grails - Cereal ，哥伦。按 parent 找 child ，按 child 找 parent

Question

例如，我有一个父类Author:

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

和一个 child 类的书:

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

我已经使用以下方式向Author编写了一些记录:

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()

如何找到按父级分类的子级记录和按子级分类的父级记录？

Answer 1

我认为，这不是建模数据的最佳方法。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

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

您也可以做这样的事情...

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

然后相反:

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