尝试将书籍附加到书籍的类(class)列表时出现错误。关于为什么或我可以做些什么来解决它的任何想法?
//For each book in a class...
for (int k = 0; k < rows.size(); k++) {
Book book = new Book()
//Assign the values to a new book object
book.id = rows[k].getProperty("ISBN")
book.title = rows[k].getProperty("title")
book.author = rows[k].getProperty("author")
book.required = rows[k].getProperty("required_optional")
book.purchaseType = rows[k].getProperty("rental_purchase")
//book.purchasePrice = rows[k].getProperty("purchase_price")
//book.rentalPrice = rows[k].getProperty("rental_fee")
//Append the book to the books list object in the particular class
classes[i].books[k + 1] << book
}
最佳答案
不是通过 []
访问,而是使用 getAt
,然后 ?
运算符将起作用:
classes?.getAt(i)?.books?.getAt(k+1) << book
或
classes?.getAt(i)?.books[k+1] << book
关于exception - Grails - 无法在空对象上调用方法 getAt(),我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/14733624/