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项目初始化.md">13. 项目初始化.md</a></li></ul></li></ul></aside><main class="vp-page"><div class="theme-default-content"><div><p>大家学习中如果碰到困难，可以加入**<a href="https://b11et3un53m.feishu.cn/wiki/M9LKwYAlHiZoyhkB5iKcgOh1nmc" target="_blank" rel="noopener noreferrer">黑马智学伴侣</a>**寻求帮助，有学习交流群，老师、同学在线答疑。还有独享的企业级项目，避免与人撞车。</p><p>本篇学习文档对应B站视频：</p><p>暂时无法在飞书文档外展示此内容</p><p>大家在日常开发中应该能发现，单表的CRUD功能代码重复度很高，也没有什么难度。而这部分代码量往往比较大，开发起来比较费时。</p><p>因此，目前企业中都会使用一些组件来简化或省略单表的CRUD开发工作。目前在国内使用较多的一个组件就是MybatisPlus.</p><p>官方网站如下：</p><p>暂时无法在飞书文档外展示此内容</p><p>当然，MybatisPlus不仅仅可以简化单表操作，而且还对Mybatis的功能有很多的增强。可以让我们的开发更加的简单，高效。</p><p>通过今天的学习，我们要达成下面的目标：</p><ul><li>能利用MybatisPlus实现基本的CRUD</li><li>会使用条件构建造器构建查询和更新语句</li><li>会使用MybatisPlus中的常用注解</li><li>会使用MybatisPlus处理枚举、JSON类型字段</li><li>会使用MybatisPlus实现分页</li></ul><h1 id="_1-快速入门" tabindex="-1"><a class="header-anchor" href="#_1-快速入门"><span><strong>1.快速入门</strong></span></a></h1><p>为了方便测试，我们先创建一个新的项目，并准备一些基础数据。</p><h2 id="_1-1-环境准备" tabindex="-1"><a class="header-anchor" href="#_1-1-环境准备"><span><strong>1.1.环境准备</strong></span></a></h2><p>复制课前资料提供好的一个项目到你的工作空间（不要包含空格和特殊字符）：</p><p><img src="https://b11et3un53m.feishu.cn/space/api/box/stream/download/asynccode/?code=ZmQxZDMyNTEyYWMxOTZlODY2MmEwMDExYjRhZDY1MGNfVVFnY1VDS2oxWHliUTUzWHV1MFV1R3VhRXBjeTMzVUhfVG9rZW46TmU0M2JNbkFVbzZIekl4Z1RrYmNEYmFsblJiXzE3NDg3OTM4MzU6MTc0ODc5NzQzNV9WNA" alt="img"></p><p>然后用你的IDEA工具打开，项目结构如下：</p><p><img src="https://b11et3un53m.feishu.cn/space/api/box/stream/download/asynccode/?code=MWQ3Y2U3ZTJmMTU3YTAwMzA0ODgyNTFjYjdlNTY0MjJfU3VHVEppQWFOZVVXdzhEYXZrUFp2bGgxUVRicklrQ2dfVG9rZW46WjhOSmJOMUp5bzFqeEt4R2xvTmN3R1JHbk5mXzE3NDg3OTM4MzU6MTc0ODc5NzQzNV9WNA" alt="img"></p><p>注意配置一下项目的JDK版本为JDK11。首先点击项目结构设置：</p><p><img src="https://b11et3un53m.feishu.cn/space/api/box/stream/download/asynccode/?code=OGZhNjM2M2U4Zjk2NTc5ODk5YjhlZWJjZDQ3MDRkYzVfN0tvVkliVUE2Wk9Va0xDWUhSQ0ZPNHNSbGhGQXZPcHBfVG9rZW46TXV2ZmJKQlJwb1pCbHl4Zkt3eGNLdDRrbkpoXzE3NDg3OTM4MzU6MTc0ODc5NzQzNV9WNA" alt="img"></p><p>在弹窗中配置JDK：</p><p><img src="https://b11et3un53m.feishu.cn/space/api/box/stream/download/asynccode/?code=ZjU4NzE5NTI0ZmY4NjlhNzI5MzFhOWI4OTVlZmJjOTRfV0FpR2lMVXdualZ3OGEybGxraXRBRjRSbTVlTDRYcVRfVG9rZW46TEVRbWJ0UVR4b0s0eld4SDRyRWNFd1dIbnFoXzE3NDg3OTM4MzU6MTc0ODc5NzQzNV9WNA" alt="img"></p><p>接下来，要导入两张表，在课前资料中已经提供了SQL文件：</p><p><img src="https://b11et3un53m.feishu.cn/space/api/box/stream/download/asynccode/?code=ZTUzOTBhMjkxYzc2YzUzODRlODIzZWIzNGRkYTNmY2VfZ0N6Y0J3Sk1VWUFhT2FabjRKTmpyajJCelA5Zk9nZWJfVG9rZW46WTNvN2JQZ0c4b0ZNQmt4MlVuVmNlZm9lblNkXzE3NDg3OTM4MzU6MTc0ODc5NzQzNV9WNA" alt="img"></p><p>对应的数据库表结构如下：</p><p><img src="https://b11et3un53m.feishu.cn/space/api/box/stream/download/asynccode/?code=OGRjOTZhZTVjZTRmYzc1YWRhOGQzNzUzNjJlYTM3N2FfTkdtNDF0TDROTFBsSjVTZkhWVFJRNVJUa2Zhck0yTVdfVG9rZW46Qm5uU2JHQm12b0s0eTB4SENyYWM0alFjbnpkXzE3NDg3OTM4MzU6MTc0ODc5NzQzNV9WNA" alt="img"></p><p>最后，在<code>application.yaml</code>中修改jdbc参数为你自己的数据库参数：</p><div