SpringBoot JPA使用Specification多表查询LEFT JOIN

1.Student

package com.frank.jpaSpecification.entity;import lombok.AllArgsConstructor;
import lombok.Data;
import lombok.NoArgsConstructor;import javax.persistence.*;/*** @author 小石潭记* @date 2020/12/12 18:32* @Description: ${todo}*/
@Entity
@Data
@AllArgsConstructor
@NoArgsConstructor
@Table(name = "t_student")
public class Student {@Idprivate Long id;private String name;private String mobile;private Integer age;@ManyToOneprivate Company company;
}

2.Company

package com.frank.jpaSpecification.entity;import lombok.AllArgsConstructor;
import lombok.Data;
import lombok.NoArgsConstructor;import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.Id;
import javax.persistence.Table;/*** @author 小石潭记* @date 2020/12/12 18:36* @Description: ${todo}*/
@Entity
@Data
@AllArgsConstructor
@NoArgsConstructor
@Table(name = "t_company")
public class Company {@Id@GeneratedValueprivate Long id;private String name;private String code;private String address;
}

3.StudentRepository

package com.frank.jpaSpecification.repository;import com.frank.jpaSpecification.entity.Student;
import org.springframework.data.jpa.repository.JpaSpecificationExecutor;
import org.springframework.data.repository.PagingAndSortingRepository;
import org.springframework.stereotype.Component;/*** @author 小石潭记* @date 2020/12/12 14:21* @Description: ${todo}*/
@Component
public interface StudentRepository extends PagingAndSortingRepository<Student, Integer>, JpaSpecificationExecutor<Student> {
}

4.StudentService

package com.frank.jpaSpecification.service;import com.frank.jpaSpecification.entity.PageStudentRequest;
import com.frank.jpaSpecification.entity.Student;
import com.frank.jpaSpecification.repository.StudentRepository;
import com.frank.jpaSpecification.specification.StudentSpecification;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.data.domain.Page;
import org.springframework.data.domain.PageRequest;
import org.springframework.stereotype.Service;/*** @author 小石潭记* @date 2020/12/12 14:22* @Description: ${todo}*/
@Service
public class StudentService {@Autowiredprivate StudentRepository studentRepository;@Autowiredprivate StudentSpecification studentSpecification;public Page<Student> getStudentList(PageStudentRequest studentRequest) {PageRequest pageRequest = PageRequest.of(studentRequest.getPageNumber(), studentRequest.getPageSize());return studentRepository.findAll(studentSpecification.getStudentSpecification(studentRequest), pageRequest);}}

5.StudentSpecification

package com.frank.jpaSpecification.specification;import com.frank.jpaSpecification.entity.*;
import org.apache.commons.lang.StringUtils;
import org.springframework.data.jpa.domain.Specification;
import org.springframework.stereotype.Component;
import org.springframework.util.CollectionUtils;import javax.persistence.criteria.Join;
import javax.persistence.criteria.JoinType;
import javax.persistence.criteria.Predicate;
import java.time.LocalDate;
import java.util.ArrayList;
import java.util.List;/*** @author 小石潭记* @date 2020/12/12 14:27* @Description: ${todo}*/
@Component
public class StudentSpecification {/*** root 就是mobile实例  root.get("name") name是属性名 不是数据库字段名* @param paramRequest* @return* */public Specification<Student> getStudentSpecification(PageStudentRequest paramRequest) {return (root, criteriaQuery, criteriaBuilder) -> {// http://localhost:8080/student?companyName=北京&pageNumber=0&pageSize=5&name=明/*// 普通的orPredicate namePre = criteriaBuilder.like(root.get("name"), "%" + paramRequest.getName() + "%");Predicate companyPre = criteriaBuilder.like(root.get("company").get("name"), "%" + paramRequest.getCompanyName() + "%");return criteriaBuilder.or(namePre, companyPre);*/// 使用左连接查询Join<Student, Company> companyJoin = root.join("company", JoinType.LEFT);Predicate namePre = criteriaBuilder.like(root.get("name"), "%" + paramRequest.getName() + "%");Predicate companyPre = criteriaBuilder.like(companyJoin.get("name"), "%" + paramRequest.getCompanyName() + "%");return criteriaBuilder.or(namePre, companyPre);};}}

6.PageStudentRequest 请求体

package com.frank.jpaSpecification.entity;import lombok.Data;
import org.springframework.format.annotation.DateTimeFormat;import java.time.LocalDate;
import java.util.List;/*** @author 小石潭记* @date 2020/12/12 14:26* @Description: ${todo}*/
@Data
public class PageStudentRequest {private Integer pageSize = 10;private Integer pageNumber = 1;private String name;private String companyName;
}

