英文:
Multiple different type associations between two entities - SpringBoot, PostgreSQL
问题
假设我有两个实体类，User（用户）和Post（帖子）。
如果我想要允许用户编写帖子，我会创建@OneToMany关联，以便一个用户可以拥有多篇帖子。
然后，如果我想要允许用户“关注”帖子，我会创建@ManyToMany关联，以便多个用户可以关注多篇帖子。
我的问题是：在同两个实体之间拥有这些不同类型的关联是否是一个良好的做法？如果不是，是否有更好的方法？
以下是示例代码：
@Entity
public class User {
@Id
@GeneratedValue(strategy = GenerationType.IDENTITY)
private Long id;
@OneToMany(mappedBy = "user")
private Set<Post> posts;
@ManyToMany
@JoinTable(
joinColumns = @JoinColumn(name = "user_id"),
inverseJoinColumns = @JoinColumn(name = "post_id"))
private Set<Post> followedPosts;
}
@Entity
public class Post {
@Id
@GeneratedValue(strategy = GenerationType.IDENTITY)
private Long id;
@ManyToOne
@JoinColumn(name = "user_id", nullable = false)
private User user;
@ManyToMany(mappedBy = "followedPosts")
private Set<User> users;
}
英文:
Let's say I have 2 entity classes, User and Post.
If I wanted to allow users to write posts, I would make @OneToMany association, so that one user can be owner of many posts.
If I then wanted to allow users to 'follow' posts, I would make @ManyToMany association, so that many users could follow many posts.
My question: is it a good practice to have these different kind of associations between the same two entities? If not, is there a better approach?
Example bellow
@Entity
public class User{
@Id
@GeneratedValue(strategy = GenerationType.IDENTITY)
private Long id;
@OneToMany(mappedBy = "user")
private Set<Post> posts;
@ManyToMany
@JoinTable(
joinColumns = @JoinColumn(name = "user_id"),
inverseJoinColumns = @JoinColumn(name = "post_id"))
private Set<Post> followedPosts;
}
@Entity
public class Post{
@Id
@GeneratedValue(strategy = GenerationType.IDENTITY)
private Post id;
@ManyToOne
@JoinColumn(name = "id", nullable = false)
private User user;
@ManyToMany(mappedBy = "followedPosts")
private Set<User> users;
}
答案1
得分: 3
可以，您可以在相同的两个表之间有多个关联。
一个表甚至可以在自身之间有多个关联，例如，Person 表可以有一个 father_id 列和一个 mother_id 列，它们都是指向自身的外键（一对多关联）。
英文:
Yes, you can have many associations between the same 2 tables.
A table can even have multiple associations back to itself, e.g. a Person table can have a father_id column and a mother_id column, both of them foreign keys (one-to-many associations) back to the Person table itself.
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