如何讓我的模型，利用我的緩存中保存時？

Question

我使用Rails 5.我有以下型號

class MyObject < ActiveRecord::Base 
    ... 
    belongs_to :distance_unit 

    ... 
    def save_with_location 
    transaction do 
     address = LocationHelper.get_address(location) 
     if !self.address.nil? && !address.nil? 
     self.address.update_attributes(address.attributes.except("id", "created_at", "updated_at")) 
     elsif !address.nil? 
     address.race = self 
     address.save 
     end 

     # Save the object 
     save 
    end 
    end 

通過一些狡猾的調試，我想通了，「保存」方法導致此查詢被執行...

DistanceUnit Load (0.3ms) SELECT "distance_units".* FROM "distance_units" WHERE "distance_units"."id" = $1 LIMIT $2 [["id", 2], ["LIMIT", 1]] 
    ↳ app/models/my_object.rb:54:in `block in save_with_location' 

這heppens上述各方法被調用的時間。這不是最佳的，因爲我已經將我的DistanceUnit模型設置爲具有緩存。以下是它的代碼。如何讓我的「保存」方法自動使用緩存而不是每次都執行此查詢？

class DistanceUnit < ActiveRecord::Base 

    def self.cached_find_by_id(id) 
    Rails.cache.fetch("distanceunit-#{id}") do 
     puts "looking for id: #{id}" 
     find_by_id(id) 
    end 
    end 

    def self.cached_find_by_abbrev(abbrev) 
    Rails.cache.fetch("distanceunit-#{abbrev}") do 
     find_by_abbrev(abbrev) 
    end 
    end 

    def self.cached_all() 
    Rails.cache.fetch("distanceunit-all") do 
     all 
    end 
    end 

end 

Answer 1

導軌5使得this change後默認需要belongs_to關聯。這意味着關聯記錄必須在數據庫中存在，否則驗證將失敗。有解決從緩存中保存MyObject實例之前手動設置distance_unit防止數據庫中獲取它的問題

1）的幾個可能的方式：

def save_with_location 
     # ... 

     # Save the object 
     self.distance_unit = DistanceUnit.cached_find_by_id(self.distance_unit_id) 
     save 
    end 
    end 

2）或選擇退出此行爲：

你可以通過optional: true到belongs_to協會，將刪除此驗證檢查：

class MyObject < ApplicationRecord 
    # ... 
    belongs_to :distance_unit, optional: true 
    # ... 
end 

Answer 2

說實話，我覺得有一個不好的設計

距離計算中的一個建議使用另一種方法

道具：

• 沒有必要
• SOLID
• 沒有自我緩存寫入在模型邏輯

距離計算邏輯的代碼如下：

require 'active_record' 

ActiveRecord::Base.logger = Logger.new STDOUT 

class Address < ActiveRecord::Base 
    establish_connection adapter: 'sqlite3', database: 'foobar.db' 
    connection.create_table table_name, force: true do |t| 
    t.string :name 
    t.decimal :latitude, precision: 15, scale: 13 
    t.decimal :longitude, precision: 15, scale: 13 
    t.references :addressable, polymorphic: true, index: true 
    end 

    belongs_to :addressable, polymorphic: true 
end 

class Shop < ActiveRecord::Base 
    establish_connection adapter: 'sqlite3', database: 'foobar.db' 
    connection.create_table table_name, force: true do |t| 
    t.string :name 
    end 

    has_one :address, as: :addressable 
end 

class House < ActiveRecord::Base 
    establish_connection adapter: 'sqlite3', database: 'foobar.db' 
    connection.create_table table_name, force: true do |t| 
    t.string :name 
    end 

    has_one :address, as: :addressable 
end 

class Measure 
    def initialize address_from, address_to 
    @address_from = address_from 
    @address_to = address_to 
    end 

    def distance 
    # some calculation logic 
    lat_delta = @address_from.latitude - @address_to.latitude 
    lon_delta = @address_from.longitude - @address_to.longitude 
    lat_delta.abs + lon_delta.abs 
    end 

    def units 
    'meters' 
    end 
end 

shop_address = Address.new name: 'Middleberge FL 32068', latitude: 30.11, longitude: 32.11 
house_address = Address.new name: 'Tucson AZ 85705-7598', latitude: 40.12, longitude: 42.12 
shop = Shop.create! name: 'Food cort' 
house = House.create! name: 'My home' 
shop.update! address: shop_address 
house.update! address: house_address 
p 'Shop:', shop 
p 'House:', house 
measure = Measure.new shop_address, house_address 
p "Distance between #{shop.name} (#{shop.address.name}) and #{house.name} (#{house.address.name}): #{measure.distance.to_s} #{measure.units}" 

你可以運行它：$ ruby path_to_file.rb

而且結果應該如下：

"Shop:" 
#<Shop id: 1, name: "Food cort"> 
"House:" 
#<House id: 1, name: "My home"> 
"Distance between Food cort (Middleberge FL 32068) and My home (Tucson AZ 85705-7598): 20.02 meters"