SpringBoot 中集成JPA

https://blog.csdn.net/forezp/article/details/70545038

• 引入jpa依赖
• 配置jpa选项
• 修改实体类，引入注解
• 修改接口

  <dependency> <groupId>org.springframework.boot</groupId> <artifactId>spring-boot-starter-data-jpa</artifactId> </dependency> spring.jpa.database-platform= org.hibernate.dialect.MySQL5Dialect jpa.hibernate.show-sql= true @lombok.Data @Entity @Table(name="fuser") public class User{ @Id @GeneratedValue(strategy = GenerationType.IDENTITY) private String id; public interface UserMapper extends JpaRepository<User, Long>{

注意事项

1. 如果是Mysql且设置了数据库的数字自增的话，在主键字段需要添加GenerationType.IDENTITY注释
2. 输出打印SQL配置： spring.jpa.show-sql= true
3. @Column 默认驼峰法不需要特别声明 比如 private Integer numberOfPages; 对应 number_of_pages，则不需要特别声明

高级用法示例

1. 分页查询和多字段的between and查询

   Pageable pageable = new PageRequest(page.getP_pageNumber()-1,page.getP_pagesize()); Page<Record> pages=recordDao.findByHolderNameAndTimesBetweenOrderByTimesDesc(search.getUsername(),qssj,jssj, pageable); list=pages.getContent();

JPA的多表关联

有github源码、blog讲解
http://niocoder.com/2018/02/28/JPA%E5%85%B3%E7%B3%BB%E6%98%A0%E5%B0%84%E7%B3%BB%E5%88%97%E4%B8%80-one-to-one%E5%A4%96%E9%94%AE%E5%85%B3%E8%81%94/

作用

通过注解配置和外键的设置

1. 实现自动的关联查询，查询A可以不需要写额外的sql获取到B或者B集合的实体类
2. 实现级联操作，新增、修改、删除（对主键主体有效）

常用注解

1. JoinColumn
   @JoinColumn(name=”address_id”, referencedColumnName=”ref_id”)

• 第一个属性是本类的属性，referencedColumnName是关联表的属性，如果不写的话就是ID了
• 如果设置了外键关联，则可以不需要设置JoinColumn字段

一对一（反向关联）

• Book主类（id,name,book_detail_id),设置了外键对BookDetail

  @Entity @Data @Table(name = "book") public class Book { @Id @GeneratedValue(strategy = GenerationType.AUTO) private int id; private String name; @OneToOne(cascade = CascadeType.ALL) private BookDetail bookDetail; public Book() { } }

• BookDetail类(id ,numberOfPages)，设置了反向关联mappedBy

  @Entity @Table(name = "book_detail") @Data public class BookDetail { @Id @GeneratedValue(strategy = GenerationType.AUTO) private Integer id; private Integer numberOfPages; @OneToOne(mappedBy = "bookDetail") private Book book; public BookDetail() {} }

• 设置了反向关联，可以通过从类找到主类,通过detail类可以找到 Book类

  public void findBookDetailsTest() throws Exception{ BookDetail detail=detailRepository.findOne(4); System.out.println(detail.getNumberOfPages()); }

一对多

• Book表 多个对应一个BookCategory，需要有book_category_id字段

  @Data @Entity public class Book { @Id @GeneratedValue(strategy = GenerationType.AUTO) private int id; private String name; @ManyToOne @JoinColumn(name = "book_category_id") private BookCategory bookCategory; public Book(){} } CREATE TABLE `book` ( `id` int(11) unsigned NOT NULL AUTO_INCREMENT, `name` varchar(255) DEFAULT NULL, `book_category_id` int(11) unsigned DEFAULT NULL, PRIMARY KEY (`id`)) ENGINE=InnoDB DEFAULT CHARSET=utf8;

• BookCategory,注意category表不需要有book字段，但是可以直接获取到Set

  @Data @Entity @Table(name = "book_category") public class BookCategory { @Id @GeneratedValue(strategy = GenerationType.AUTO) private int id; private String name; @OneToMany(mappedBy = "bookCategory", cascade = CascadeType.ALL) private Set<Book> books; public BookCategory(){} } CREATE TABLE `book_category` ( `id` int(11) unsigned NOT NULL AUTO_INCREMENT, `name` varchar(255) NOT NULL, PRIMARY KEY (`id`,`name`) ) ENGINE=InnoDB AUTO_INCREMENT=9 DEFAULT CHARSET=utf8;

多对多

通过JoinTable和MangToMany来实现，分别需要构建中间表和关联字段来实现

@Entity
@Table(name="fuser")
public class User{
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private String id;
    private String username;
    
    @ManyToMany
    @JoinTable(name = "user_role", joinColumns = { @JoinColumn(name = "userId") }, inverseJoinColumns ={@JoinColumn(name = "roleId") })
    private List<Role> roleList;
}

JPA中nativeQuery的使用

https://blog.csdn.net/qq_26819733/article/details/79661924
比如含有transient字段的时候，需要转换成实体类

@Query(value = "select a.*,b.name as product_name from wx_ib a join user_ib b on a.system_id=b.serial_number where b.user_id=?1", nativeQuery = true)
public List<Object> findByUserId(int userId);
public List<IBUser> findByUserId(int userId){
	List<Object> list=ibDao.findByUserId(userId);
	List<IBUser> result=new ArrayList();
	 for (int i = 0; i < list.size(); i++) {
            Object[] col = (Object[]) list.get(i);
            IBUser ibuser = new IBUser((String) col[2], (String) col[3]);
            result.add(ibuser);
            System.out.println(ibuser.getProductName());
        }
	return result;
}