Spring Data JPA 提供了很多强大的数据操作，本示例以Spring Boot + JPA + My SQL 来演示默认提供最基础的接口和方法对数据的操作。

演示的版本：

  1. Spring Boot 2.0.4.RELEASE
  2. My SQL 5.*

1、简介

Spring 在数据的操作上，提供以 Repository 为基础接口，CrudRepository 、PagingAndSortingRepository、JpaRepository 为子接口，作为Spring Data JPA操作的核心。
其中继承关系是 Repository <-CrudRepository <- PagingAndSortingRepository <- JpaRepository.

2、依赖

添加相关的JPA 和 数据库的连接jar包 :

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<dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-data-jpa</artifactId>
</dependency>

<dependency>
    <groupId>mysql</groupId>
    <artifactId>mysql-connector-java</artifactId>
    <scope>runtime</scope>
</dependency>

3、配置

在application.yml/application.properties 配置我们的数据连接信息：

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spring:
    datasource:
      driver-class-name: com.mysql.jdbc.Driver
      url: jdbc:mysql://127.0.0.1:3306/test?characterEncoding=utf8
      username: root
      password: #password
    jpa:
      hibernate:
        ddl-auto: update
      show-sql: true

4、 实体Entity

以但表Person作为实体类：

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package com.devnp.entity ;

import java.util.Date;

import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.Id;
import javax.persistence.Temporal;
import javax.persistence.TemporalType;

@Entity
public class Person {

    @Id
    @GeneratedValue
    private int id ;

    @Column(name = "LastName")
    private String lastName ;

    @Column(name = "FirstName")
    private String firstName ;

    @Column(name = "Age")
    private int age ;

    @Column(name = "Birth")
    @Temporal(TemporalType.DATE)
    private Date birth ;

    @Column(name = "Salary")
    private double salary ;

    public Person() {
        super();
    }


    public Person(int id) {
        super();
        this.id = id;
    }

    public Person(String lastName, String firstName, int age, Date birth, double salary) {
        super();
        this.lastName = lastName;
        this.firstName = firstName;
        this.age = age;
        this.birth = birth;
        this.salary = salary;
    }

    public int getId() {
        return id;
    }

    public void setId(int id) {
        this.id = id;
    }

    public String getLastName() {
        return lastName;
    }

    public void setLastName(String lastName) {
        this.lastName = lastName;
    }

    public String getFirstName() {
        return firstName;
    }

    public void setFirstName(String firstName) {
        this.firstName = firstName;
    }

    public int getAge() {
        return age;
    }

    public void setAge(int age) {
        this.age = age;
    }

    public Date getBirth() {
        return birth;
    }

    public void setBirth(Date birth) {
        this.birth = birth;
    }

    public double getSalary() {
        return salary;
    }

    public void setSalary(double salary) {
        this.salary = salary;
    }

    @Override
    public String toString() {
        return "Person [id=" + id + ", lastName=" + lastName + ", firstName=" + firstName + ", age=" + age + ", birth="
                + birth + ", salary=" + salary + "]";
    }


}

5、CrudRepository

CrudRepository 为我们常用的增删查改提供相应的功能，CrudPersonRepository 继承 CrudPersonRepository接口：

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package com.devnp.repository;

import org.springframework.data.repository.CrudRepository;

import com.devnp.entity.Person;

public interface CrudPersonRepository extends CrudRepository<Person, Integer> {

}

利用单元测试对其常用的方法进行测试：
CrudPersonRepositoryTests:

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package com.devnp.repository;

import java.util.ArrayList;
import java.util.Date;
import java.util.List;

import org.junit.Test;
import org.junit.runner.RunWith;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.test.context.SpringBootTest;
import org.springframework.test.context.junit4.SpringRunner;

import com.devnp.entity.Person;

@RunWith(SpringRunner.class)
@SpringBootTest
public class CrudPersonRepositoryTests {

    @Autowired
    private CrudPersonRepository crudPersonRepository;

    /**
     * 保存或者更新单个对象
     * 根据ID判断对象是否存在，然后决定进行更新或者保存
     */
    @Test
    public void testSave() {
        System.out.println(crudPersonRepository.save(new Person("DU", "LIU" , 18, new Date(), 55522.12)));
    }

    /**
     * 保存或者更新多个对象
     * 根据ID判断对象是否存在，然后决定进行更新或者保存
     */
    @Test
    public void testSaveAll() {
        List<Person> list = new ArrayList<>();

        list.add(new Person("NAME-1", "JACK" , 20, new Date(), 6000.00));
        list.add(new Person("NAME-2", "TOME" , 18, new Date(), 7000.12));

        crudPersonRepository.saveAll(list).forEach(System.out::println);
    }

    /**
     * 根据主键进行查询
     */
    @Test
    public void testFindById() {
        System.out.println(crudPersonRepository.findById(10).get());
    }

    /**
     * 根据查询全部数据
     */
    @Test
    public void testFindAll() {
        Iterable<Person> persons = crudPersonRepository.findAll();

        persons.forEach(System.out::println);
    }

    /**
     * 根据主键判断是否存在
     */
    @Test
    public void testExistsById() {
        System.out.println(crudPersonRepository.existsById(10));
    }

    /**
     * 根据主键删除记录
     * 先会根据ID去查询对象，然后在进行删除操作
     */
    @Test
    public void testDeleteById() {
        crudPersonRepository.deleteById(11);
    }

    /**
     * 根据对象进行删除
     */
    @Test
    public void testDelete() {
        crudPersonRepository.delete(new Person(12));
    }



}

6、PagingAndSortingRepository

PagingAndSortingRepository 在 CrudRepository 的基础上还提供了排序和分页查询方法，PagingPersonRepository 继承 PagingAndSortingRepository：

```java
package com.devnp.repository;

import org.springframework.data.repository.PagingAndSortingRepository;

import com.devnp.entity.Person;

public interface PagingPersonRepository extends PagingAndSortingRepository<Person, Integer> {

}

编写测试类，对相应的排序和分页进行测试 PagingPersonRepositoryTests.java：

```java
package com.devnp.repository;

import org.junit.Test;
import org.junit.runner.RunWith;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.test.context.SpringBootTest;
import org.springframework.data.domain.PageRequest;
import org.springframework.data.domain.Sort;
import org.springframework.data.domain.Sort.Direction;
import org.springframework.test.context.junit4.SpringRunner;

@RunWith(SpringRunner.class)
@SpringBootTest
public class PagingPersonRepositoryTests {

@Autowired
private PagingPersonRepository pagingPersonRepository ;

/**
 * 查询有数据，并根据条件进行排序
 */
@Test
public void testFindAllBySort() {

    pagingPersonRepository.findAll(new Sort(Direction.DESC, "id")).forEach(System.out::println);
}

/**
 * 查询有数据，并根据条件进行分页
 */
@Test
public void testFindAllByPaging() {
    pagingPersonRepository.findAll(PageRequest.of(0, 2)).forEach(System.out::println);
}

}

7、JpaRepository

继承了 PagingAndSortingRepository 在 CrudRepository 的方法同时，还引进了flush、delete*batch 这样的操作，同时也改写一个方法的参数类型。

参考

https://projects.spring.io/spring-data-jpa/

代码

spring-boot-jpa-basic