Spring boot 中Hibernate 使用

spring.jpa.properties.hibernate.hbm2ddl.auto=
有四种配置方式，分别如下：

是hibernate的配置属性，其主要作用是：自动创建、更新、验证数据库表结构。该参数的几种配置如下：

• create：每次加载hibernate时都会删除上一次的生成的表，然后根据你的model类再重新来生成新表，哪怕两次没有任何改变也要这样执行，这就是导致数据库表数据丢失的一个重要原因。
• create-drop：每次加载hibernate时根据model类生成表，但是sessionFactory一关闭,表就自动删除。
• update：最常用的属性，第一次加载hibernate时根据model类会自动建立起表的结构（前提是先建立好数据库），以后加载hibernate时根据model类自动更新表结构，即使表结构改变了但表中的行仍然存在不会删除以前的行。要注意的是当部署到服务器后，表结构是不会被马上建立起来的，是要等应用第一次运行起来后才会。
• validate：每次加载hibernate时，验证创建数据库表结构，只会和数据库中的表进行比较，不会创建新表，但是会插入新值。

在上面配置中要注意的是“spring.jpa.hibernate.ddl-auto”这个属性，它有五个value值选着分别是：
1. none 永远以数据表字段为准，不做任何修改
2. validate 加载hibernate时，验证创建数据库表结构，会和数据库中的表进行比较，不会创建新表，但是会插入新值
3. create 每次加载hibernate，重新创建数据库表结构，这就是导致数据库表数据丢失的原因
4. create-drop 加载hibernate时创建，退出是删除表结构
5. update 加载hibernate自动更新数据库结构

一个Sample，第一张图看下目录结构

JPA依赖

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

重点看下Dao包下的BookResposibility，自带的API，都不需要具体写实现

package com.example.demo.dao;

import com.example.demo.entity.Book;
import org.springframework.data.jpa.repository.JpaRepository;
import org.springframework.data.jpa.repository.Modifying;
import org.springframework.data.jpa.repository.Query;
import org.springframework.transaction.annotation.Transactional;
import java.util.List;

public interface BookRepository extends JpaRepository<Book, Long> {

    List<Book> findByAuthor(String author);

    List<Book> findAll();

    List<Book> findByName(String name);

    Book findById(long id);

    @Transactional
    @Modifying
    @Query("update Book set name = ?1  where id = ?2")
    int updateBookName(String name, long id);

}

　　

还有我的Controller文件，主要的新增，查询，查询列表，更新操作  CRUD

package com.example.demo.controller;

import com.example.demo.entity.Book;
import com.example.demo.entity.BookPo;
import com.example.demo.dao.BookRepository;
import com.example.demo.response.ResVoid;
import com.example.demo.response.Response;
import io.swagger.annotations.ApiImplicitParam;
import io.swagger.annotations.ApiOperation;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.beans.factory.annotation.Value;
import org.springframework.web.bind.annotation.*;

import java.text.SimpleDateFormat;
import java.util.Date;
import java.util.List;

@RestController
public class BookController {

    @Value("${uid}")
    String uid;

    @Autowired
    private BookRepository bookRepository;


    @ApiOperation(value = "新增书籍信息", notes = "新增书籍信息")
    @ApiImplicitParam(dataType = "BookPo", name = "bookpo", value = "新增书籍信息")
    @RequestMapping(value = "/save", method = RequestMethod.POST)
    public ResVoid save(@RequestBody BookPo bookpo) {
        Date dt = new Date();
        SimpleDateFormat sdf = new SimpleDateFormat("yyyyMMdd HH:mm:ss");
        String date = sdf.format(dt);
        String bookname = bookpo.getName();
        String bookauthor = bookpo.getAuthor();
        int booknumber = bookpo.getNumber();
        float bookprice = bookpo.getPrice();

        bookRepository.save(new Book(bookname, bookauthor, date, booknumber, bookprice, date, date, uid, uid));
        ResVoid re = new ResVoid();
        re.setCode(200);
        re.setMessage("Success");
        return re;

        //bookRepository.save(new Book("书名11", "作者", "上架时间", 100, 23, "创建时间", "更新时间", "创建uid", "更新uid"));
        //bookRepository.save(new Book("书名12", "作者", "20190504", 100, 23, "20190504", date, "3", "4"));
        //bookRepository.save(new Book("西游记10", "吴承恩", "20190504", 100, 20, "20190504", date, "2", "3"));
    }


    @ApiOperation(value = "根据作者名字或者笔名查找书籍", notes = "根据作者名字或者笔名查找书籍")
    @ApiImplicitParam(dataType = "String", name = "author", value = "根据作者名字或者笔名查找书籍", paramType = "path",required = true)
    @RequestMapping(value = "/findByAuthor/{author}", method = RequestMethod.GET)
    public Response findByAuthor(@PathVariable("author") String author) {
        List<Book> result = bookRepository.findByAuthor(author);
        System.out.println("一共有多少条呢----" + result.size());
        for (Book book : result) {
            System.out.println(book);
        }
        System.out.println("================================");
        Response re = new Response();
        re.setCode(200);
        re.setMessage("Success");
        re.setSize(result.size());
        re.setObject(result);
        return re;
    }

    @ApiOperation(value = "根据书籍名称进行找书", notes = "根据书籍名称进行找书")
    @ApiImplicitParam(dataType = "String", name = "name", value = "根据书籍名称进行找书", paramType = "path",required = true)
    @RequestMapping(value = "/findByName/{name}", method = RequestMethod.GET)
    public Response findByName(@PathVariable String name) {
        List<Book> result = bookRepository.findByName(name);

        Response re = new Response();
        re.setCode(200);
        re.setMessage("Success");
        re.setSize(result.size());
        re.setObject(result);
        return re;
    }


    @ApiOperation(value = "更新书籍信息", notes = "更新书籍信息")
    @ApiImplicitParam(dataType = "Book", name = "book", value = "更新书籍信息", required = true)
    @RequestMapping(value = "/updateBookName", method = RequestMethod.POST)
    public Response updateBookName(@RequestBody Book book) {

        int count = bookRepository.updateBookName("三国演义", 2);
        System.out.println(count);

        List<Book> result = bookRepository.findAll();

        Response re = new Response();
        re.setCode(200);
        re.setMessage("Success");
        re.setSize(result.size());
        re.setObject(result);
        return re;

    }

    @ApiOperation(value = "更新书籍信息", notes = "更新书籍信息")
    @ApiImplicitParam(dataType = "Book", name = "book", value = "更新书籍信息", required = true)
    @RequestMapping(value = "/updateBook", method = RequestMethod.POST)
    public Response updateBook(@RequestBody Book book) {

        Date dt = new Date();
        SimpleDateFormat sdf = new SimpleDateFormat("yyyyMMdd HH:mm:ss");
        String date = sdf.format(dt);

        Book book_orignial = bookRepository.findById(book.getId());

        book.setOntime(book_orignial.getOntime());
        book.setCreatuid(book_orignial.getCreatuid());
        book.setCreatedt(book_orignial.getCreatedt());
        book.setUpdatedt(date);
        book.setUpdateuid(uid);

        bookRepository.save(book);

        List<Book> result = bookRepository.findAll();

        Response re = new Response();
        re.setCode(200);
        re.setMessage("Success");
        re.setSize(result.size());
        re.setObject(result);
        return re;

    }
}