class="language-YAML line-numbers-mode" data-highlighter="prismjs" data-ext="YAML" data-title="YAML"><pre class="language-YAML"><code><span class="line">spring:</span> <span class="line"> datasource:</span> <span class="line"> url: jdbc:mysql://127.0.0.1:3306/mp?useUnicode=true&characterEncoding=UTF-8&autoReconnect=true&serverTimezone=Asia/Shanghai</span> <span class="line"> driver-class-name: com.mysql.cj.jdbc.Driver</span> <span class="line"> username: root</span> <span class="line"> password: MySQL123</span> <span class="line">logging:</span> <span class="line"> level:</span> <span class="line"> com.itheima: debug</span> <span class="line"> pattern:</span> <span class="line"> dateformat: HH:mm:ss</span> <span class="line"></span></code></pre><div class="line-numbers" aria-hidden="true" style="counter-reset:line-number 0;"><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div></div></div><h2 id="_1-2-快速开始" tabindex="-1"><a class="header-anchor" href="#_1-2-快速开始"><span><strong>1.2.快速开始</strong></span></a></h2><p>比如我们要实现User表的CRUD，只需要下面几步：</p><ul><li>引入MybatisPlus依赖</li><li>定义Mapper</li></ul><h3 id="_1-2-1引入依赖" tabindex="-1"><a class="header-anchor" href="#_1-2-1引入依赖"><span><strong>1.2.1引入依赖</strong></span></a></h3><p>MybatisPlus提供了starter，实现了自动Mybatis以及MybatisPlus的自动装配功能，坐标如下：</p><div class="language-XML line-numbers-mode" data-highlighter="prismjs" data-ext="XML" data-title="XML"><pre class="language-XML"><code><span class="line"><dependency></span> <span class="line"> <groupId>com.baomidou</groupId></span> <span class="line"> <artifactId>mybatis-plus-boot-starter</artifactId></span> <span class="line"> <version>3.5.3.1</version></span> <span class="line"></dependency></span> <span class="line"></span></code></pre><div class="line-numbers" aria-hidden="true" style="counter-reset:line-number 0;"><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div></div></div><p>由于这个starter包含对mybatis的自动装配，因此完全可以替换掉Mybatis的starter。最终，项目的依赖如下：</p><div class="language-XML line-numbers-mode" data-highlighter="prismjs" data-ext="XML" data-title="XML"><pre class="language-XML"><code><span class="line"><dependencies></span> <span class="line"> <dependency></span> <span class="line"> <groupId>com.baomidou</groupId></span> <span class="line"> <artifactId>mybatis-plus-boot-starter</artifactId></span> <span class="line"> <version>3.5.3.1</version></span> <span class="line"> </dependency></span> <span class="line"> <dependency></span> <span class="line"> <groupId>com.mysql</groupId></span> <span class="line"> <artifactId>mysql-connector-j</artifactId></span> <span class="line"> <scope>runtime</scope></span> <span class="line"> </dependency></span> <span class="line"> <dependency></span> <span class="line"> <groupId>org.projectlombok</groupId></span> <span class="line"> <artifactId>lombok</artifactId></span> <span class="line"> <optional>true</optional></span> <span class="line"> </dependency></span> <span