@ManyToMany 表之间的关系

Posted 2023-04-12

【中文标题】@ManyToMany 表之间的关系

【英文标题】：@ManyToMany Relationship Between Tables

【发布时间】：2020-08-14 12:36:36

【问题描述】：

我有三个独立的实体dish, kitchen, restaraunt 和链接表many。 我的问题是，如何在我的实体类中定义这种关系？

厨房模型

@Entity
@Table(name = "kitchen")
public class Kitchen 
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private long id;
    @Column(name = "kitchen_name")
    private String name;
    @Column(name = "kitchen_photo")
    private Blob photo;

碟形模型

@Entity
@Table(name = "dish")
public class Dish 
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private long id;
    @Column(name = "dish_name")
    private String dishName;
    @Column(name = "dish_photo")
    private Blob dishPhoto;

餐厅模式

 public class Restaraunt 
        @Id
        @GeneratedValue(strategy = GenerationType.IDENTITY)
        private long id;
        @Column(name = "res_name")
        private String name;
        @Column(name = "res_rating")
        private double rating;
        @Column(name = "res_address")
        private String address;
        @Column(name = "res_number")
        private String number;
        @Column(name = "res_site")
        private String site;
        @Column(name = "res_price")
        private String price;
        @Column(name = "res_photo")
        private Blob photo;

链接表 许多模型

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

    @Column(name = "res_id")
    private long res_id;
    @Column(name = "kitchen_id")
    private long kitchen_id;
    @Column(name = "dish_id")
    private long dish_id;
    @Column(name = "many_name")
    private String name;
    @Column(name = "many_rating")
    private double rating;
    @Column(name = "many_address")
    private String address;
    @Column(name = "namy_number")
    private String number;
    @Column(name = "many_site")
    private String site;
    @Column(name = "many_price")
    private String price;
    @Column(name = "many_photo")
    private Blob photo;
    @Column(name = "dish_name")
    private String dishName;
    @Column(name = "kitchen_name")
    private String kitchenName;
    @Column(name = "dish_photo")
    private Blob dishPhoto;
    @Column(name = "kitchen_photo")
    private Blob kitchePhoto;

我知道如何定义两个表之间的这种关系，但对于两个以上我不确定。 我需要创建表Many 吗？

【问题讨论】：

请参考this，它将帮助您了解关联映射。

【参考方案1】：

要理解Restaurant 将有许多菜肴 和一个Kitchen

你可以像下面这样定义关系

@Entity
public class Restaraunt 

// all other fields

@OneToMany
private Set<Dish> dishes;

@OneToOne
private Kitchen kitchen;

您可以像上面一样从一侧进行映射，也可以从两侧进行映射，即从Dish 和Kitchen 以及Dish 到Restaurant 作为ManyToOne 和Kitchen 到@987654330 @如OneToOne

我看不出有任何理由使用Many 模型。

【讨论】：

抱歉，我指的不是厨房，而是食物，比如亚洲食物、欧洲食物等。但我明白了你的想法，谢谢！

你的问题在哪里提到？您所说的食物类型应属于Dish。你可以在Dish 模型下有一个字段private String dishType，它可以达到目的。您可以在 dishType 字段中将值设置为亚洲、欧洲。