在多个列上创建复合唯一约束 [英] Creating a composite Unique constraints on multiple columns

问题描述

这是我的模特：

  class User {...} 
 class Book {
用户作者; 
 int number; 
} 
  

每个书籍编号从每个作者的1开始并向上递增。因此，我们将获得John Grisham的书籍1,2,3，George Martin的书籍1 ...等等...

我能有一个独特的约束吗？放在预订上，这可以保证我们没有同一作者拥有相同编号的两本书？类似于 @Column（unique = true），但约束仅适用于作者X编号的复合？使用 @UniqueConstraint ：

  @Table（
 uniqueConstraints = 
 @UniqueConstraint（columnNames = {author_id，number}）
）
 @Entity 
 class Book extends型号{
 @ManyToOne 
 @JoinColumn（name =author_id）
用户作者; 
 int number; 
} 
  

This is my model:

class User {...}
class Book {
  User author;
  int number;
}

Every book number starts at 1 per author and increments upwards. So we'll have Books 1,2,3 by John Grisham, Book 1..5 by George Martin, etc...

Is there a unique constraint I can place on Book, that would guarantee we don't have two books with the same number by the same author? Similar to @Column(unique = true), but the constraint only applies on the composite of Author X number?

解决方案

Use @UniqueConstraint:

@Table(
    uniqueConstraints=
        @UniqueConstraint(columnNames={"author_id", "number"})
)
@Entity
class Book extends Model {
   @ManyToOne
   @JoinColumn(name = "author_id")
   User author;
   int number; 
} 

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