精通 Spring Boot 系列文（8）

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Spring Data JPA

使用：將數據訪問層接口實現 JpaRepository 接口即可完成 Spring Data JPA 訪問數據。

JpaRepository 極大簡化了 JPA 作為數據訪問的代碼。

今天給大家介紹幾個案例：

1. 簡單條件查詢

2. 關聯查詢和 @Query 查詢

3. @NamedQuery 查詢

4. Specification 查詢

案例1：簡單條件的查詢

1）編輯 pom.xml 文件（與 CrudRepository 接口案例一樣）

2）編輯 application.properties 文件（與 CrudRepository 接口案例一樣）

3）創(chuàng)建 Student 持久化類

package?nx.bean;

import?java.io.Serializable;

import?javax.persistence.Entity;
import?javax.persistence.GeneratedValue;
import?javax.persistence.GenerationType;
import?javax.persistence.Id;
import?javax.persistence.Table;
//?學生
@Entity
@Table(name="tb_student")?//?學生表
public?class?Student?implements?Serializable{

????private?static?final?long?serialVersionUID?=?1L;

????@Id
????@GeneratedValue(strategy?=?GenerationType.IDENTITY)
????private?int?id;?
????private?String?name?;?//?名字
????private?String?address?;?//?地址
????private?int?age?;?//?年齡
????private?char?sex;?//?性別

????//?getXxx?&?setXxx?方法
}

4）創(chuàng)建 StudentRepository 數據訪問接口

package?nx.repository;

import?java.util.List;

import?nx.bean.Student;
import?org.springframework.data.jpa.repository.JpaRepository;

public?interface?StudentRepository?extends?JpaRepository<Student,?Integer>?{

????/**
?????*?通過學生姓名來查詢學生對象
?????*?此方法相當于JPQL語句代碼
?????*?select?s?from?Student?s?where?s.name?=??1
?????*/
????Student?findByName(String?name);

????/**
?????*?通過名字和地址查詢學生信息
?????*?此方法相當于JPQL語句代碼
?????*?select?s?from?Student?s?where?s.name?=??1?and?s.address=?2
?????*/
????List?findByNameAndAddress(String?name?,?String?address);

????/**
?????*?通過學生姓名模糊查詢學生信息?
?????*?此方法相當于JPQL語句代碼
?????*?select?s?from?Student?s?where?s.name?like??1
?????*/
????List?findByNameLike(String?name);

}

5）創(chuàng)建 StudentService 業(yè)務層類

package?nx.service;

import?java.util.List;

import?javax.annotation.Resource;

import?nx.bean.Student;
import?nx.repository.StudentRepository;
import?org.springframework.stereotype.Service;
import?org.springframework.transaction.annotation.Transactional;
@Service
public?class?StudentService?{

????//?注入數據訪問層接口對象?
????@Resource
????private?StudentRepository?studentRepository;

????//?保存所有
????@Transactional
????public?void?saveAll(List?students)?{
????????studentRepository.saveAll(students);
????}

????//?根據名字查找
????public?Student?getStuByName(String?name)?{
????????return?studentRepository.findByName(name);
????}

????//?根據名字和地址查找
????public?List?getStusByNameAndAddress(String?name,String?address)?{
????????return?studentRepository.findByNameAndAddress(name,address);
????}

????//?根據名字模糊查詢
????public?List?getStusByNameLike(String?name)?{
????????return?studentRepository.findByNameLike("%"+name+"%");
????}
}

6）創(chuàng)建 StudentController 控制器類

package?nx.controller;

import?java.util.ArrayList;
import?java.util.List;
import?javax.annotation.Resource;
import?nx.bean.Student;
import?nx.service.StudentService;
import?org.springframework.web.bind.annotation.RequestMapping;
import?org.springframework.web.bind.annotation.RestController;

@RestController
@RequestMapping("/student")
public?class?StudentController?{

????//?注入StudentService
????@Resource
????private?StudentService?studentService;

????@RequestMapping("/save")
????public?String?save()?{
????????Student?s1?=?new?Student();
????????s1.setAddress("廣州");
????????s1.setName("帥帥");
????????s1.setAge(18);
????????s1.setSex('男');

????????Student?s2?=?new?Student();
????????s2.setAddress("廣州");
????????s2.setName("花花");
????????s2.setAge(17);
????????s2.setSex('女');

????????List?students?=?new?ArrayList<>();
????????students.add(s1);
????????students.add(s2);

????????studentService.saveAll(students);
????????return?"保存student對象成功";
????}

????@RequestMapping("/name")
????public?Student?getByName(String?name)?{
????????return?studentService.getStuByName(name);
????}

????@RequestMapping("/nameAndAddress")
????public?List?getByNameAndAddress(String?name,String?address)?{
????????return?studentService.getStusByNameAndAddress(name,?address);
????}

????@RequestMapping("/nameLike")
????public?List?getByNameLile(String?name)?{
????????return?studentService.getStusByNameLike(name);
????}???
}

7）訪問測試

http://localhost:8080/student/nameLike?name=帥