SpringBoot整合持久层技术--（三）Spring Data JPA

简介：

　　JPA(java Persistence API)和SpringData是两个范畴的概念。spring data jpa是spring公司下的spring data项目的一个模块。 

spring data jpa定义了接口来进行持久层的编写规范，同时还大大简化了持久层的CRUD操作。 
从此可以看出，spring data jpa与jpa之间并没有直接的关系。 
jpa是由sun公司定义的持久层规范，但是jpa 并没有做任何简化，其中只有一堆接口。 
而spring data jpa中不仅有接口，还有实现类，正是这些实现类实现了CRUD操作的简化，但是实现类并不做CRUD操作。 
spring data jpa和jpa一样，虽然定义了持久层的编写规范，但是持久层的具体操作需要由第三方框架来做，它自己并不能做相应的CRUD操作。

简而言之，spring data jpa和jpa的区别： 
1、spring data jpa由spring提供 jpa由sun公司提供 
2、两者属于同一等级，都是持久层的规范，spring data jpa对CRUD操作做了简化 
两者都可以管理任何第三方持久层框架。是同一级别的。

pom.xml

　　　　<dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-data-jpa</artifactId>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-web</artifactId>
        </dependency>
        <dependency>
            <groupId>com.alibaba</groupId>
            <artifactId>druid</artifactId>
            <version>1.1.9</version>
        </dependency>
        <dependency>
            <groupId>mysql</groupId>
            <artifactId>mysql-connector-java</artifactId>
            <scope>runtime</scope>
        </dependency>

application.properties

spring.datasource.type=com.alibaba.druid.pool.DruidDataSource
spring.datasource.url=jdbc:mysql:///chapter05
spring.datasource.username=root
spring.datasource.password=123456
spring.jpa.show-sql=true
spring.jpa.database=mysql
spring.jpa.hibernate.ddl-auto=update
spring.jpa.properties.hibernate.dialect=org.hibernate.dialect.MySQL57Dialect
#spring.jpa.properties.hibernate.dialect=org.hibernate.dialect.MySQL57InnoDBDialect
#spring.jpa.properties.database=mysql
#spring.jpa.properties.hibernate.hbm2ddl.auto=update
#spring.jpa.properties.show-sql= true

实体类，controller,service,dao

@Entity(name = "t_book")
public class Book {
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Integer id;

    @Column(name = "book_name",nullable = false)
    private String name;
    private String author;
    private Float price;

    @Transient
    private String description;
    //省略getter/setter

}

@Entity表示注解的类是实体类，name值为表名，项目启动时自动生成一张表

@Id表示改属性是主键，@GeneratedValue表示主键自动生成，strategy表示主键生成策略@Transientb表示生成数据库表时属性被忽略，就是数据表没有这个字段。

@RestController
public class BookController {
    @Autowired
    BookService bookService;
    @GetMapping("/findAll")
    public void findAll() {
        PageRequest pageable = PageRequest.of(0, 2);
        Page<Book> page = bookService.getBookByPage(pageable);
        System.out.println("总页数:"+page.getTotalPages());
        System.out.println("总记录数:"+page.getTotalElements());
        System.out.println("查询结果:"+page.getContent());
        System.out.println("当前页数:"+(page.getNumber()+1));
        System.out.println("当前页记录数:"+page.getNumberOfElements());
        System.out.println("每页记录数:"+page.getSize());
    }
    @GetMapping("/search")
    public void search() {
        List<Book> bs1 = bookService.getBookByIdAndAuthor("鲁迅", 1);
        List<Book> bs2 = bookService.getBooksByAuthorStartingWith("吴");
        List<Book> bs3 = bookService.getBooksByIdAndName("西", 3);
        List<Book> bs4 = bookService.getBooksByPriceGreaterThan(30F);
        Book b = bookService.getMaxIdBook();
        System.out.println("bs1:"+bs1);
        System.out.println("bs2:"+bs2);
        System.out.println("bs3:"+bs3);
        System.out.println("bs4:"+bs4);
        System.out.println("b:"+b);
    }
    @GetMapping("/save")
    public void save() {
        Book book = new Book();
        book.setAuthor("鲁迅");
        book.setName("呐喊");
        book.setPrice(23F);
        bookService.addBook(book);
    }
}

@Service
public class BookService {

    @Autowired
    BookDao bookDao;

    public void addBook(Book book) {
        bookDao.save(book);
    }
    public Page<Book> getBookByPage(Pageable pageable) {
        return bookDao.findAll(pageable);
    }
    public List<Book> getBooksByAuthorStartingWith(String author){ return bookDao.getBooksByAuthorStartingWith(author); }
    public List<Book> getBooksByPriceGreaterThan(Float price){
        return bookDao.getBooksByPriceGreaterThan(price);
    }
    public Book getMaxIdBook(){
        return bookDao.getMaxIdBook();
    }
    public List<Book> getBookByIdAndAuthor(String author, Integer id){ return bookDao.getBookByIdAndAuthor(author, id); }
    public List<Book> getBooksByIdAndName(String name, Integer id){
        return bookDao.getBooksByIdAndName(name, id);
    }
}

public interface BookDao extends JpaRepository<Book,Integer>{
    List<Book> getBooksByAuthorStartingWith(String author);

    List<Book> getBooksByPriceGreaterThan(Float price);
   
   @Query(value = "select * from t_book where id=(select max(id) from t_book)",nativeQuery = true)
    Book getMaxIdBook();

    @Query("select b from t_book b where b.id>:id and b.author=:author")
    List<Book> getBookByIdAndAuthor(@Param("author") String author, @Param("id") Integer id);

    @Query("select b from t_book b where b.id<?2 and b.name like %?1%")
    List<Book> getBooksByIdAndName(String name, Integer id);
}

http://localhost:8080/findAll