在Grails中解释属于 [英] Explain belongsTo in Grails

问题描述

从 Grails belongsTo 文档，什么是使用

  class Book {
 static belongsTo = Author 
} 
  

在Author上执行CRUD操作时，级联操作对Book的影响是什么？

编辑：

感谢您的回复，可能是我没有正确指定我的问题。我想知道 $ b

 静态belongsTo [作者：作者] 
  

vs

  static belongsTo = Author 
  

解决方案

belongsTo 如果您需要参考返回到拥有的对象，则会很有帮助。在这种情况下， Author 可能有许多 Book s。但是，也许你正在使用书籍对象，并希望提及该书籍实例的 Author 。这是获取它的好方法。

就CRUD而言，删除或更新书籍对作者 code>，但删除 Author 会删除 Book 。如果您不添加 belongsTo ，那么不会有层叠保存/更新/删除，您必须手动完成。

示例：

  def a = new作者（名称：'JK Rawling' ）
 a.addToBooks（新书（标题：'哈利波特1'））
 a.addToBooks（新书（标题：'哈利波特2'））
 a.save（） //保存作者和书籍实例
 
 a.delete（）//作者和书籍都被删除
  

编辑：

OP更新了他们的问题，我真的不确定答案会是什么。希望Burt Beckwith很快会出现！好问题，OP。

From the Grails belongsTo documentation, what is the use of

   class Book {
    static belongsTo = Author
}

What is the impact of cascading operations on Book, when CRUD operations performed on Author?

EDIT:

Thanks for your responses, may be i didn't specify my question correctly. I would like to know the difference between

 static belongsTo [author:Author]

vs

 static belongsTo = Author

解决方案

belongsTo is helpful if you need a reference back to the owning object. In this case it is likely that an Author has many Books. But maybe you're using a book object and want to mention that book instance's Author. That is a good way to get it.

As far as CRUD goes, deleting or updating the book will not do anything to the Author, but deleting the Author will delete the Book. If you don't add belongsTo then there will be no cascading saves/updates/deletes, you will have to do it manually.

Example:

def a = new Author(name: 'J.K. Rawling')
a.addToBooks(new Book(title: 'Harry Potter 1'))
a.addToBooks(new Book(title: 'Harry Potter 2'))
a.save()   // Saves author and book instances

a.delete() // Author and both books are deleted

Edit:

The OP updated their question, and I'm honestly not sure what the answer would be. Hopefully Burt Beckwith will show up soon! Good question, OP.

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