class="line"> <dependency></span> <span class="line"> <groupId>org.springframework.boot</groupId></span> <span class="line"> <artifactId>spring-boot-starter-test</artifactId></span> <span class="line"> <scope>test</scope></span> <span class="line"> </dependency></span> <span class="line"></dependencies></span> <span class="line"></span></code></pre><div class="line-numbers" aria-hidden="true" style="counter-reset:line-number 0;"><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div></div></div><h3 id="_1-2-2-定义mapper" tabindex="-1"><a class="header-anchor" href="#_1-2-2-定义mapper"><span><strong>1.2.2.定义Mapper</strong></span></a></h3><p>为了简化单表CRUD，MybatisPlus提供了一个基础的<code>BaseMapper</code>接口，其中已经实现了单表的CRUD：</p><p><img src="https://b11et3un53m.feishu.cn/space/api/box/stream/download/asynccode/?code=MTA4ODM5ODJjNDk0YTQzODhjMGM2ZDg0Mjc1ZDQ1MTlfMFkzdVN2dUdNVTFXUWFOQktwcTJrUEVlejhkOFEwakRfVG9rZW46S0ZZdmJYdzdmb1BmM0x4dzVDamNkbTdvbnRiXzE3NDg3OTM4MzU6MTc0ODc5NzQzNV9WNA" alt="img"></p><p>因此我们自定义的Mapper只要实现了这个<code>BaseMapper</code>，就无需自己实现单表CRUD了。修改mp-demo中的<code>com.itheima.mp.mapper</code>包下的<code>UserMapper</code>接口，让其继承<code>BaseMapper</code>：</p><p><img src="https://b11et3un53m.feishu.cn/space/api/box/stream/download/asynccode/?code=M2FjYjBiOTNhMzczODBiMDhmOWM1YWI2MzlmNDYwYjNfRnN5RWxmb1NVVTVBc0ZMREVvZjh4UmpJTUxTT1ZaSXFfVG9rZW46QzJDNGJOQ29yb25tMVB4aUQwS2NGNjdNbmxjXzE3NDg3OTM4MzU6MTc0ODc5NzQzNV9WNA" alt="img"></p><p>代码如下：</p><div class="language-Java line-numbers-mode" data-highlighter="prismjs" data-ext="Java" data-title="Java"><pre class="language-Java"><code><span class="line">package com.itheima.mp.mapper;</span> <span class="line"></span> <span class="line">import com.baomidou.mybatisplus.core.mapper.BaseMapper;</span> <span class="line">import com.itheima.mp.domain.po.User;</span> <span class="line"></span> <span class="line">public interface UserMapper extends BaseMapper<User> {</span> <span class="line">}</span> <span class="line"></span></code></pre><div class="line-numbers" aria-hidden="true" style="counter-reset:line-number 0;"><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div></div></div><h3 id="_1-2-3-测试" tabindex="-1"><a class="header-anchor" href="#_1-2-3-测试"><span><strong>1.2.3.测试</strong></span></a></h3><p>新建一个测试类，编写几个单元测试，测试基本的CRUD功能：</p><div class="language-Java line-numbers-mode" data-highlighter="prismjs" data-ext="Java" data-title="Java"><pre class="language-Java"><code><span class="line">package com.itheima.mp.mapper;</span> <span class="line"></span> <span class="line">import com.itheima.mp.domain.po.User;</span> <span class="line">import org.junit.jupiter.api.Test;</span> <span class="line">import org.springframework.beans.factory.annotation.Autowired;</span> <span class="line">import org.springframework.boot.test.context.SpringBootTest;</span> <span class="line"></span> <span class="line">import java.time.LocalDateTime;</span> <span class="line">import java.util.List;</span> <span