07, operation of the database by springdata jpa

Us on one of springboot build a simple application, which will introduce the use of a spring-data-jpa operation of the database.

Create a new MySQL database, where the database called springboot, establish user_info data table, as the table object example of our operations.

user_info information is as follows:

DROP TABLE IF EXISTS `user_info`;
CREATE TABLE `user_info` (
  `id` int(11) NOT NULL AUTO_INCREMENT,
  `username` varchar(255) DEFAULT NULL,
  `password` varchar(255) DEFAULT NULL,
  PRIMARY KEY (`id`)
) ENGINE=MyISAM AUTO_INCREMENT=3 DEFAULT CHARSET=utf8;

-- ----------------------------
-- Records of user_info
-- ----------------------------
INSERT INTO `user_info` VALUES ('1', 'Java之音', '12345');
INSERT INTO `user_info` VALUES ('2', '张无忌', '123');

　　

After a successful database and table creation, back to our project

Step Zero, first introduced in MySQL and jpa maven dependencies:

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

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

　　

The first step, configure the database connection information in the yml configuration file:

spring:
  datasource:
    driver-class-name: com.mysql.jdbc.Driver
    url: jdbc:mysql://localhost:3306/springboot?useUnicode=true&characterEncoding=UTF-8&useSSL=false
    username: root
    password: 1011
  jpa:
    show-sql: true

　　

Next, create an entity class, the corresponding data entity mapping table:

package com.javazhiyin;

import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.GenerationType;
import javax.persistence.Id;

/**
* Created by 57783 on 2018/7/4.
*/
@Entity
public class UserInfo {

    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Integer id;

    private String username;

    private String password;

    public Integer getId() {
        return id;
    }

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

    public String getUsername() {
        return username;
    }

    public void setUsername(String username) {
        this.username = username;
    }

    public String getPassword() {
        return password;
    }

    public void setPassword(String password) {
        this.password = password;
    }

    public UserInfo(){

    }
}

　　

The third step is to create a Repository class that inherits JpaRepository categories:

package com.javazhiyin;

import org.springframework.data.jpa.repository.JpaRepository;

/**
* Created by 57783 on 2018/7/4.
*/
public interface UserInfoRepository extends JpaRepository<UserInfo,Integer>{

}

　　

Here inherited JpaRepository class that encapsulates some of the basic method of database operations, we look through the source code JpaRepository What are some ways:

//
// Source code recreated from a .class file by IntelliJ IDEA
// (powered by Fernflower decompiler)
//

package org.springframework.data.repository;

import java.util.Optional;

@NoRepositoryBean
public interface CrudRepository<T, ID> extends Repository<T, ID> {
    <S extends T> S save(S var1);

    <S extends T> Iterable<S> saveAll(Iterable<S> var1);

    Optional<T> findById(ID var1);

    boolean existsById(ID var1);

    Iterable<T> findAll();

    Iterable<T> findAllById(Iterable<ID> var1);

    long count();

    void deleteById(ID var1);

    void delete(T var1);

    void deleteAll(Iterable<? extends T> var1);

    void deleteAll();
}

　　

The fourth step, a new Controller, additions and deletions to achieve the change to the database search operation:

package com.javazhiyin;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.web.bind.annotation.*;

import java.util.List;

/**
* Created by 57783 on 2018/7/4.
*/
@RestController
public class UserInfoController {

    @Autowired
    private UserInfoRepository userInfoRepository;

    /**
     * 查
     * @return
     */
    @GetMapping(value = "/list")
    public List<UserInfo> getUserList(){
        return userInfoRepository.findAll();
    }

    /**
     * 增
     * @param username
     * @param password
     * @return
     */
    @PostMapping(value = "/addUser")
    public UserInfo addUser(@RequestParam("username") String username,
                            @RequestParam("password") String password){
        UserInfo user = new UserInfo();
        user.setUsername(username);
        user.setPassword(password);
        return userInfoRepository.save(user);
    }

    /**
     * 改
     * @param id
     * @param username
     * @param password
     * @return
     */
    @PutMapping(value = "updUser/{id}")
    public UserInfo updUser(@PathVariable("id") Integer id,
                        @RequestParam("username") String username,
                        @RequestParam("password") String password){
        UserInfo user = new UserInfo();
        user.setId(id);
        user.setUsername(username);
        user.setPassword(password);
        return userInfoRepository.save(user);

    }

    /**
     * 删
     * @param id
     */
    @DeleteMapping(value = "delUser/{id}")
    public void delUser(@PathVariable("id") Integer id){
        UserInfo user = new UserInfo();
        user.setId(id);
        userInfoRepository.delete(user);
    }

}

　　

Test the code above, here we use postman test is very easy:

Query test:

New test:

 

Modify the test:

 

Delete the test:

 

We can see through all the tests, springboot using spring-data-jpa CRUD operations were indeed very convenient.

 

a few questions:

 

1, annotation objects @GeneratedValue entity mapping class concept and usage?

 

JPA requires each entity Entity, you must have one and only one primary key, and @GeneratedValue annotations to generate the primary key is a unique identifier of an entity.

JPA provides four primary key generation strategy is defined in an enumeration class GenerationType, respectively:

1. GenerationType.TABLE
2. GenerationType.SEQUENCE
3. GenerationType.IDENTITY
4. GenerationType.AUTO

 

GenerationType.TABLE

使用一个特定的数据库表格来保存主键,持久化引擎通过关系数据库的一张特定的表格来生成主键。这种策略的好处是不依赖于外部环境和数据库的具体实现，在不同数据库间可以很容易的进行移植。但由于其不能充分利用数据库的特性，所以不会优先使用。

 

GenerationType.SEQUENCE

在某些数据库中不支持主键自增长，比如Oracle。其提供了一种叫做”序列(sequence)”的机制生成主键。此时，GenerationType.SEQUENCE就可以作为主键生成策略。该策略的不足之处正好与TABLE相反，由于只有部分数据库(Oracle,PostgreSQL,DB2)支持序列对象，所以该策略一般不应用于其他数据库。

 

GenerationType.IDENTITY

主键自增长策略，数据库在插入数据时，会自动给主键赋值,比如MYSQL可以在创建表时声明”auto_increment” 来指定主键自增长。该策略在大部分数据库中都提供了支持(指定方法或关键字可能不同)，但还是有少数数据库不支持，所以可移植性略差。

 

GenerationType.AUTO

把主键生成策略交给持久化引擎(persistence engine)，持久化引擎会根据数据库在以上三种主键生成策略中选择其中一种。此种主键生成策略比较常用，由于JPA默认的生成策略就是GenerationType.AUTO，所以使用此种策略时可以显式的指定@GeneratedValue(strategy = GenerationType.AUTO)也可以直接@GeneratedValue。

 

2、Spring Data JPA提供了哪些接口，可以实现哪些功能？

 

1. Repository：最顶层的接口，是一个空的接口，目的是为了统一所有Repository的类型，且能让组件扫描的时候自动识别。
2. CrudRepository ：是Repository的子接口，提供CRUD的功能
3. PagingAndSortingRepository：是CrudRepository的子接口，添加分页和排序的功能
4. JpaRepository：是PagingAndSortingRepository的子接口，增加了一些实用的功能，比如：批量操作等。
5. JpaSpecificationExecutor：用来做负责查询的接口
6. Specification：是Spring Data JPA提供的一个查询规范，要做复杂的查询，只需围绕这个规范来设置查询条件即可

 

原文;https://www.cnblogs.com/javazhiyin/p/9297743.html