使用MyBatis-Plus實現(xiàn)聯(lián)表查詢分頁的示例代碼

更新時間：2024年10月11日 11:19:19 作者：李少兄

本文主要講述了如何在SpringBoot項目中使用MyBatis-Plus的分頁插件,通過這個示例,可以學會如何利用MyBatis-Plus進行高效的分頁查詢,感興趣的可以了解一下

前言

在本文中，我們將詳細介紹如何使用 MyBatis-Plus 的分頁插件在 XML 文件中實現(xiàn)聯(lián)表查詢的分頁功能。

環(huán)境準備

項目環(huán)境

Java 版本: 1.8+
Spring Boot 版本: 2.x
MyBatis-Plus 版本: 3.x
數(shù)據(jù)庫: MySQL

添加依賴

確保你的項目中添加了 MyBatis-Plus 的相關(guān)依賴。如果你使用 Maven，可以在 pom.xml 文件中添加如下依賴：

<dependencies>
    <dependency>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-data-mybatis-plus</artifactId>
    </dependency>
    <dependency>
        <groupId>mysql</groupId>
        <artifactId>mysql-connector-java</artifactId>
        <scope>runtime</scope>
    </dependency>
    <!-- 其他依賴 -->
</dependencies>

配置數(shù)據(jù)庫連接

在 application.properties 或 application.yml 文件中配置數(shù)據(jù)庫連接信息：

spring.datasource.url=jdbc:mysql://localhost:3306/mydatabase?useUnicode=true&characterEncoding=utf8&serverTimezone=UTC
spring.datasource.username=root
spring.datasource.password=root
spring.datasource.driver-class-name=com.mysql.cj.jdbc.Driver

實體類定義

首先，定義幾個基本的實體類：

User.java

package com.microsun.integrated.framework.domain;

import lombok.AllArgsConstructor;
import lombok.Data;
import lombok.NoArgsConstructor;

@Data
@NoArgsConstructor
@AllArgsConstructor
public class User {
    private Long id;
    private String name;
    // Getters and Setters
}

UserRole.java

package com.microsun.integrated.framework.domain;

import lombok.AllArgsConstructor;
import lombok.Data;
import lombok.NoArgsConstructor;

@Data
@NoArgsConstructor
@AllArgsConstructor
public class UserRole {
    private Long userId;
    private Long roleId;
    // Getters and Setters
}

Role.java

package com.microsun.integrated.framework.domain;

import lombok.AllArgsConstructor;
import lombok.Data;
import lombok.NoArgsConstructor;

@Data
@NoArgsConstructor
@AllArgsConstructor
public class Role {
    private Long id;
    private String roleName;
    // Getters and Setters
}

RoleVo.java (用于展示的視圖對象)

package com.microsun.integrated.framework.domain;

import lombok.AllArgsConstructor;
import lombok.Data;
import lombok.NoArgsConstructor;

@Data
@NoArgsConstructor
@AllArgsConstructor
public class RoleVo {
    private Long userId;
    private String roleName;
    // Getters and Setters
}

分頁返回對象

為了封裝分頁返回的對象，我們定義了一個 PageVO 類：

PageVO.java

package com.microsun.integrated.framework.domain;

import io.swagger.v3.oas.annotations.media.Schema;
import lombok.AllArgsConstructor;
import lombok.Data;
import lombok.NoArgsConstructor;

import java.util.List;

@Data
@NoArgsConstructor
@AllArgsConstructor
@Schema(title = "分頁")
public class PageVO<T> {

    @Schema(title = "總數(shù)")
    private Long total;

    @Schema(title = "每頁顯示條數(shù)")
    private Long size;

    @Schema(title = "當前頁")
    private Long current;

    @Schema(title = "數(shù)據(jù)列表")
    private List<T> records;
}

請求參數(shù)封裝

接下來，我們創(chuàng)建一個 BO (Business Object) 對象來封裝請求參數(shù)：

UserRoleQueryBO.java

package com.microsun.integrated.framework.domain;

import io.swagger.v3.oas.annotations.media.Schema;
import lombok.AllArgsConstructor;
import lombok.Data;
import lombok.NoArgsConstructor;

/**
 * 用戶角色查詢 BO
 */
@Data
@NoArgsConstructor
@AllArgsConstructor
@Schema(title = "用戶角色查詢 BO")
public class UserRoleQueryBO {
    /**
     * 用戶ID
     */
    @Schema(title = "用戶ID")
    private Long userId;

    /**
     * 角色名稱
     */
    @Schema(title = "角色名稱")
    private String roleName;
}

DAO 層

接口定義

在 DAO 層創(chuàng)建接口并定義分頁查詢方法：

UserMapper.java

package com.microsun.integrated.framework.mapper;

import com.baomidou.mybatisplus.core.metadata.IPage;
import com.baomidou.mybatisplus.extension.plugins.pagination.Page;
import com.microsun.integrated.framework.domain.RoleVo;
import com.microsun.integrated.framework.domain.UserRoleQueryBO;
import org.apache.ibatis.annotations.Param;

public interface UserMapper {
    /**
     * 聯(lián)表查詢實現(xiàn)分頁，根據(jù)用戶ID查詢用戶具有的角色列表
     * 把聯(lián)表查詢得到的數(shù)據(jù)當成一張單表來看
     *
     * @param page 分頁對象
     * @param bo   查詢條件對象
     * @return 分頁后的角色列表
     */
    IPage<RoleVo> getUlserListByMulTable(@Param("page") IPage<RoleVo> page, @Param("bo") UserRoleQueryBO bo);
}

