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java每日精进 5.20【MyBatis 联表分页查询】

news 2025/5/24 15:54:05

1. MyBatis XML 实现分页查询

1.1 实现方式

MyBatis XML 是一种传统的 MyBatis 使用方式，通过在 XML 文件中编写 SQL 语句，并结合 Mapper 接口和 Service 层实现分页查询。分页需要手动编写两条 SQL 语句：一条查询分页数据列表，另一条查询总记录数。分页参数（如页码和每页大小）通过 LIMIT 语句手动实现。

1.2 代码解析

以下是文档中提供的 MyBatis XML 分页查询代码的解析：

1.2.1 xml代码

// 获取所有用户（分页，支持用户名模糊查询）@GetMapping("/xmluserpage")public IPage<User> getUsersByPage(@RequestParam(defaultValue = "1") int page,@RequestParam(defaultValue = "10") int size,@RequestParam(required = false) String username) {return userService.getUserPage(page, size, username);}
@Overridepublic IPage<User> getUserPage(int page, int size, String username) {Page<User> userPage = new Page<>(page, size);return userMapper.selectPageCustom(userPage, username);}
// 自定义分页查询（单表）IPage<User> selectPageCustom(Page<User> page, @Param("username") String username);

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN" "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
<mapper namespace="com.home.mapper.UserMapper"><!-- 自定义分页查询 --><select id="selectPageCustom" resultType="com.home.pojo.User">SELECT id, username, password, email, create_time, update_timeFROM user<where><if test="username != null and username != ''">AND username LIKE CONCAT('%', #{username}, '%')</if></where></select></mapper>

2. MyBatis XML 联表查询

2.1背景代码

<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd"><modelVersion>4.0.0</modelVersion><groupId>org.example</groupId><artifactId>CRUDSystem</artifactId><version>1.0-SNAPSHOT</version><packaging>jar</packaging> <!-- 建议改为jar，Spring Boot默认打包为可执行jar --><name>CRUDSystem</name><url>http://www.example.com</url><properties><project.build.sourceEncoding>UTF-8</project.build.sourceEncoding><maven.compiler.source>17</maven.compiler.source><maven.compiler.target>17</maven.compiler.target><spring-boot.version>2.7.18</spring-boot.version><mybatis-plus.version>3.5.3.1</mybatis-plus.version><mybatis-plus-join.version>1.4.10</mybatis-plus-join.version></properties><dependencies><!-- MyBatis Plus --><dependency><groupId>com.baomidou</groupId><artifactId>mybatis-plus-boot-starter</artifactId><version>${mybatis-plus.version}</version></dependency><!-- MyBatis Plus Join --><dependency><groupId>com.github.yulichang</groupId><artifactId>mybatis-plus-join-boot-starter</artifactId><version>${mybatis-plus-join.version}</version></dependency><dependency><groupId>com.baomidou</groupId><artifactId>mybatis-plus-extension</artifactId><version>${mybatis-plus.version}</version></dependency><!-- MySQL 驱动 --><dependency><groupId>mysql</groupId><artifactId>mysql-connector-java</artifactId><version>8.0.33</version></dependency><!-- Spring Boot 核心 --><dependency><groupId>org.springframework.boot</groupId><artifactId>spring-boot-starter</artifactId><version>${spring-boot.version}</version></dependency><dependency><groupId>org.springframework.boot</groupId><artifactId>spring-boot-starter-web</artifactId><version>${spring-boot.version}</version></dependency><!-- Lombok --><dependency><groupId>org.projectlombok</groupId><artifactId>lombok</artifactId><version>1.18.28</version></dependency><!-- 测试依赖 --><dependency><groupId>org.springframework.boot</groupId><artifactId>spring-boot-starter-test</artifactId><version>${spring-boot.version}</version><scope>test</scope></dependency></dependencies><build><finalName>CRUDSystem</finalName><plugins><!-- Spring Boot 打包插件 --><plugin><groupId>org.springframework.boot</groupId><artifactId>spring-boot-maven-plugin</artifactId><version>${spring-boot.version}</version><configuration><excludes><exclude><groupId>org.projectlombok</groupId><artifactId>lombok</artifactId></exclude></excludes></configuration></plugin><!-- 编译插件 --><plugin><groupId>org.apache.maven.plugins</groupId><artifactId>maven-compiler-plugin</artifactId><version>3.8.1</version><configuration><source>17</source><target>17</target><release>17</release></configuration></plugin></plugins></build>
</project>
@Data
@TableName("user")
public class User {@TableId(type = IdType.AUTO)private Long id;private String username;private String password;private String email;@TableField(fill = FieldFill.INSERT)private LocalDateTime createTime;@TableField(fill = FieldFill.INSERT_UPDATE)private LocalDateTime updateTime;
}
@Data
@TableName("`order`")
public class Order {@TableId(type = IdType.AUTO)private Long id;private Long userId;private Long productId;private Integer quantity;private BigDecimal totalPrice;private Integer status;@TableField(fill = FieldFill.INSERT)private LocalDateTime createTime;@TableField(fill = FieldFill.INSERT_UPDATE)private LocalDateTime updateTime;
}
//字段平铺
@Data
public class UserOrderDetailDO extends User {private Long orderId;private BigDecimal totalPrice;private Integer orderStatus;
}
//字段内嵌
@Data
public class UserOrderDetail2DO extends User {private Order order;
}