7.StudentController

package com.frank.jpaSpecification.controller;import com.frank.jpaSpecification.entity.PageStudentRequest;
import com.frank.jpaSpecification.entity.Student;
import com.frank.jpaSpecification.service.StudentService;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.data.domain.Page;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RestController;/*** @author 小石潭记* @date 2020/12/12 19:02* @Description: ${todo}*/
@RestController
@RequestMapping("/student")
public class StudentController {@Autowiredprivate StudentService studentService;@GetMappingpublic Page<Student> index(PageStudentRequest pageStudentRequest) {return studentService.getStudentList(pageStudentRequest);}}

8.测试

http://localhost:8080/student?companyName=北京&pageNumber=0&pageSize=5&name=明

student和company的sql

-- --------------------------------------------------------
-- 主机:                           127.0.0.1
-- 服务器版本:                        5.6.40 - MySQL Community Server (GPL)
-- 服务器操作系统:                      Win64
-- HeidiSQL 版本:                  8.2.0.4675
-- --------------------------------------------------------/*!40101 SET @OLD_CHARACTER_SET_CLIENT=@@CHARACTER_SET_CLIENT */;
/*!40101 SET NAMES utf8 */;
/*!40014 SET @OLD_FOREIGN_KEY_CHECKS=@@FOREIGN_KEY_CHECKS, FOREIGN_KEY_CHECKS=0 */;
/*!40101 SET @OLD_SQL_MODE=@@SQL_MODE, SQL_MODE='NO_AUTO_VALUE_ON_ZERO' */;-- 导出 test 的数据库结构
CREATE DATABASE IF NOT EXISTS `test` /*!40100 DEFAULT CHARACTER SET utf8mb4 COLLATE utf8mb4_bin */;
USE `test`;-- 导出  表 test.t_company 结构
CREATE TABLE IF NOT EXISTS `t_company` (`id` bigint(20) NOT NULL,`address` varchar(255) COLLATE utf8mb4_bin DEFAULT NULL,`code` varchar(255) COLLATE utf8mb4_bin DEFAULT NULL,`name` varchar(255) COLLATE utf8mb4_bin DEFAULT NULL,PRIMARY KEY (`id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_bin;-- 正在导出表  test.t_company 的数据：~1 rows (大约)
DELETE FROM `t_company`;
/*!40000 ALTER TABLE `t_company` DISABLE KEYS */;
INSERT INTO `t_company` (`id`, `address`, `code`, `name`) VALUES(1, '重庆', '023', '重庆沙坪坝科技公司'),(2, '成都', '028', '成都高新区有限公司'),(3, '北京', '021', '北京朝阳区科技公司');
/*!40000 ALTER TABLE `t_company` ENABLE KEYS */;-- 导出  表 test.t_student 结构
CREATE TABLE IF NOT EXISTS `t_student` (`id` bigint(20) NOT NULL AUTO_INCREMENT,`age` int(11) DEFAULT NULL,`mobile` varchar(255) COLLATE utf8mb4_bin DEFAULT NULL,`name` varchar(255) COLLATE utf8mb4_bin DEFAULT NULL,`company_id` bigint(20) DEFAULT NULL,PRIMARY KEY (`id`),KEY `FK3k0qejwy2hdw7n0qauh6vfk7l` (`company_id`),CONSTRAINT `FK3k0qejwy2hdw7n0qauh6vfk7l` FOREIGN KEY (`company_id`) REFERENCES `t_company` (`id`)
) ENGINE=InnoDB AUTO_INCREMENT=12 DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_bin;-- 正在导出表  test.t_student 的数据：~0 rows (大约)
DELETE FROM `t_student`;
/*!40000 ALTER TABLE `t_student` DISABLE KEYS */;
INSERT INTO `t_student` (`id`, `age`, `mobile`, `name`, `company_id`) VALUES(1, 18, '18000000000', '小花', 1),(2, 21, '18000000000', '小花', 2),(3, 23, '18000000010', '小明', 2),(4, 17, '18000000000', '小花', 3),(5, 22, '18000000000', '小猪', 1),(6, 25, '18000000055', '小花', 1),(7, 26, '18000000000', '小六', 3),(8, 20, '18000000785', '小花', 1),(9, 19, '18000000000', '小菊', 2),(10, 28, '18000004521', '小花', 1),(11, 19, '18000000000', '小军', 1);
/*!40000 ALTER TABLE `t_student` ENABLE KEYS */;
/*!40101 SET SQL_MODE=IFNULL(@OLD_SQL_MODE, '') */;
/*!40014 SET FOREIGN_KEY_CHECKS=IF(@OLD_FOREIGN_KEY_CHECKS IS NULL, 1, @OLD_FOREIGN_KEY_CHECKS) */;
/*!40101 SET CHARACTER_SET_CLIENT=@OLD_CHARACTER_SET_CLIENT */;

自此左连接查询完毕，左连接查询：就是已左边的表为基准，先将左表查出的数据显示出来，再显示关联的右表中查询出的数据，没有关联数据则字段值以null展示。

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SpringBoot JPA使用Specification多表查询LEFT JOIN

1.Student

2.Company

3.StudentRepository

4.StudentService

5.StudentSpecification

6.PageStudentRequest 请求体

7.StudentController

8.测试

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