YinShunyu
2 weeks ago
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BIN尹顺宇学习笔记/尹顺宇11.08作业/尹顺宇11.08学习总结.docx
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379尹顺宇学习笔记/尹顺宇11.08作业/尹顺宇11.08学习笔记.md
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BIN尹顺宇学习笔记/尹顺宇11.08作业/尹顺宇11.08学习笔记.pdf
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BIN尹顺宇学习笔记/尹顺宇11.08作业/尹顺宇11.08股票知识学习.docx
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# Mybatis初步复习 |
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## 1.SpringBoot整合Mybatis |
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## 1.1第一步添加依赖 |
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``` |
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<!-- mybatis启动器--> |
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<dependency> |
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<groupId>org.mybatis.spring.boot</groupId> |
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<artifactId>mybatis-spring-boot-starter</artifactId> |
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<version>3.0.5</version> |
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</dependency> |
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``` |
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### 1.2进行配置 |
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``` |
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#配置Mybatis |
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mybatis: |
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configuration: |
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#在映射为java对象，将表中的下划线命名自动转换成驼峰式命名 |
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map-underscore-to-camel-case: true |
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#日志前缀 可选 |
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log-prefix: mybatis. |
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#日志实现类 可选 |
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log-impl: org.apache.ibatis.logging.commons.JakartaCommonsLoggingImpl |
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#动态sql文件存储位置 |
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mapper-locations: classpath:/mapper/**/*.xml |
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#配置日志显示sql |
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logging: |
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level: |
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#指定日志前缀 |
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mybatis: debug |
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``` |
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### 1.3 在Dao层编写的mapper接口，添加@Mapper注解 |
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### 1.4 编写动态sql文件（xx.xml文件） |
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### 1.5 安装mybatisx插件 |
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 |
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安装之后在mapper和动态SQL文件对应代码左边有一个小鸟图标，方便直接跳转 |
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## 2.自动映射 |
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当开启驼峰命名自动映射 |
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```yaml |
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mybatis: |
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configuration: |
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map-underscore-to-camel-case: true |
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``` |
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## 3.手动映射 |
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当自动映射无法满足需求时，可以使用 `<resultMap>` 进行精确的手动映射。 |
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```xml |
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<resultMap id="唯一标识" type="要映射的Java类型"> |
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<!-- 主键映射 --> |
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<id property="Java属性名" column="数据库列名"/> |
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<!-- 普通字段映射 --> |
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<result property="Java属性名" column="数据库列名"/> |
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<!-- 关联关系映射 --> |
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<association property="关联对象属性" javaType="关联对象类型"/> |
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<collection property="集合属性" ofType="集合元素类型"/> |
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</resultMap> |
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``` |
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举例： |
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### 3.1基础字段映射 |
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```java |
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实体类 |
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public class User { |
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private Long userId; // 与数据库字段名不同 |
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private String userName; // 需要手动映射 |
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private String email; |
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private Integer status; |
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private LocalDateTime createTime; |
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private LocalDateTime updateTime; |
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// 构造函数、getter、setter... |
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} |
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``` |
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```sql |
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数据库表结构： |
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CREATE TABLE t_user ( |
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id BIGINT PRIMARY KEY, |
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name VARCHAR(50), |
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email VARCHAR(100), |
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status TINYINT, |
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created_at DATETIME, |
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updated_at DATETIME |
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); |
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``` |
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```xml |
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<!-- 基础手动映射示例 --> |
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<resultMap id="BaseUserMap" type="User"> |
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<!-- 主键字段，使用 id 标签 --> |
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<id property="userId" column="id"/> |
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<!-- 普通字段，使用 result 标签 --> |
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<result property="userName" column="name"/> |
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<result property="email" column="email"/> |
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<result property="status" column="status"/> |
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<result property="createTime" column="created_at"/> |
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<result property="updateTime" column="updated_at"/> |
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</resultMap> |
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<!-- 使用 resultMap --> |
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<select id="selectUserById" resultMap="BaseUserMap"> |
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SELECT id, name, email, status, created_at, updated_at |
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FROM t_user |
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WHERE id = #{id} |
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</select> |
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``` |
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说明： |
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### 3.2一对一关联映射 |
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#### 3.2.1单次查询嵌套结果映射 |
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举例： |
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```java |
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实体类 |
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public class User { |
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private Long userId; |
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private String userName; |
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private UserProfile userProfile; // 一对一关联 |
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// getter/setter... |
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} |
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public class UserProfile { |
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private Long profileId; |
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private Long userId; |
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private String realName; |
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private Integer age; |
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private String address; |
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private String phone; |
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// getter/setter... |
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} |
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``` |
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```xml |
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手动映射配置： |
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<!-- 用户和用户详情的一对一映射 --> |
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<resultMap id="UserWithProfileMap" type="User"> |
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<id property="userId" column="id"/> |
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<result property="userName" column="name"/> |
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<!-- association: 一对一关联映射 --> |
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<association property="userProfile" javaType="UserProfile"> |
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<id property="profileId" column="profile_id"/> |
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<result property="userId" column="id"/> <!-- 注意：这里复用外层查询的id --> |
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<result property="realName" column="real_name"/> |
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<result property="age" column="age"/> |
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<result property="address" column="address"/> |
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<result property="phone" column="phone"/> |
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</association> |
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</resultMap> |
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<!-- 关联查询SQL --> |
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<select id="selectUserWithProfile" resultMap="UserWithProfileMap"> |
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SELECT |
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u.id, u.name, |
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up.id as profile_id, up.real_name, up.age, up.address, up.phone |
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FROM t_user u |
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LEFT JOIN t_user_profile up ON u.id = up.user_id |
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WHERE u.id = #{userId} |
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</select> |
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``` |
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#### 3.2.2 多次查询嵌套查询映射 |
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```xml |
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<!-- 主结果映射 --> |
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<resultMap id="UserWithProfileNestedMap" type="User"> |