class="line"></span> <span class="line">@SpringBootTest</span> <span class="line">class UserMapperTest {</span> <span class="line"></span> <span class="line"> @Autowired</span> <span class="line"> private UserMapper userMapper;</span> <span class="line"></span> <span class="line"> @Test</span> <span class="line"> void testInsert() {</span> <span class="line"> User user = new User();</span> <span class="line"> user.setId(5L);</span> <span class="line"> user.setUsername("Lucy");</span> <span class="line"> user.setPassword("123");</span> <span class="line"> user.setPhone("18688990011");</span> <span class="line"> user.setBalance(200);</span> <span class="line"> user.setInfo("{\"age\": 24, \"intro\": \"英文老师\", \"gender\": \"female\"}");</span> <span class="line"> user.setCreateTime(LocalDateTime.now());</span> <span class="line"> user.setUpdateTime(LocalDateTime.now());</span> <span class="line"> userMapper.insert(user);</span> <span class="line"> }</span> <span class="line"></span> <span class="line"> @Test</span> <span class="line"> void testSelectById() {</span> <span class="line"> User user = userMapper.selectById(5L);</span> <span class="line"> System.out.println("user = " + user);</span> <span class="line"> }</span> <span class="line"></span> <span class="line"> @Test</span> <span class="line"> void testSelectByIds() {</span> <span class="line"> List<User> users = userMapper.selectBatchIds(List.of(1L, 2L, 3L, 4L, 5L));</span> <span class="line"> users.forEach(System.out::println);</span> <span class="line"> }</span> <span class="line"></span> <span class="line"> @Test</span> <span class="line"> void testUpdateById() {</span> <span class="line"> User user = new User();</span> <span class="line"> user.setId(5L);</span> <span class="line"> user.setBalance(20000);</span> <span class="line"> userMapper.updateById(user);</span> <span class="line"> }</span> <span class="line"></span> <span class="line"> @Test</span> <span class="line"> void testDelete() {</span> <span class="line"> userMapper.deleteById(5L);</span> <span class="line"> }</span> <span class="line">}</span> <span class="line"></span></code></pre><div class="line-numbers" aria-hidden="true" style="counter-reset:line-number 0;"><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div></div></div><p>可以看到，在运行过程中打印出的SQL日志，非常标准：</p><div class="language-SQL line-numbers-mode" data-highlighter="prismjs" data-ext="SQL" data-title="SQL"><pre class="language-SQL"><code><span class="line">11:05:01 INFO 15524 --- [ main] com.zaxxer.hikari.HikariDataSource : HikariPool-1 - Starting...</span> <span class="line">11:05:02 INFO 15524 --- [ main] com.zaxxer.hikari.HikariDataSource : HikariPool-1 - Start completed.</span> <span class="line">11:05:02 DEBUG 15524 --- [ main] c.i.mp.mapper.UserMapper.selectById : ==> Preparing: SELECT id,username,password,phone,info,status,balance,create_time,update_time FROM user WHERE id=?