(NULL,'bbbb','1234','德国')
     </insert>
     
     <update id="updateUser">
     UPDATE t_user SET username='武磊' WHERE uid=4
     </update>
     
     <!-- 根据id查询用户 -->
     <select id="selectUserByid" resultType="com.zy.entity.User">
     SELECT * FROM t_user WHERE uid=#{id}<!-- 一个参数#{}占位符,里面写什么无所谓 -->
     </select>
     
     <!-- 根据用户名和密码查询用户 -->
     <select id="selectUserByNP" resultType="com.zy.entity.User">
     SELECT * FROM t_user WHERE username=#{uu}  AND password=#{pp}
     </select>
     
     <!-- 特殊字符的转义   <![CDATA[]]>  -->
     <!-- xml把小于号当做标签  在sql语句中直接写小于号会报错 -->
     <!-- The content of elements must consist of well-formed character data or markup. -->
     <select id="selectUser007" resultType="com.zy.entity.User">
     <![CDATA[ SELECT * FROM t_user WHERE uid<9 ]]>
     </select>
     
     <!-- 多条件查询之对象传值  占位符要与对象属性保持一致,不然传不上去 -->
     <insert id="insertUser007">
     INSERT INTO t_user VALUES(NULL,#{username},#{password},#{address})
     
     </insert>
    </mapper>
    <!-- 该实体类与表中列名有不一致的  使用as命别名解决 -->
    <select id="uu" resultType="com.zy.entity.UU">
    SELECT uid id,username name,password,address from t_user
    </select>

    6、在配置文件中引用映射文件

     <mapper resource="com/zy/mapper/UserMapper.xml"/>

    7、得到会话

    package com.zy.test;
    
    import java.io.IOException;
    import java.io.InputStream;
    import java.util.HashMap;
    import java.util.List;
    import java.util.Map;
    
    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 com.zy.entity.User;
    
    public class UserTest {
        public static void main(String[] args) throws Exception {
            //1读取配置文件得到会话工厂
            InputStream resourceAsStream = Resources.getResourceAsStream("mybatis-config.xml");
            //2sql会话工厂创建者
            SqlSessionFactoryBuilder sqlSessionFactoryBuilder = new SqlSessionFactoryBuilder();
            //3生成sql会话工厂
            SqlSessionFactory sf = sqlSessionFactoryBuilder.build(resourceAsStream);
            //4得到mybatis和数据库会话对象
            SqlSession session = sf.openSession();
            
            //完成一个查询任务
    /*//        List<User> selectList = session.selectList("myuser.selectUser");
    //        for (User user : selectList) {
    //            System.out.println(user);
    //        }
            
            //完成一个删除任务(增删改需要提交事务commit)
    //        int delete = session.delete("myuser.deleteUser");
    //        session.commit();//相当于应用改变
            
            //完成一个添加
    //        session.insert("myuser.insertUseer");
    //        session.commit();
            
            
            //完成一个修改
    //        session.update("myuser.updateUser");
    //        session.commit();
            
            //带一个参数的查询
    //        User uu = session.selectOne("myuser.selectUserByid",2);
    //        System.out.println(uu);
            
            //带两个参数的查询
            //解决方案1把参数放对象中   2把参数放map中[map中的键需要与占位符一致]  灵活度更高
    //        Map<Object, Object> map = new HashMap();
    //        map.put("uu", "rose");
    //        map.put("pp", "654321");
    //        
    //        User uu = session.selectOne("myuser.selectUserByNP", map);
    //        System.out.println(uu);
            
            //调用带<号的
    //        List<User> selectList = session.selectList("myuser.selectUser007");
    //        for (User uu : selectList) {
    //            System.out.println(uu);
    //        }
    */        
            //用对象传递参数
            session.insert("myuser.insertUser007",new User(null, "哈哈", "111111", "郑州"));
            session.commit();
        
        }
    
    }

     8、使用mapper代理的方式

    1).在实现的时候,查询字符串,需要namespace.sqlid,容易拼接出错,硬编码
    2).参数是object类型,如果参数传入有问题,在编译的时候不报错
    3).selectOne和seletList还需要判断

    上述写法,有很多吐槽点,所以需要改成主流的方法

    使用mapper代理的方式

    package com.zy.mapper;
    
    import java.util.List;
    
    import com.zy.entity.User;
    
    public interface UserMapper {
        //UserMapper.java接口和UserMapper.xml配套使用----关系密切
        //查询用户
        public List<User> getList();
        
        //根据id删除用户
        public void deleteById(int id);
    
    }
    UserMapper.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="com.zy.mapper.UserMapper">
    <!-- 查询用户 
    1 namespace必须是接口全名称
    2 id名必须和方法名一致
    3 resultType和方法名的返回值保持一致,如果是集合和集合的泛型保持一致
    4 接口和xml名字一致,放在同一包下
    -->
    <select id="getList" resultType="com.zy.entity.User">
    SELECT * FROM t_user 
    </select>
    
    <delete id="deleteById">
    DELETE FROM t_user WHERE uid=#{id}
    </delete>
    </mapper>
    package com.zy.test;
    
    import java.io.IOException;
    import java.io.InputStream;
    import java.util.List;
    
    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 com.zy.entity.User;
    import com.zy.mapper.UserMapper;
    
    public class Test {
    
        public static void main(String[] args) throws Exception {
            //新形势下,使用mapper代理完成调用
            //1读取配置文件得到会话工厂
            InputStream resourceAsStream = Resources.getResourceAsStream("mybatis-config.xml");
            //2sql会话工厂创建者
            SqlSessionFactoryBuilder sqlSessionFactoryBuilder = new SqlSessionFactoryBuilder();
            //3生成sql会话工厂
            SqlSessionFactory sf = sqlSessionFactoryBuilder.build(resourceAsStream);
            //4得到mybatis和数据库会话对象
            SqlSession session = sf.openSession();
            //---------------------------
            //旧的
            //完成一个查询任务
            //        List<User> selectList = session.selectList("myuser.selectUser");
            //        for (User user : selectList) {
            //            System.out.println(user);
            //        }
            //------------------------------------
            
            //新的
            
            //得到一个mapper代理
    //        UserMapper mapper = session.getMapper(UserMapper.class);//反射  UserMapper为接口
    //        //代理调用方法去查询
    //        List<User> list = mapper.getList();
    //        //遍历
    //        for (User user : list) {
    //            System.out.println(user);
    //            
    //        }
            //------------------------
            
            UserMapper mapper = session.getMapper(UserMapper.class);
            mapper.deleteById(4);
            session.commit();
        }
    
    }
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  • 原文地址:https://www.cnblogs.com/qfdy123/p/11284348.html
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