MyBatis Generator 逆向工程實戰：從數據庫到代碼的全自動化生成

為什麼需要 MyBatis Generator？

手寫 Entity、Mapper 接口、XML 映射文件重複枯燥且易出錯。MyBatis Generator (MBG) 通過讀取數據庫元數據，自動生成：

• POJO (Entity)：含字段、Getter/Setter、構造器、toString
• Mapper 接口：CRUD 方法（insert/updateByPrimaryKey/selectByExample 等）
• Mapper XML：SQL 語句、resultMap、動態 where 條件
• Example 類：類型安全的動態查詢構建器（Criteria 鏈式調用）

Maven 整合配置

1. 插件依賴

<plugin>
    <groupId>org.mybatis.generator</groupId>
    <artifactId>mybatis-generator-maven-plugin</artifactId>
    <version>1.4.2</version>
    <configuration>
        <configurationFile>src/main/resources/generatorConfig.xml</configurationFile>
        <verbose>true</verbose>
        <overwrite>true</overwrite>
    </configuration>
    <dependencies>
        <dependency><groupId>mysql</groupId><artifactId>mysql-connector-java</artifactId><version>8.0.33</version></dependency>
        <dependency><groupId>org.mybatis.generator</groupId><artifactId>mybatis-generator-core</artifactId><version>1.4.2</version></dependency>
    </dependencies>
</plugin>

2. generatorConfig.xml 核心配置

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE generatorConfiguration PUBLIC "-//mybatis.org//DTD MyBatis Generator Configuration 1.0//EN" "https://mybatis.org/dtd/mybatis-generator-config_1_0.dtd">
<generatorConfiguration>
    <properties resource="jdbc.properties"/>
    <classPathEntry location="${jdbc.driverLocation}"/>

    <context id="default" targetRuntime="MyBatis3">
        <commentGenerator>
            <property name="suppressDate" value="true"/>
            <property name="suppressAllComments" value="true"/>
        </commentGenerator>

        <jdbcConnection driverClass="${jdbc.driverClass}"
                        connectionURL="${jdbc.url}"
                        userId="${jdbc.user}"
                        password="${jdbc.password}">
        </jdbcConnection>

        <javaTypeResolver><property name="forceBigDecimals" value="false"/></javaTypeResolver>

        <javaModelGenerator targetPackage="com.example.demo.entity" targetProject="src/main/java">
            <property name="enableSubPackages" value="false"/>
            <property name="constructorBased" value="true"/>
            <property name="trimStrings" value="true"/>
        </javaModelGenerator>

        <sqlMapGenerator targetPackage="com.example.demo.mapper.xml" targetProject="src/main/resources">
            <property name="enableSubPackages" value="false"/>
        </sqlMapGenerator>

        <javaClientGenerator type="XMLMAPPER" targetPackage="com.example.demo.mapper" targetProject="src/main/java">
            <property name="enableSubPackages" value="false"/>
        </javaClientGenerator>

        <table tableName="user" domainObjectName="User">
            <generatedKey column="id" sqlStatement="MySQL" identity="true"/>
        </table>
        <!-- 多表可配置多個 table 節點，或用 tableName="%" 生成全部 -->
    </context>
</generatorConfiguration>

3. jdbc.properties

jdbc.driverLocation=/path/to/mysql-connector-java-8.0.33.jar
jdbc.driverClass=com.mysql.cj.jdbc.Driver
jdbc.url=jdbc:mysql://localhost:3306/demo?useSSL=false&serverTimezone=UTC&characterEncoding=utf8
jdbc.user=root
jdbc.password=123456

IDEA 一鍵運行

1. Maven 面板 → Plugins → mybatis-generator → mybatis-generator:generate
2. 或 Run Configuration → Maven → Command: mybatis-generator:generate -e

實戰場景：Example 動態查詢最佳實踐

場景一：多條件精確刪除

public int deleteUserApply(Long userId, Long teamId) {
    UserApplyExample example = new UserApplyExample();
    example.createCriteria()
           .andUserIdEqualTo(userId)
           .andTeamIdEqualTo(teamId);
    return userApplyMapper.deleteByExample(example);
}

場景二：非主鍵更新（樂觀鎖版本控制）

public int updateTeamScore(TeamInfo team) {
    TeamInfoExample example = new TeamInfoExample();
    example.createCriteria().andTeamIdEqualTo(team.getTeamId());
    // updateByExampleSelective 僅更新非 null 字段
    return teamInfoMapper.updateByExampleSelective(team, example);
}

場景三：模糊查詢 + 排序 + 分頁

public List<TeamInfo> searchByName(String name, int page, int size) {
    TeamInfoExample example = new TeamInfoExample();
    example.createCriteria().andTeamNameLike("%" + name + "%").andEnableEqualTo((short)1);
    example.setOrderByClause("team_score DESC, create_time ASC");
    example.setOffset((page - 1) * size);
    example.setLimit(size);
    return teamInfoMapper.selectByExample(example);
}

場景四：範圍查詢（分數區間）

public TeamLevel getLevelByScore(long score) {
    TeamLevelExample example = new TeamLevelExample();
    example.createCriteria()
           .andNeedScoreLessThanOrEqualTo(score)
           .andUpScoreGreaterThan(score);
    List<TeamLevel> list = teamLevelMapper.selectByExample(example);
    return list.isEmpty() ? null : list.get(0);
}

進階技巧與避坑

總結

MyBatis Generator 將「數據庫 Schema → Java 代碼」的機械勞動自動化，配合 Example 動態查詢，極大提升開發效率。掌握 generatorConfig.xml 核心節點配置、主鍵策略映射、Example 靈活用法，即可在項目中穩定落地逆向工程流程。