</span> <span class="line">11:05:02 DEBUG 15524 --- [ main] c.i.mp.mapper.UserMapper.selectById : ==> Parameters: 5(Long)</span> <span class="line">11:05:02 DEBUG 15524 --- [ main] c.i.mp.mapper.UserMapper.selectById : <== Total: 1</span> <span class="line">user = User(id=5, username=Lucy, password=123, phone=18688990011, info={"age": 21}, status=1, balance=20000, createTime=Fri Jun 30 11:02:30 CST 2023, updateTime=Fri Jun 30 11:02:30 CST 2023)</span> <span class="line"></span></code></pre><div class="line-numbers" aria-hidden="true" style="counter-reset:line-number 0;"><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div></div></div><p>只需要继承BaseMapper就能省去所有的单表CRUD，是不是非常简单！</p><h2 id="_1-3-常见注解" tabindex="-1"><a class="header-anchor" href="#_1-3-常见注解"><span>**1.3.**<strong>常见注解</strong></span></a></h2><p>在刚刚的入门案例中，我们仅仅引入了依赖，继承了BaseMapper就能使用MybatisPlus，非常简单。但是问题来了： MybatisPlus如何知道我们要查询的是哪张表？表中有哪些字段呢？</p><p>大家回忆一下，UserMapper在继承BaseMapper的时候指定了一个泛型：</p><p><img src="https://b11et3un53m.feishu.cn/space/api/box/stream/download/asynccode/?code=ZmJmODU1ZDY4MzhiMzc0ZTk4YWI0MGY2ODQ0MDhiM2VfTEtMbnJjNUUzSFhXeTB1YmgycHNsQ3BnODROczZIUXZfVG9rZW46U1N6b2JzS1cxbzUySnh4WlRaamMyZU45bmhlXzE3NDg3OTM4MzU6MTc0ODc5NzQzNV9WNA" alt="img"></p><p>泛型中的User就是与数据库对应的PO.</p><p>MybatisPlus就是根据PO实体的信息来推断出表的信息，从而生成SQL的。默认情况下：</p><ul><li>MybatisPlus会把PO实体的类名驼峰转下划线作为表名</li><li>MybatisPlus会把PO实体的所有变量名驼峰转下划线作为表的字段名，并根据变量类型推断字段类型</li><li>MybatisPlus会把名为id的字段作为主键</li></ul><p>但很多情况下，默认的实现与实际场景不符，因此MybatisPlus提供了一些注解便于我们声明表信息。</p><h3 id="_1-3-1-tablename" tabindex="-1"><a class="header-anchor" href="#_1-3-1-tablename"><span>**1.3.1.@**<strong>TableName</strong></span></a></h3><p>说明：</p><ul><li>描述：表名注解，标识实体类对应的表</li><li>使用位置：实体类</li></ul><p>示例：</p><div class="language-Java line-numbers-mode" data-highlighter="prismjs" data-ext="Java" data-title="Java"><pre class="language-Java"><code><span class="line">@TableName("user")</span> <span class="line">public class User {</span> <span class="line"> private Long id;</span> <span class="line"> private String name;</span> <span class="line">}</span> <span class="line"></span></code></pre><div class="line-numbers" aria-hidden="true" style="counter-reset:line-number 0;"><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div></div></div><p>TableName注解除了指定表名以外，还可以指定很多其它属性：</p><table><thead><tr><th><strong>属性</strong></th><th><strong>类型</strong></th><th><strong>必须指定</strong></th><th><strong>默认值</strong></th><th><strong>描述</strong></th></tr></thead><tbody><tr><td>value</td><td>String</td><td>否</td><td>""</td><td>表名</td></tr><tr><td>schema</td><td>String</td><td>否</td><td>""</td><td>schema</td></tr><tr><td>keepGlobalPrefix</td><td>boolean</td><td>否</td><td>false</td><td>是否保持使用全局的 tablePrefix 的值（当全局 tablePrefix 生效时）</td></tr><tr><td>resultMap</td><td>String</td><td>否</td><td>""</td><td>xml 中 resultMap 的 id（用于满足特定类型的实体类对象绑定）</td></tr><tr><td>autoResultMap</td><td>boolean</td><td>否</td><td>false</td><td>是否自动构建 resultMap 并使用（如果设置 resultMap 则不会进行 resultMap 的自动构建与注入）</td></tr><tr><td>excludeProperty</td><td>String[]</td><td>否</td><td>{}</td><td>需要排除的属性名 @since 3.3.1</td></tr></tbody></table><h3 id="_1-3-2-tableid" tabindex="-1"><a class="header-anchor" href="#_1-3-2-tableid"><span><strong>1.3.2.