缓存相关的 ActiveRecord 对象以供收集

Question

我想选择一组 ActiveRecord 对象及其belongs_to 相关对象，并完成一个查询。 IE。调用后

products = Product.joins(:image).limit(10)

在迭代products 时，我希望product.image 不会导致对数据库的另一个查询，但它的image 属性已经填充了Image 实例，而不是从先前的查询中缓存。

如何为select 构造参数，以便它选择填充相关对象所需的所有属性？或者也许我看错了方向，还有其他方法可以减少每次迭代时这些不必要的查询：

Image Load (1.0ms)  SELECT "images".* FROM "images" WHERE "images"."id" = 270783 LIMIT 1
Image Load (1.2ms)  SELECT "images".* FROM "images" WHERE "images"."id" = 121344 LIMIT 1
Image Load (1.2ms)  SELECT "images".* FROM "images" WHERE "images"."id" = 196239 LIMIT 1
Image Load (1.2ms)  SELECT "images".* FROM "images" WHERE "images"."id" = 91194 LIMIT 1 
Image Load (1.2ms)  SELECT "images".* FROM "images" WHERE "images"."id" = 116278 LIMIT 1
Image Load (1.2ms)  SELECT "images".* FROM "images" WHERE "images"."id" = 117207 LIMIT 1
Image Load (0.8ms)  SELECT "images".* FROM "images" WHERE "images"."id" = 244471 LIMIT 1
Image Load (0.8ms)  SELECT "images".* FROM "images" WHERE "images"."id" = 239287 LIMIT 1
Image Load (0.8ms)  SELECT "images".* FROM "images" WHERE "images"."id" = 15124 LIMIT 1 
Image Load (1.2ms)  SELECT "images".* FROM "images" WHERE "images"."id" = 186670 LIMIT 1

Answer 1

您想要的称为“急切加载”。您所要做的就是将您的 .joins(:image) 更改为 .includes(:image) 以获取即时加载。

products = Product.includes(:image).limit(10)

另请参阅Rails Guide on Eager Loading。