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<id property="userId" column="id"/> |
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<result property="userName" column="name"/> |
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<!-- 嵌套查询：通过 select 属性引用另一个查询 --> |
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<association property="userProfile" column="id" |
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select="selectUserProfileByUserId"/> |
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</resultMap> |
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<!-- 主查询 --> |
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<select id="selectUserWithProfileNested" resultMap="UserWithProfileNestedMap"> |
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SELECT id, name |
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FROM t_user |
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WHERE id = #{userId} |
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</select> |
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<!-- 嵌套查询 --> |
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<select id="selectUserProfileByUserId" resultType="UserProfile"> |
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SELECT |
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id as profileId, |
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user_id as userId, |
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real_name as realName, |
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age, address, phone |
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FROM t_user_profile` |
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WHERE user_id = #{userId} |
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</select> |
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``` |
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### 3.3一对多集合映射 |
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```java |
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实体类： |
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public class User { |
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private Long userId; |
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private String userName; |
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private List<Order> orders; // 一对多关联 |
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// getter/setter... |
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} |
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public class Order { |
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private Long orderId; |
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private Long userId; |
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private String orderNumber; |
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private BigDecimal amount; |
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private LocalDateTime orderTime; |
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// getter/setter... |
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} |
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``` |
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```xml |
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<!-- 用户和订单的一对多映射 --> |
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<resultMap id="UserWithOrdersMap" type="User"> |
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<id property="userId" column="id"/> |
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<result property="userName" column="name"/> |
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<!-- collection: 一对多关联映射 --> |
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<collection property="orders" ofType="Order"> |
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<id property="orderId" column="order_id"/> |
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<result property="userId" column="id"/> <!-- 注意：这里复用外层查询的id --> |
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<result property="orderNumber" column="order_number"/> |
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<result property="amount" column="amount"/> |
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<result property="orderTime" column="order_time"/> |
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</collection> |
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</resultMap> |
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<!-- 关联查询SQL --> |
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<select id="selectUserWithOrders" resultMap="UserWithOrdersMap"> |
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SELECT |
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u.id, u.name, |
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o.id as order_id, o.order_number, o.amount, o.order_time |
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FROM t_user u |
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LEFT JOIN t_order o ON u.id = o.user_id |
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WHERE u.id = #{userId} |
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</select> |
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``` |
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### 3.4复杂的多层嵌套 |
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```java |
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public class User { |
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private Long userId; |
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private String userName; |
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private List<Order> orders; |
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} |
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public class Order { |
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private Long orderId; |
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private String orderNumber; |
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private List<OrderItem> orderItems; |
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} |
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public class OrderItem { |
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private Long itemId; |
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private Long productId; |
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private Integer quantity; |
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private Product product; // 关联商品 |
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} |
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public class Product { |
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private Long productId; |
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private String productName; |
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private BigDecimal price; |
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} |
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``` |
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```xml |
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<!-- 完整的多层嵌套映射 --> |
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<resultMap id="CompleteUserMap" type="User"> |
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<id property="userId" column="user_id"/> |
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<result property="userName" column="user_name"/> |
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<!-- 第一层嵌套：订单集合 --> |
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<collection property="orders" ofType="Order" resultMap="OrderWithItemsMap"/> |
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</resultMap> |
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<resultMap id="OrderWithItemsMap" type="Order"> |
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<id property="orderId" column="order_id"/> |
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<result property="orderNumber" column="order_number"/> |
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<!-- 第二层嵌套：订单项集合 --> |
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<collection property="orderItems" ofType="OrderItem" resultMap="OrderItemMap"/> |
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</resultMap> |
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<resultMap id="OrderItemMap" type="OrderItem"> |
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<id property="itemId" column="item_id"/> |
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<result property="quantity" column="quantity"/> |
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<!-- 第三层嵌套：商品信息 --> |
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<association property="product" javaType="Product"> |
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<id property="productId" column="product_id"/> |
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<result property="productName" column="product_name"/> |
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<result property="price" column="price"/> |
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</association> |
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</resultMap> |
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<!-- 复杂查询SQL --> |
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<select id="selectUserWithOrderDetails" resultMap="CompleteUserMap"> |
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SELECT |
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u.id as user_id, u.name as user_name, |
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o.id as order_id, o.order_number, |
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oi.id as item_id, oi.quantity, |
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p.id as product_id, p.name as product_name, p.price |
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FROM t_user u |
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LEFT JOIN t_order o ON u.id = o.user_id |
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LEFT JOIN t_order_item oi ON o.id = oi.order_id |
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LEFT JOIN t_product p ON oi.product_id = p.id |
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WHERE u.id = #{userId} |
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ORDER BY o.order_time DESC, oi.id |
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</select> |
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``` |
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### 3.5.注意 |
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1.可以 自动映射与手动映射结合 |
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```xml |
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<!-- 混合映射：autoMapping="true" 开启自动映射 --> |
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<resultMap id="HybridUserMap" type="User" autoMapping="true"> |
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<!-- 只手动映射名称不匹配的字段 --> |
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<id property="userId" column="id"/> |
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<result property="userName" column="name"/> |
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<result property="createTime" column="created_at"/> |
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<!-- 关联对象也可以使用自动映射 --> |
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<association property="userProfile" javaType="UserProfile" autoMapping="true"> |
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<id property="profileId" column="profile_id"/> |
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<!-- 只覆盖需要特殊处理的字段 --> |
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<result property="realName" column="real_name"/> |
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</association> |
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</resultMap> |
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``` |
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## |
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