@TableId</strong></span></a></h3><p>说明：</p><ul><li>描述：主键注解，标识实体类中的主键字段</li><li>使用位置：实体类的主键字段</li></ul><p>示例：</p><div class="language-Java line-numbers-mode" data-highlighter="prismjs" data-ext="Java" data-title="Java"><pre class="language-Java"><code><span class="line">@TableName("user")</span> <span class="line">public class User {</span> <span class="line"> @TableId</span> <span class="line"> private Long id;</span> <span class="line"> private String name;</span> <span class="line">}</span> <span class="line"></span></code></pre><div class="line-numbers" aria-hidden="true" style="counter-reset:line-number 0;"><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div></div></div><p><code>TableId</code>注解支持两个属性：</p><table><thead><tr><th style="text-align:left;"><strong>属性</strong></th><th style="text-align:left;"><strong>类型</strong></th><th style="text-align:left;"><strong>必须指定</strong></th><th style="text-align:left;"><strong>默认值</strong></th><th style="text-align:left;"><strong>描述</strong></th></tr></thead><tbody><tr><td style="text-align:left;">value</td><td style="text-align:left;">String</td><td style="text-align:left;">否</td><td style="text-align:left;">""</td><td style="text-align:left;">表名</td></tr><tr><td style="text-align:left;">type</td><td style="text-align:left;">Enum</td><td style="text-align:left;">否</td><td style="text-align:left;">IdType.NONE</td><td style="text-align:left;">指定主键类型</td></tr></tbody></table><p><code>IdType</code>支持的类型有：</p><table><thead><tr><th style="text-align:left;"><strong>值</strong></th><th style="text-align:left;"><strong>描述</strong></th></tr></thead><tbody><tr><td style="text-align:left;">AUTO</td><td style="text-align:left;">数据库 ID 自增</td></tr><tr><td style="text-align:left;">NONE</td><td style="text-align:left;">无状态，该类型为未设置主键类型（注解里等于跟随全局，全局里约等于 INPUT）</td></tr><tr><td style="text-align:left;">INPUT</td><td style="text-align:left;">insert 前自行 set 主键值</td></tr><tr><td style="text-align:left;">ASSIGN_ID</td><td style="text-align:left;">分配 ID(主键类型为 Number(Long 和 Integer)或 String)(since 3.3.0),使用接口IdentifierGenerator的方法nextId(默认实现类为DefaultIdentifierGenerator雪花算法)</td></tr><tr><td style="text-align:left;">ASSIGN_UUID</td><td style="text-align:left;">分配 UUID,主键类型为 String(since 3.3.0),使用接口IdentifierGenerator的方法nextUUID(默认 default 方法)</td></tr><tr><td style="text-align:left;">ID_WORKER</td><td style="text-align:left;">分布式全局唯一 ID 长整型类型(please use ASSIGN_ID)</td></tr><tr><td style="text-align:left;">UUID</td><td style="text-align:left;">32 位 UUID 字符串(please use ASSIGN_UUID)</td></tr><tr><td style="text-align:left;">ID_WORKER_STR</td><td style="text-align:left;">分布式全局唯一 ID 字符串类型(please use ASSIGN_ID)</td></tr></tbody></table><p>这里比较常见的有三种：</p><ul><li><code>AUTO</code>：利用数据库的id自增长</li><li><code>INPUT</code>：手动生成id</li><li><code>ASSIGN_ID</code>：雪花算法生成<code>Long</code>类型的全局唯一id，这是默认的ID策略</li></ul><h3 id="_1-3-3-tablefield" tabindex="-1"><a class="header-anchor" href="#_1-3-3-tablefield"><span><strong>1.3.3.