activerecord

问题 I have users with many posts . I want to build an SQL query that would do the following in 1 query (no subquery), and hopefully no unions if possible. I know I can do this with union but I want to learn if this can be done using only joins. I want to get a list of distinct active users who: have no posts have no approved posts Here's what I have so far: SELECT DISTINCT u.* FROM users u LEFT JOIN posts p ON p.user_id = u.id LEFT JOIN posts p2 ON p2.user_id = u.id WHERE u.status = 'active' AND

问题 I have users with many posts . I want to build an SQL query that would do the following in 1 query (no subquery), and hopefully no unions if possible. I know I can do this with union but I want to learn if this can be done using only joins. I want to get a list of distinct active users who: have no posts have no approved posts Here's what I have so far: SELECT DISTINCT u.* FROM users u LEFT JOIN posts p ON p.user_id = u.id LEFT JOIN posts p2 ON p2.user_id = u.id WHERE u.status = 'active' AND

问题 I have users with many posts . I want to build an SQL query that would do the following in 1 query (no subquery), and hopefully no unions if possible. I know I can do this with union but I want to learn if this can be done using only joins. I want to get a list of distinct active users who: have no posts have no approved posts Here's what I have so far: SELECT DISTINCT u.* FROM users u LEFT JOIN posts p ON p.user_id = u.id LEFT JOIN posts p2 ON p2.user_id = u.id WHERE u.status = 'active' AND

问题 I am struggling to find a suitable solution for what should be a simple task. Essentially I have a category model which has many posts . The post belongs to the category . I am displaying categories as part of a search form as well as a number of other places and do not want to display categories that have no associated posts. That seems kind of pointless. I managed to solve this problem by adding the following method to my category model. # Check if Category has associated results def self

问题 I have a conditional callback that triggers a job. If the manager changes, it should call the method class Employee < ActiveRecord::Base after_update :employee_manager_on_change, if: :employee_id_changed? def employee_manager_on_change EmployeeManagerChangedJob.perform_later(id) end end I'm having trouble to test this. I needed something like context 'when changing manager' do subject { user.manager = new_manager } it 'calls employee_manager_on_change' do expect { suject.run_callbacks :update

问题 I am currently working on a project with Rails 5. I want to boost the performance, so I decided to use Low-Level caching like the following: class User < ApplicationRecord has_one :profile def cached_profile Rails.cache.fetch(['Users', id, 'profile', updated_at.to_i]) do profile end end end class Profile < ApplicationRecord belongs_to :user, touch: true end It works fine respectively. But now I want to make the two caches to collaborate. What I want is that the associated object doesn't need

问题 I am currently working on a project with Rails 5. I want to boost the performance, so I decided to use Low-Level caching like the following: class User < ApplicationRecord has_one :profile def cached_profile Rails.cache.fetch(['Users', id, 'profile', updated_at.to_i]) do profile end end end class Profile < ApplicationRecord belongs_to :user, touch: true end It works fine respectively. But now I want to make the two caches to collaborate. What I want is that the associated object doesn't need

问题 I am changing the table_name_prefix during running of a rails application (might sound weird, but really that's what I want). When the table_name_prefix changes for the ActiveRecord I reset the table names ( table_name and quoted_table_name ) by calling reset_table_name , and they change.. however I have another issue. If the table name changes, after calling such a thing like count or a find the ActiveRecord object still operates with the table, which was used before. How can reach to reset

问题 I'm wanting to use UUIDs in an app I'm building and am running into a bit of a problem. Due to UUIDs (v4) not being sortable because they're randomly generated, I'm trying to override ActiveRecord::Base#first, but Rails isn't too pleased with that. It yells at me saying ArgumentError: You tried to define a scope named "first" on the model "Item", but Active Record already defined a class method with the same name. Do I have to use a different method if I want to sort and have it sort

问题 I'm wanting to use UUIDs in an app I'm building and am running into a bit of a problem. Due to UUIDs (v4) not being sortable because they're randomly generated, I'm trying to override ActiveRecord::Base#first, but Rails isn't too pleased with that. It yells at me saying ArgumentError: You tried to define a scope named "first" on the model "Item", but Active Record already defined a class method with the same name. Do I have to use a different method if I want to sort and have it sort