ruby-on-rails - 基于多种模型的Rails Join

Question

我有四个模型:User、Product、Purchase 和 WatchedProduct。

我正在尝试获取满足以下条件之一的产品列表:

1. 我创造了产品。
2. 我买了产品。
3. 该产品是免费的，我已经对其“加注星标”或“观看”了。

这是我目前所拥有的:

class User < ActiveRecord::Base
  ...

  def special_products
    product_ids = []

    # products I created
    my_products = Product.where(:user_id => self.id).pluck(:id)
    # products I purchased
    my_purchases = Purchase.where(:buyer_id => self.id).pluck(:product_id)
    # free products I watched
    my_watched = WatchedProduct.where(:user_id =>self.id).joins(:product).where(products: { price: 0 }).pluck(:product_id)

    product_ids.append(my_products)
    product_ids.append(my_purchases)
    product_ids.append(my_watched)

    product_ids # yields something like this => [[1, 2], [], [2]]

    # i guess at this point i'd reduce the ids, then look them up again...

    product_ids.flatten!
    product_ids & product_ids
    products = []
    product_ids.each do |id|
      products.append(Product.find(id))
    end
    products

  end
end

我想要做的是获取 Product 模型列表，而不是 ID 列表或 ActiveRecord 关系列表。我对联接还很陌生，但有没有一种方法可以在一次联接中完成所有这些操作，而不是 3 个查询、减少和重新查找？

Answer 1

首先我喜欢添加一些作用域

class Product < ActiveRecord::Base
  scope :free, -> { where(price: 0) }
  scope :bought_or_created_by, lambda do |user_id|
    where('user_id = :id OR buyer_id = :id', id: user_id)
  end
end
class WatchedProduct < ActiveRecord::Base
  scope :by_user, ->(user_id) { where(user_id: user_id) }
end

然后是查询

special_products = (Product.bought_or_created_by(id) + Product.joins(:watched_products).free.merge(WatchedProduct.by_user(id)).uniq

这将使用 2 个查询返回一组独特的产品。