@TableField</strong></span></a></h3><p>说明：</p><blockquote><p>描述：普通字段注解</p></blockquote><p>示例：</p><div class="language-Java line-numbers-mode" data-highlighter="prismjs" data-ext="Java" data-title="Java"><pre class="language-Java"><code><span class="line">@TableName("user")</span> <span class="line">public class User {</span> <span class="line"> @TableId</span> <span class="line"> private Long id;</span> <span class="line"> private String name;</span> <span class="line"> private Integer age;</span> <span class="line"> @TableField(is_married")</span> <span class="line"> private Boolean isMarried;</span> <span class="line"> @TableField("`concat`")</span> <span class="line"> private String concat;</span> <span class="line">}</span> <span class="line"></span></code></pre><div class="line-numbers" aria-hidden="true" style="counter-reset:line-number 0;"><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div></div></div><p>一般情况下我们并不需要给字段添加<code>@TableField</code>注解，一些特殊情况除外：</p><ul><li>成员变量名与数据库字段名不一致</li><li>成员变量是以<code>isXXX</code>命名，按照<code>JavaBean</code>的规范，<code>MybatisPlus</code>识别字段时会把<code>is</code>去除，这就导致与数据库不符。</li><li>成员变量名与数据库一致，但是与数据库的关键字冲突。使用<code>@TableField</code>注解给字段名添加转义字符：````</li></ul><p>支持的其它属性如下：</p><table><thead><tr><th><strong>属性</strong></th><th><strong>类型</strong></th><th><strong>必填</strong></th><th><strong>默认值</strong></th><th><strong>描述</strong></th></tr></thead><tbody><tr><td>value</td><td>String</td><td>否</td><td>""</td><td>数据库字段名</td></tr><tr><td>exist</td><td>boolean</td><td>否</td><td>true</td><td>是否为数据库表字段</td></tr><tr><td>condition</td><td>String</td><td>否</td><td>""</td><td>字段 where 实体查询比较条件，有值设置则按设置的值为准，没有则为默认全局的 %s=#{%s}，<a href="https://github.com/baomidou/mybatis-plus/blob/3.0/mybatis-plus-annotation/src/main/java/com/baomidou/mybatisplus/annotation/SqlCondition.java" target="_blank" rel="noopener noreferrer">参考(opens new window)</a></td></tr><tr><td>update</td><td>String</td><td>否</td><td>""</td><td>字段 update set 部分注入，例如：当在version字段上注解update="%s+1" 表示更新时会 set version=version+1 （该属性优先级高于 el 属性）</td></tr><tr><td>insertStrategy</td><td>Enum</td><td>否</td><td>FieldStrategy.DEFAULT</td><td>举例：NOT_NULL insert into table_a() values ()</td></tr><tr><td>updateStrategy</td><td>Enum</td><td>否</td><td>FieldStrategy.DEFAULT</td><td>举例：IGNORED update table_a set column=#{columnProperty}</td></tr><tr><td>whereStrategy</td><td>Enum</td><td>否</td><td>FieldStrategy.DEFAULT</td><td>举例：NOT_EMPTY where </td></tr><tr><td>fill</td><td>Enum</td><td>否</td><td>FieldFill.DEFAULT</td><td>字段自动填充策略</td></tr><tr><td>select</td><td>boolean</td><td>否</td><td>true</td><td>是否进行 select 查询</td></tr><tr><td>keepGlobalFormat</td><td>boolean</td><td>否</td><td>false</td><td>是否保持使用全局的 