在 git 上找了很久没有找到一个 grape 的片段缓存方案，所以才有想法自己写一个。刚刚起步开始写，很多想法还未实现。但是已经可以配合 rails 使用了。 https://github.com/u2/grape-present_cache 使用方法：

module MyApi < Grape::API
  format :json

  include Grape::Present::Cache

  resources :posts do
    desc "Return a post"
    get ":id" do
      post = Post.find(params[:id])
      car_brands = CarBrand.where(popular: true).all
      present_cache(key: "api:posts:#{post.id}", expires_in: 2.hours) do
        present :post, post, with: API::Entities::Post
      end
      present_cache(key: "v1:api:app:cars:b", expires_in: 2.hours) do
        present car_brands, with: Entities::Car::CarBrand
      end
      present ApiMeta.new, with: Entities::Meta::Base
    end
  end
end

顺便分享一下平时 grape 缓存的一个小技巧： 技巧一：

  class Product < Grape::Entity
    root 'products', 'product'
    expose :id, :photo_path, :price, :width, :height
    expose :favorites_count, as: :like_count
    expose :like do |product, options|
      if options[:favorites]
        options[:favorites].map(&:product_id).include?(product.id)
      else
        false
      end
    end
  end

class Products < Grape::API
  resource :products do

    desc "首页商品列表"
    params do
      optional :per_page, type: Integer, default: 20
      optional :sort, type: Integer, default: 0
      optional :page, type: Integer, default: 1
    end
    get do
      favorites = current_user.favorites if current_user
      case params[:sort].to_i
      when 0
        products = Product.ranking
      end
      products = products.paginate(:page => params[:page], :per_page => params[:per_page])
      present products, with: Entities::Common::Product, favorites: favorites
    end
  end

对于上面的 api，返回的 entity 里 like 字段是根据登陆用户来判断的，这样不便于将这段代码缓存。可以将 like 字段从 Product 这个 Entity 里拿出来，然后增加一个字段 like_ids，将有 like 的 id 单独返回。

present_cache(key: "v1:api:app:products:#{page}:{per_page}", expires_in: 2.hours)
  present products, with: Entities::Common::Product
end
present :like_ids, favorites.map(&:product_id)