MyBatis 實戰筆記（二）：CRUD 完整配置與 Mapper 代理開發模式

MyBatis 核心配置與 CRUD 實戰

本文承接基礎環境搭建，詳細示範 MyBatis 3.2.x 如何透過 XML 映射檔與 Mapper 介面代理模式，實現資料庫的增刪改查，並解析關鍵配置細節與常見坑點。

一、專案結構與依賴

<dependency>
  <groupId>org.mybatis</groupId>
  <artifactId>mybatis</artifactId>
  <version>3.2.0</version>
</dependency>
<dependency>
  <groupId>mysql</groupId>
  <artifactId>mysql-connector-java</artifactId>
  <version>5.1.22</version>
</dependency>

二、核心配置檔 Configuration.xml

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE configuration PUBLIC "-//mybatis.org//DTD Config 3.0//EN" "https://mybatis.org/dtd/mybatis-3-config.dtd">
<configuration>
  <typeAliases>
    <typeAlias alias="User" type="com.yihaomen.mybatis.model.User"/>
  </typeAliases>

  <environments default="development">
    <environment id="development">
      <transactionManager type="JDBC"/>
      <dataSource type="POOLED">
        <property name="driver" value="com.mysql.jdbc.Driver"/>
        <property name="url" value="jdbc:mysql://192.168.6.1:3306/test"/>
        <property name="username" value="dev"/>
        <property name="password" value="123qwe"/>
      </dataSource>
    </environment>
  </environments>

  <mappers>
    <mapper resource="com/yihaomen/mybatis/model/User.xml"/>
  </mappers>
</configuration>

重點：typeAlias 為實體類定義別名，映射檔中 resultType 直接使用別名；POOLED 資料源內建連線池。

三、實體類與映射檔 User.xml

實體類 User.java

public class User {
    private int id;
    private String userName;
    private int userAge;
    private String userAddress;
    // getter/setter 省略
}

映射檔完整配置

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN" "https://mybatis.org/dtd/mybatis-3-mapper.dtd">
<mapper namespace="com.yihaomen.mybatis.dao.IUserOperation">

  <select id="selectUserByID" parameterType="int" resultType="User">
    select * from `user` where id = #{id}
  </select>

  <insert id="addUser" parameterType="User" useGeneratedKeys="true" keyProperty="id">
    insert into user(userName,userAge,userAddress) values(#{userName},#{userAge},#{userAddress})
  </insert>

  <update id="updateUser" parameterType="User">
    update user set userName=#{userName},userAge=#{userAge},userAddress=#{userAddress} where id=#{id}
  </update>

  <delete id="deleteUser" parameterType="int">
    delete from user where id=#{id}
  </delete>

  <select id="list" resultType="User">
    select * from `user`
  </select>

  <select id="findUserByName" parameterType="String" resultType="User">
    select * from `user` where username like '%${value}%'
  </select>

</mapper>

關鍵屬性解析

• useGeneratedKeys="true" keyProperty="id"：MySQL 自增主鍵回填。
• #{}：預編譯佔位符，防 SQL 注入，支援 POJO/Map/簡單型別（OGNL 存取屬性）。
• ${}：字串拼接，**易導致 SQL 注入**，僅用於動態表名/欄位名或 LIKE '%${value}%' 此類無法用預編譯場景。
• parameterType：輸入參數型別；resultType：單條結果映射型別。

四、Mapper 介面代理開發模式

定義介面 IUserOperation，**介面全限定名 = namespace**，**方法名 = statement id**，即可透過 session.getMapper(IUserOperation.class) 獲得代理實現，完全免寫 session.selectOne("namespace.id", param) 硬編碼字串。

public interface IUserOperation {
    User selectUserByID(int id);
    void addUser(User user);
    void updateUser(User user);
    void deleteUser(int id);
    List<User> list();
    List<User> findUserByName(String name);
}

五、測試類與執行日誌

public class Test {
    private static SqlSessionFactory sqlSessionFactory;
    static {
        Reader reader = Resources.getResourceAsReader("Configuration.xml");
        sqlSessionFactory = new SqlSessionFactoryBuilder().build(reader);
    }

    public void geFindUserByName(String name) {
        try (SqlSession session = sqlSessionFactory.openSession()) {
            IUserOperation op = session.getMapper(IUserOperation.class);
            List<User> list = op.findUserByName(name);
            System.out.println("匹配筆數：" + list.size());
        }
    }
    // 其他 CRUD 方法類似，均使用 try-with-resources 自動關閉 session
}

日誌輸出範例：

DEBUG - ==> Preparing: select * from `user` where username like '%小%'
DEBUG - ==> Parameters:
DEBUG - <== Total: 7

六、核心知識點總結

後續將介紹動態 SQL、關聯映射、緩存機制與 Spring 整合，敬請期待。