如何将 named_association 用于 has_many_through 关系？

Question

如何写：

has_many :sales, foreign_key: :buyer_id, dependent: :destroy
has_many :purchased_books, class_name: 'Book', through: :sales, source: :book 

像这样：

has_many :purchases, class_name: 'Sale', foreign_key: :buyer_id, dependent: :destroy
has_many :purchased_books, class_name: 'Book', through: :sales, source: :book 

此时出现以下错误：

Could not find the association :sales in model User (ActiveRecord::HasManyThroughAssociationNotFoundError)

写 has_many :sales 在 foreign_key: :buyer_id 时语法不正确。

Answer 1

:through 键必须引用已定义的关联。

has_many :purchases, class_name: 'Sale', foreign_key: :buyer_id, dependent: :destroy
has_many :purchased_books, class_name: 'Book', through: :purchases, source: :book