format 进行处理</td></tr><tr><td>jdbcType</td><td>JdbcType</td><td>否</td><td>JdbcType.UNDEFINED</td><td>JDBC 类型 (该默认值不代表会按照该值生效)</td></tr><tr><td>typeHandler</td><td>TypeHander</td><td>否</td><td></td><td>类型处理器 (该默认值不代表会按照该值生效)</td></tr><tr><td>numericScale</td><td>String</td><td>否</td><td>""</td><td>指定小数点后保留的位数</td></tr></tbody></table><h2 id="_1-4-常见配置" tabindex="-1"><a class="header-anchor" href="#_1-4-常见配置"><span><strong>1.4.常见配置</strong></span></a></h2><p>MybatisPlus也支持基于yaml文件的自定义配置，详见官方文档：</p><p>https://baomidou.com/reference/</p><p>大多数的配置都有默认值，因此我们都无需配置。但还有一些是没有默认值的，例如:</p><ul><li>实体类的别名扫描包</li><li>全局id类型</li></ul><div class="language-YAML line-numbers-mode" data-highlighter="prismjs" data-ext="YAML" data-title="YAML"><pre class="language-YAML"><code><span class="line">mybatis-plus:</span> <span class="line"> type-aliases-package: com.itheima.mp.domain.po</span> <span class="line"> global-config:</span> <span class="line"> db-config:</span> <span class="line"> id-type: auto # 全局id类型为自增长</span> <span class="line"></span></code></pre><div class="line-numbers" aria-hidden="true" style="counter-reset:line-number 0;"><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div></div></div><p>需要注意的是，MyBatisPlus也支持手写SQL的，而mapper文件的读取地址可以自己配置：</p><div class="language-YAML line-numbers-mode" data-highlighter="prismjs" data-ext="YAML" data-title="YAML"><pre class="language-YAML"><code><span class="line">mybatis-plus:</span> <span class="line"> mapper-locations: "classpath*:/mapper/**/*.xml" # Mapper.xml文件地址，当前这个是默认值。</span> <span class="line"></span></code></pre><div class="line-numbers" aria-hidden="true" style="counter-reset:line-number 0;"><div class="line-number"></div><div class="line-number"></div></div></div><p>可以看到默认值是<code>classpath*:/mapper/**/*.xml</code>，也就是说我们只要把mapper.xml文件放置这个目录下就一定会被加载。</p><p>例如，我们新建一个<code>UserMapper.xml</code>文件：</p><p><img src="https://b11et3un53m.feishu.cn/space/api/box/stream/download/asynccode/?code=NDFhZTZlMzdlZjQ3NjE3OGFjNGEwMWM0MzhkMmNkOWVfbDZNVVZSYXdNM3FsWjl4Sjd0M2kyaUU0c1ZOUVhvT3hfVG9rZW46RnhoNGJBQVZLb3Rpcmd4a24xNWNVMUhXbkRoXzE3NDg3OTM4MzU6MTc0ODc5NzQzNV9WNA" alt="img"></p><p>然后在其中定义一个方法：</p><div class="language-XML line-numbers-mode" data-highlighter="prismjs" data-ext="XML" data-title="XML"><pre class="language-XML"><code><span class="line"><?xml version="1.0" encoding="UTF-8"?></span> <span class="line"><!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN" "http://mybatis.org/dtd/mybatis-3-mapper.dtd"></span> <span class="line"><mapper namespace="com.itheima.mp.mapper.UserMapper"></span> <span class="line"></span> <span class="line"> <select id="queryById" resultType="User"></span> <span class="line"> SELECT * FROM user WHERE id = #{id}</span> <span class="line"> </select></span> <span class="line"></mapper></span> <span class="line"></span></code></pre><div class="line-numbers" aria-hidden="true" style="counter-reset:line-number 0