圣杯，戈姆。按父母查找孩子，按孩子查找父母

【问题标题】：Grails, gorm. Find child by parent and parent by child圣杯，戈姆。按父母查找孩子，按孩子查找父母
【发布时间】：2015-04-17 18:53:42
【问题描述】：

例如，我有父类作者：

class Author {    
    String name
    static hasMany = [
         fiction: Book, 
         nonFiction: Book
    ]
}

还有一个子类 Book：

class Book {    
    String title
    static belongsTo = [author: Author]
}

我已经为作者做了一些记录，使用：

def fictBook = new Book(title: "IT")
def nonFictBook = new Book(title: "On Writing: A Memoir of the Craft")
def a = new Author(name: "Stephen King")
             .addToFiction(fictBook)
             .addToNonFiction(nonFictBook)
             .save()

如何找到按父级的子类记录和按子级的父级记录？

【问题讨论】：

标签： grails grails-orm

【解决方案1】：

在我看来，这不是对数据建模的最佳方式。我会这样做。

class Author {    
  String name
  static hasMany = [books: Book]
}

class Book {
  String title
  BookTypes bookType
  static belongsTo = [author: Author]
}

enum BookTypes {
  FICTION,
  NON_FICTION
}

然后，您可以像这样进行查找

def author = Author.get(1)
def nonFictionByAuthor = Book.findAllByAuthorAndBookType(author, BookTypes.NON_FICTION)

你也可以这样做......

def author = Author.get(1)
def fictionBooks = author.books.findAll { it.bookType == BookTypes.FICTION }

然后反过来：

def fictionBook = Book.findByTitleAndBookType('Title001', BookTypes.FICTION)

【讨论】：