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

问题描述

这是我的模型:

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

每个作者的每本书编号从 1 开始，然后向上递增.所以我们将有约翰·格里沙姆 (John Grisham) 的第 1、2、3 卷，乔治·马丁 (George Martin) 的第 1..5 卷等……

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...

是否有我可以对 Book 施加的唯一约束，以保证我们不会有两本书具有相同作者的相同编号?与@Column(unique = true)类似，但约束只适用于作者X编号的组合?

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?

推荐答案

使用 @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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