主流ORM框架简介

目前ORM框架非常多，目前流行的ORM框架有：

• JPA（Java Persistence API，Java持久化API），是官方提出的Java持久化规范。持久化主要是将数据存储在数据库或者磁盘文件、xml文件中，JDBC就是一种持久化机制，文件IO也是一种持久化机制。
• Hibernate，它实现了JPA规范，它对JDBC进行了轻量级的对象封装，将POJO与数据库表建立映射关系，是一个全自动的ORM框架，可以自动生成SQL语句。
• Spring Data JPA，极大简化了JPA写法，可以在几乎不用写实现的情况下，实现对数据的访问和操作，包括CRUD、分页、排序等。

Spring Data JPA

添加依赖

 <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>

单向一对多

• 一端

@Entity
@Data
public class Banner {
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private long id;
    private String name;
    private String description;
    private String img;
    private String title;


    @OneToMany(fetch = FetchType.LAZY)
    @JoinColumn(name="bannerId")
    private List<BannerItem> items;
}

• 多端

@Entity
@Data
public class BannerItem {
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;
    private String img;
    private String keyword;
    private Short type;
    private String name;

    private Long bannerId;
}

单向多对一

• 一端

@Entity
@Data
public class Banner {
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private long id;
    private String name;
    private String description;
    private String img;
    private String title;


//    @OneToMany(fetch = FetchType.LAZY)
//    @JoinColumn(name="bannerId")
//    private List<BannerItem> items;
}

• 多端

@Entity
@Data
public class BannerItem {
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;
    private String img;
    private String keyword;
    private Short type;
    private String name;

    private Long bannerId;
    @ManyToOne
    @JoinColumn(insertable = false,updatable = false,name = "bannerId")
    private Banner banner;

}

双向一对多

• 一端（关系被维护端，加mappedBy）

@Entity
@Data
public class Banner {
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private long id;
    private String name;
    private String description;
    private String img;
    private String title;


    @OneToMany(mappedBy="banner",fetch = FetchType.LAZY)
    private List<BannerItem> items;
}

• 多端(关系维护端)

@Entity
@Data
public class BannerItem {
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;
    private String img;
    private String keyword;
    private Short type;
    private String name;

    private Long bannerId;
    @ManyToOne
    @JoinColumn(insertable = false,updatable = false,name = "bannerId")
    private Banner banner;

}

单向多对多

public class Theme{
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;
    private String title;
    private String description;
    private String name;
    private String extend;
    private String entranceImg;
    private String internalTopImg;
    private Boolean online;
    private String titleImg;
    private String tplName;

    @ManyToMany(fetch = FetchType.LAZY)
    @JoinTable(name="theme_spu", joinColumns = @JoinColumn(name="theme_id")
        , inverseJoinColumns = @JoinColumn(name="spu_id"))
    private List<Spu> spuList;
}
@Entity
@Getter
@Setter
public class Spu{
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;
    private String title;
    private String subtitle;
    private Long categoryId;
    private Long rootCategoryId;
    private Boolean online;
    private String price;
    private Long sketchSpecId;
    private Long defaultSkuId;
    private String img;
    private String discountPrice;
    private String description;
    private String tags;
    private Boolean isTest;
//    private Object spuThemeImg;
    private String forThemeImg;

//    @ManyToMany(mappedBy = "spuList")
//    private List<Theme> themeList;
}

双向多对多

public class Theme{
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;
    private String title;
    private String description;
    private String name;
    private String extend;
    private String entranceImg;
    private String internalTopImg;
    private Boolean online;
    private String titleImg;
    private String tplName;

    @ManyToMany(fetch = FetchType.LAZY)
    @JoinTable(name="theme_spu", joinColumns = @JoinColumn(name="theme_id")
        , inverseJoinColumns = @JoinColumn(name="spu_id"))
    private List<Spu> spuList;
}
@Entity
@Getter
@Setter
public class Spu{
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;
    private String title;
    private String subtitle;
    private Long categoryId;
    private Long rootCategoryId;
    private Boolean online;
    private String price;
    private Long sketchSpecId;
    private Long defaultSkuId;
    private String img;
    private String discountPrice;
    private String description;
    private String tags;
    private Boolean isTest;
//    private Object spuThemeImg;
    private String forThemeImg;

    @ManyToMany(mappedBy = "spuList")
    private List<Theme> themeList;
}