Grails 格雷斯，戈姆。按父查找子对象和按子对象查找父对象

例如，我有一个父类作者：

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

还有一本儿童读物：

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

我已经使用以下方法编写了一些记录：

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()

---

我怎样才能按父类查找子类记录，按子类查找父类记录？

在我看来，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 }

然后反过来说：

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

---

在我看来，这不是为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 }

然后反过来说：

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