验证触发创建关系

Question

模型我在我的应用2种型号，User和Notification，像这样：

class Notification < ActiveRecord::Base 
    has_and_belongs_to_many :users 

    validates_presence_of :content, on: :create 
end 
class User < ActiveRecord::Base 
    has_and_belongs_to_many :notifications 

    validates_presence_of :email 
    validates_uniqueness_of :email 
end 

每当我要创建一个新的通知，我使用下面的代码：

​​

这工作正常，但我看到很多数据库检查日志。这是正常的吗？有什么我可以做的，以降低数据库访问量？

日志片段：

User Load (2.1ms) SELECT DISTINCT "users".* FROM "users" WHERE "users"."kind" IN ('parent', 'student', 'teacher') 
    (0.1ms) begin transaction 
User Exists (0.1ms) SELECT 1 AS one FROM "users" WHERE ("users"."email" = '[REDACTED]' AND "users"."id" != 34) LIMIT 1 
User Exists (0.1ms) SELECT 1 AS one FROM "users" WHERE ("users"."email" = '[REDACTED]' AND "users"."id" != 36) LIMIT 1 
User Exists (0.1ms) SELECT 1 AS one FROM "users" WHERE ("users"."email" = '[REDACTED]' AND "users"."id" != 38) LIMIT 1 
User Exists (0.1ms) SELECT 1 AS one FROM "users" WHERE ("users"."email" = '[REDACTED]' AND "users"."id" != 40) LIMIT 1 
... 

SQL (0.4ms) INSERT INTO "notifications" ("content", "created_at", "updated_at") VALUES (?, ?, ?) [["content", "asdadasd"], ["created_at", "2016-03-05 13:18:27.285540"], ["updated_at", "2016-03-05 13:18:27.285540"]] 

SQL (0.2ms) INSERT INTO "notifications_users" ("user_id", "notification_id") VALUES (?, ?) [["user_id", 34], ["notification_id", 843]] 
SQL (0.1ms) INSERT INTO "notifications_users" ("user_id", "notification_id") VALUES (?, ?) [["user_id", 36], ["notification_id", 843]] 
SQL (0.1ms) INSERT INTO "notifications_users" ("user_id", "notification_id") VALUES (?, ?) [["user_id", 38], ["notification_id", 843]] 
SQL (0.1ms) INSERT INTO "notifications_users" ("user_id", "notification_id") VALUES (?, ?) [["user_id", 40], ["notification_id", 843]] 
... 

Answer 1

在我看来，第一个问题是您加载所有用户要发送一个新的通知

iethis行每次：

users = User.where(kind: params[:kinds]) 

然后，您将更多用户添加到此对象，每次查找都会导致db调用以确定用户是否已经存在。

您应该将所有用户ID都检索到一个散列，然后添加到该散列（如果没有）。接下来，根据这个散列中的这些id发送你的通知。