MyBatis 完整教程：從入門到進階——CRUD、關聯查詢、動態 SQL、緩存、Spring 整合實戰

MyBatis 簡介

MyBatis 是優秀的持久層框架，支持普通 SQL、存儲過程、高級映射。消除幾乎所有 JDBC 代碼、手工設置參數、結果集封裝。可用 XML 或註解配置映射，將接口與 POJO 映射為數據庫記錄。

定位：JDBC → DbUtils → MyBatis → Hibernate（半自動 ORM，SQL 可控）

快速入門：7 步構建第一個查詢

1. 新建 Java 項目，導入 mybatis-3.x.jar、mysql-connector-java.jar
2. 建表 users(id, name, age) 插入測試數據
3. 配置 conf.xml：數據源、事務管理器、環境
4. 定義實體類 User
5. 編寫 userMapper.xml：<select id="getUser" parameterType="int" resultType="User">select * from users where id=#{id}</select>
6. conf.xml 註冊 mapper：<mapper resource=".../userMapper.xml"/>
7. 測試代碼：SqlSessionFactory → SqlSession → selectOne(statement, 1)

CRUD 完整映射（XML 風格）

<insert id="insertUser" parameterType="User">
    insert into users(name, age) values(#{name}, #{age})
</insert>

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

<update id="updateUser" parameterType="User">
    update users set name=#{name}, age=#{age} where id=#{id}
</update>

<select id="selectUser" parameterType="int" resultType="User">
    select * from users where id=#{id}
</select>

<select id="selectAllUsers" resultType="User">
    select * from users
</select>

註解風格映射

public interface UserMapper {
    @Insert("insert into users(name, age) values(#{name}, #{age})")
    int insertUser(User user);
    
    @Delete("delete from users where id=#{id}")
    int deleteUserById(int id);
    
    @Update("update users set name=#{name}, age=#{age} where id=#{id}")
    int updateUser(User user);
    
    @Select("select * from users where id=#{id}")
    User getUserById(int id);
    
    @Select("select * from users")
    List<User> getAllUser();
}

conf.xml 註冊：<mapper class="...UserMapper"/>

優化配置三板斧

字段與屬性名不一致解決方案

-- 表 orders(order_id, order_no, order_price)
-- 實體 Order(id, orderNo, price)

-- 方式一：SQL 別名
<select id="selectOrder" resultType="_Order">
    select order_id id, order_no orderNo, order_price price from orders where order_id=#{id}
</select>

-- 方式二：resultMap 映射
<select id="selectOrder" resultMap="orderResultMap">
    select * from orders where order_id=#{id}
</select>
<resultMap type="_Order" id="orderResultMap">
    <id property="id" column="order_id"/>
    <result property="orderNo" column="order_no"/>
    <result property="price" column="order_price"/>
</resultMap>

關聯查詢：一對一、一對多

一對一：班級-老師

<!-- 嵌套結果：單次連表查詢 -->
<resultMap type="_Classes" id="classResultMap">
    <id property="id" column="c_id"/>
    <result property="name" column="c_name"/>
    <association property="teacher" javaType="_Teacher">
        <id property="id" column="t_id"/>
        <result property="name" column="t_name"/>
    </association>
</resultMap>

<!-- 嵌套查詢：分步查詢，支持延遲加載 -->
<resultMap type="_Classes" id="classResultMap2">
    <association property="teacher" column="teacher_id" select="getTeacher"/>
</resultMap>
<select id="getTeacher" parameterType="int" resultType="_Teacher">
    select t_id id, t_name name from teacher where t_id=#{id}
</select>

一對多：班級-學生

<collection property="students" ofType="_Student">
    <id property="id" column="s_id"/>
    <result property="name" column="s_name"/>
</collection>
-- 嵌套查詢版
<collection property="students" column="c_id" ofType="_Student" select="getStudents"/>

動態 SQL 與模糊查詢

<select id="getUser" parameterType="ConditionUser" resultType="User">
    select * from d_user where age >= #{minAge} and age <= #{maxAge}
    <if test='name != null and name != ""'>
        and name like #{name}
    </if>
</select>

常用標籤：<if>、<choose/when/otherwise>、<trim>、<where>、<set>、<foreach>

調用存儲過程

<select id="getCount" statementType="CALLABLE" parameterMap="getCountMap">
    call mybatis.get_user_count(?,?)
</select>
<parameterMap type="Map" id="getCountMap">
    <parameter property="sex_id" mode="IN" jdbcType="INTEGER"/>
    <parameter property="user_count" mode="OUT" jdbcType="INTEGER"/>
</parameterMap>

緩存機制

<cache eviction="FIFO" flushInterval="60000" size="512" readOnly="true"/>

Spring 整合 MyBatis 完整配置

核心依賴

mybatis-spring, spring-jdbc, spring-tx, spring-context, spring-test, mysql-connector

beans.xml 關鍵 Bean

<!-- 1. 數據源 -->
<bean id="dataSource" class="org.springframework.jdbc.datasource.DriverManagerDataSource">
    <property name="driverClassName" value="com.mysql.jdbc.Driver"/>
    <property name="url" value="jdbc:mysql://localhost:3306/mybatis"/>
    <property name="username" value="root"/>
    <property name="password" value="root"/>
</bean>

<!-- 2. SqlSessionFactory -->
<bean id="sqlSessionFactory" class="org.mybatis.spring.SqlSessionFactoryBean">
    <property name="dataSource" ref="dataSource"/>
    <property name="typeAliasesPackage" value="com.domain"/>
</bean>

<!-- 3. Mapper 掃描器 -->
<bean class="org.mybatis.spring.mapper.MapperScannerConfigurer">
    <property name="basePackage" value="com.mapper"/>
    <property name="sqlSessionFactory" ref="sqlSessionFactory"/>
</bean>

<!-- 4. 事務管理 -->
<bean id="txManager" class="org.springframework.jdbc.datasource.DataSourceTransactionManager">
    <property name="dataSource" ref="dataSource"/>
</bean>
<tx:annotation-driven transaction-manager="txManager"/>

DAO 接口 + Mapper.xml 同名同包

public interface UserMapper {
    void save(User user);
    User findById(int id);
    List<User> findAll();
}

<mapper namespace="com.mapper.UserMapper">
    <resultMap id="userResult" type="User">...</resultMap>
    <insert id="save" keyColumn="user_id" keyProperty="id" useGeneratedKeys="true">...</insert>
    <select id="findById" resultMap="userResult">...</select>
    <select id="findAll" resultMap="userResult">...</select>
</mapper>

測試類

@RunWith(SpringJUnit4ClassRunner.class)
@ContextConfiguration("/beans.xml")
public class SMTest {
    @Autowired UserMapper userMapper;
    @Test public void save() { ... }
    @Test public void findAll() { ... }
}

總結

MyBatis 以「SQL 可控、映射靈活、學習曲線平緩」著稱。掌握 resultMap 解決字段映射、association/collection 處理關聯、動態 SQL 構建複雜查詢、一二級緩存優化性能、Spring 整合實現聲明式事務，即可應對絕多數企業級持久層開發需求。