映射文件

創(chuàng)建對應的 XML 映射文件 UserMapper.xml，并在其中編寫 SQL 查詢語句：

UserMapper.xml

<?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.microsun.integrated.framework.mapper.UserMapper">
    <select id="getUlserListByMulTable" resultType="com.microsun.integrated.framework.domain.RoleVo">
        select sr.role_name
        from sys_user su
        left join sys_user_role sur on su.id = sur.user_id
        left join sys_role sr on sur.role_id = sr.id
        where su.id = #{bo.userId}
        <if test="bo.roleName != null and bo.roleName != ''">
            and sr.role_name like concat('%', #{bo.roleName}, '%')
        </if>
        <include refid="mp_limit_sql"/>
    </select>
</mapper>

這里使用 <if> 標簽來動態(tài)拼接 SQL 語句，并使用 <include refid="mp_limit_sql"/> 來引用 MyBatis-Plus 提供的分頁 SQL 語法。

Service 層

接口定義

定義 Service 接口：

UserService.java

package com.microsun.integrated.framework.service;

import com.microsun.integrated.framework.domain.PageVO;
import com.microsun.integrated.framework.domain.RoleVo;
import com.microsun.integrated.framework.domain.UserRoleQueryBO;

public interface UserService {
    /**
     * 獲取用戶角色列表
     *
     * @param currentPage 當前頁碼
     * @param pageSize    每頁數(shù)量
     * @param bo          查詢條件對象
     * @return 分頁后的角色列表
     */
    PageVO<RoleVo> getUserRoleList(int currentPage, int pageSize, UserRoleQueryBO bo);
}

實現(xiàn)類

實現(xiàn) Service 接口：

UserServiceImpl.java

package com.microsun.integrated.framework.service.impl;

import com.baomidou.mybatisplus.extension.service.impl.ServiceImpl;
import com.microsun.integrated.framework.domain.PageVO;
import com.microsun.integrated.framework.domain.RoleVo;
import com.microsun.integrated.framework.domain.UserRoleQueryBO;
import com.microsun.integrated.framework.mapper.UserMapper;
import com.microsun.integrated.framework.service.UserService;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Service;
import com.baomidou.mybatisplus.extension.plugins.pagination.Page;

import java.util.List;

@Service
public class UserServiceImpl extends ServiceImpl<UserMapper, RoleVo> implements UserService {

    @Autowired
    private UserMapper userMapper;

    @Override
    public PageVO<RoleVo> getUserRoleList(int currentPage, int pageSize, UserRoleQueryBO bo) {
        IPage<RoleVo> page = new Page<>(currentPage, pageSize);
        IPage<RoleVo> result = userMapper.getUlserListByMulTable(page, bo);

        PageVO<RoleVo> pageVO = new PageVO<>();
        pageVO.setTotal(result.getTotal());
        pageVO.setSize(result.getSize());
        pageVO.setCurrent(result.getCurrent());
        pageVO.setRecords(result.getRecords());

        return pageVO;
    }
}

Controller 層

創(chuàng)建 Controller 類來處理前端請求：

UserController.java

package com.microsun.integrated.framework.controller;

import com.microsun.integrated.framework.domain.PageVO;
import com.microsun.integrated.framework.domain.RoleVo;
import com.microsun.integrated.framework.domain.UserRoleQueryBO;
import com.microsun.integrated.framework.service.UserService;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RequestParam;
import org.springframework.web.bind.annotation.RestController;

import javax.servlet.http.HttpServletRequest;

@RestController
@RequestMapping("/users")
public class UserController {

    @Autowired
    private UserService userService;

    @GetMapping("/roles")
    public PageVO<RoleVo> getUserRoleList(
            @RequestParam(value = "currentPage", defaultValue = "1") int currentPage,
            @RequestParam(value = "pageSize", defaultValue = "10") int pageSize,
            @RequestParam(value = "userId", required = false) Long userId,
            @RequestParam(value = "roleName", required = false) String roleName) {

        UserRoleQueryBO bo = new UserRoleQueryBO(userId, roleName);
        return userService.getUserRoleList(currentPage, pageSize, bo);
    }
}

測試

現(xiàn)在你可以啟動 Spring Boot 應用并測試你的分頁聯(lián)表查詢功能?？梢酝ㄟ^發(fā)送 HTTP GET 請求到 /users/roles 來測試上述功能，例如：

GET /users/roles?currentPage=1&pageSize=2&userId=1&roleName=admin
GET /users/roles?currentPage=1&pageSize=2&userId=1

通過這個示例，你學會了如何封裝請求參數(shù)，并在 MyBatis-Plus 的 XML 文件中使用這些封裝好的參數(shù)。這有助于保持代碼的整潔性和可維護性。

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