2.2字段平铺

// 字段平铺：获取用户订单详情（分页，订单状态和用户名过滤）@GetMapping("/orders")public IPage<UserOrderDetailDO> getUserOrders(@RequestParam(defaultValue = "1") int page,@RequestParam(defaultValue = "10") int size,@RequestParam Integer status,@RequestParam(required = false) String username) {return userService.getUserOrderPage(page, size, status, username);}@Overridepublic IPage<UserOrderDetailDO> getUserOrderPage(int page, int size, Integer status, String username) {Page<UserOrderDetailDO> userOrderPage = new Page<>(page, size);return userMapper.selectListByStatusAndUsername(userOrderPage, status, username);}
// 字段平铺：联表查询用户和订单（状态为已支付，用户名模糊匹配）default IPage<UserOrderDetailDO> selectListByStatusAndUsername(Page<UserOrderDetailDO> page,@Param("status") Integer status,@Param("username") String username) {return selectJoinPage(page, UserOrderDetailDO.class, new MPJLambdaWrapper<User>() // 改为 selectJoinPage.selectAll(User.class).selectAs(Order::getId, UserOrderDetailDO::getOrderId).selectAs(Order::getTotalPrice, UserOrderDetailDO::getTotalPrice).selectAs(Order::getStatus, UserOrderDetailDO::getOrderStatus).eq(Order::getStatus, status).leftJoin(Order.class, Order::getUserId, User::getId).like(username != null, User::getUsername, username));}

等价于以下SQL

SELECT 
    u.*,
    o.id AS orderId,
    o.total_price AS totalPrice,
    o.status AS orderStatus
FROM 
    user u
LEFT JOIN 
    `order` o ON u.id = o.user_id  -- 注意这里应该是 user_id 而不是 o.id
WHERE 
    o.status = 1 
    AND u.username LIKE '%username%'

查询结果：

{"records": [{"id": 1,"username": "user1","password": "password123","email": "user1@example.com","createTime": "2025-05-20T10:15:33","updateTime": "2025-05-20T10:15:33","orderId": 1,"totalPrice": 999.99,"orderStatus": 1}],"total": 2,"size": 1,"current": 1,"orders": [],"optimizeCountSql": true,"searchCount": true,"maxLimit": null,"countId": null,"pages": 2
}

2.3字段嵌入

// 字段内嵌：获取用户订单详情（分页，订单状态和用户名过滤）@GetMapping("/orders2")public IPage<UserOrderDetail2DO> getUserOrders2(@RequestParam(defaultValue = "1") int page,@RequestParam(defaultValue = "10") int size,@RequestParam Integer status,@RequestParam(required = false) String username) {return userService.getUserOrderPage2(page, size, status, username);}
@Overridepublic IPage<UserOrderDetail2DO> getUserOrderPage2(int page, int size, Integer status, String username) {Page<UserOrderDetail2DO> userOrderPage = new Page<>(page, size);return userMapper.selectList2ByStatusAndUsername(userOrderPage, status, username);}
// 字段内嵌：联表查询用户和订单（状态为已支付，用户名模糊匹配）default IPage<UserOrderDetail2DO> selectList2ByStatusAndUsername(Page<UserOrderDetail2DO> page,@Param("status") Integer status,@Param("username") String username) {return selectJoinPage(page, UserOrderDetail2DO.class, new MPJLambdaWrapper<User>() // 改为 selectJoinPage.selectAll(User.class).selectAssociation(Order.class, UserOrderDetail2DO::getOrder).eq(Order::getStatus, status).leftJoin(Order.class, Order::getUserId, User::getId).like(username != null, User::getUsername, username));}

等价SQL：

SELECT 
    u.*, 
    o.*
FROM 
    t_user u
LEFT JOIN 
    t_order o ON o.user_id = u.id
WHERE 
    o.status = #{status}
    AND (#{username} IS NULL OR u.username LIKE CONCAT('%', #{username}, '%'))
LIMIT #{page.size} OFFSET #{page.offset}

返回值为：

{"records": [{"id": 1,"username": "user1","password": "password123","email": "user1@example.com","createTime": "2025-05-20T10:15:33","updateTime": "2025-05-20T10:15:33","order": {"id": 1,"userId": 1,"productId": 1,"quantity": 1,"totalPrice": 999.99,"status": 1,"createTime": "2025-05-20T10:16:00","updateTime": "2025-05-20T10:16:00"}}],"total": 2,"size": 1,"current": 1,"orders": [],"optimizeCountSql": true,"searchCount": true,"maxLimit": null,"countId": null,"pages": 2
}

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