java - 如何确保对多列(mm_book_id 和 mm_author_id)应用唯一约束？

Question

我想知道是否有人对如何确保在连接表 mm_author_books 中有想法，如何确保列(mm_book_id 和 mm_author_id ) 是独一无二的？例如，我不希望表中包含 book_id 和 author_id 的重复记录，例如 1,1 和 1,1。那么如何做到这一点...

class Book {
    String title 
    static belongsTo = Author 
    static hasMany = [authors:Author]
    static mapping = { 
        authors joinTable:[name:"mm_author_books", key:'mm_book_id' ] 
    }
}

class Author { 
    String name
    static hasMany = [books:Book]
    static mapping = { 
        books joinTable:[name:"mm_author_books", key:'mm_author_id'] 
    }
}

我在“mm_author_books”域中尝试过:

class mm_author_books {

 String book_agency_name    
 static constraints = {
    book_agency_name(unique:['mm_author_id','mm_book_id'])
    }
static belongsTo = [authors:Author, books:Book]

}

但出现以下错误:

Caused by: org.codehaus.groovy.grails.validation.exceptions.ConstraintException: Exception thrown applying constraint [unique] to class [class content_hub_admin.mm_author_books] for value [[mm_author_id, mm_book_id]]: Scope for constraint [unique] of property [name] of class [class content_hub_admin.mm_author_books] must be a valid property name of same class at content_hub_admin.mm_author_books$_clinit_closure1.doCall(mm_author_books.groovy:6) at content_hub_admin.mm_author_books$_clinit_closure1.doCall(mm_author_books.groovy) ... 28 more

感谢和问候

是啊

Answer 1

类 mm_author_books(更好的名称是作者书籍关系)没有属性 mm_author_id 和 mm_book_id。试试这个:

class AuthorBookRelationship {

    String bookAgencyName

    static constraints = {
        bookAgencyName(unique:['author','book'])
    }

    static belongsTo = [author:Author, book:Book] //only one author and one book

    }
}