如何在grails中建立一对一的双向关系？

发布于 2024-10-08 23:42:46 字数 829 浏览 4 评论 0原文

我有两个域类，并且希望它们之间具有一对一的双向关系。我写道：


class Person {

  Book book;

  String name
  Integer age
  Date lastVisit

  static constraints = {
    book unique: true  // "one-to-one". Without that = "Many-to-one".
  }

}



class Book {

  String title
  Date releaseDate
  String ISBN

  static belongsTo = [person:Person] // it makes relationship bi-directional regarding the grails-docs 
}

所以，我想要双向，我无法在生成的 SQL 中找到从 Book 到 Person 的链接：


CREATE TABLE `book` (
  `id` bigint(20) NOT NULL AUTO_INCREMENT,
  `version` bigint(20) NOT NULL,
  `isbn` varchar(255) NOT NULL,
  `release_date` datetime NOT NULL,
  `title` varchar(255) NOT NULL,
  PRIMARY KEY (`id`)
) ENGINE=MyISAM AUTO_INCREMENT=2 DEFAULT CHARSET=latin1

那么这意味着它不是双向的？怎么做成双向的？

原文

I have two domain classes and want to have one-to-one BIDIRECTIONAL relation between them. I write:


class Person {

  Book book;

  String name
  Integer age
  Date lastVisit

  static constraints = {
    book unique: true  // "one-to-one". Without that = "Many-to-one".
  }

}



class Book {

  String title
  Date releaseDate
  String ISBN

  static belongsTo = [person:Person] // it makes relationship bi-directional regarding the grails-docs 
}

So, i want to have bi-directional, i could NOT find link from Book to Person in generated SQL:


CREATE TABLE `book` (
  `id` bigint(20) NOT NULL AUTO_INCREMENT,
  `version` bigint(20) NOT NULL,
  `isbn` varchar(255) NOT NULL,
  `release_date` datetime NOT NULL,
  `title` varchar(255) NOT NULL,
  PRIMARY KEY (`id`)
) ENGINE=MyISAM AUTO_INCREMENT=2 DEFAULT CHARSET=latin1

So then it means it is not bidirectional then? How to make bidirectional?

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单挑你×的.吻 2024-10-15 23:42:46

检查 hasOne 属性，在哪个类中定义 hasOne 和 BelongsTo 取决于您希望存储 FK 的位置，检查有关 hasOne 的 grails 文档：
http://www.grails.org/doc/latest/参考/Domain%20Classes/hasOne.html

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一张白纸 2024-10-15 23:42:46

要使这种关系成为一对一的双向关系，您应该将它们定义为fallows

     //Person is the owning side of relationship
     class Person {

      //a foreign key will be stored in Book table called person_id
      static hasOne = [book:Book]

      static constraints = {
        book unique: true
      }  
    }

    Class Book{
     Person person
    }

ownTo 用于指定一对多、多对一或多对多关系的所有者方（管理关系），并且为了建立双向关系，

belongsTo 应该始终在拥有方使用

To make this relationship one to one bidirectional,you should define them as fallows

     //Person is the owning side of relationship
     class Person {

      //a foreign key will be stored in Book table called person_id
      static hasOne = [book:Book]

      static constraints = {
        book unique: true
      }  
    }

    Class Book{
     Person person
    }

belongsTo is used for specifying the owner side(which manages relationship) of a one-to-many, many-to-one, or many-to-many relationship and for making relationship bidirectional

belongsTo should be used always in owned side

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