activerecord

问题 In my Ruby on Rails application, I have a model Instance which belongs to another model Zone . The Zone model itself belongs to Country model. I am fetching a set of Instance objects as follows: scope :thisweek, -> { joins(:zone).where(zones: {created_at: ...}).includes(:zone) I would like to join Country to Zone and Instance as well, and then sort the result Instance set based on the zone.country.name field. Anyone can help me please? 回答1: You can try the following: scope :this_week, proc do

问题 I have a stream of data, which contains categories. I want to maintain a Category table which should contain every category I encounter exactly once. I want to implement a id = Category.upsert(name) , which should be atomic (of course), and - if possible - not use stored procedures on the DB side. 回答1: The upsert gem seems to do just that - I found it while googling to see if "upsert" is a thing. 回答2: How about this: class Category < ActiveRecord::Base ... class << self def upsert(name)

问题 While running development code through Heroku console in sandbox mode, I use first_or_create to test for existence of a record: Right.where(:language => language ). where(:work_id => work_id ). where(:contact_id => contact_id ). first_or_create! The query to test for existence of the record gets an extra predicate (1=2) added to it, so the record is not found. SELECT "rights".* FROM "rights" WHERE "rights"."language" = 'ger' AND "rights"."work_id" = 625 AND "rights"."contact_id" = 1435 AND (1

问题 I'm new to Ruby & Rails... the goal is to create a User class whose primary key ( id ) is not an integer, but a GUID. I think I have the ActiveRecord end of things setup properly (not auto-generating an id column with type integer , but with column id of type string instead), and a function that can generate a GUID. The only missing piece at this point is getting Rails to initialize a new User class' with an id using the *generate_guid* function I had wrote. My question : How do I get Rails

问题 Why does this output the same record ID repeatedly, when it should be grabbing a random record each loop iteration? count = 0 while count < 20 puts "ID: " + SomeModel.where(assoc_id: 10).order("RANDOM()").limit(1).first.id.to_s count += 1 end Output: ID: 82784 ID: 82784 ID: 82784 ID: 82784 ID: 82784 I have already ensured there are sufficient records available with the query (ie more than 1). Within a console, the line by itself (outside of a loop) will return a new ID every time, so it has

问题 [10] pry(main)> r.respondents.select(:name).uniq.size (1.1ms) SELECT DISTINCT COUNT("respondents"."name") FROM "respondents" INNER JOIN "values" ON "respondents"."id" = "values"."respondent_id" WHERE "values"."round_id" = 37 => 495 [11] pry(main)> r.respondents.select(:name).uniq.length Respondent Load (1.1ms) SELECT DISTINCT name FROM "respondents" INNER JOIN "values" ON "respondents"."id" = "values"."respondent_id" WHERE "values"."round_id" = 37 => 6 Why the difference in what each query

问题 How can I find the object associated with the results of an ActiveRecord Calculation rather than a value? For example I have @parent which has many children. I would like to find the child with the maximum 'value'. I understand that I can do @parent.children.maximum(:value), but this returns the maximum value. Is there a method similar to maximum and minimum that returns the entire object instead of the value so that I can use different fields from the maximum object? 回答1: @parent.children

问题 I have a simple app and the user can filter based on three different params by category, by discipline and by target group. All params are optional. So far it works, but the controller below is a bit bloated and I also think the three if statements are a bit messy. Is there a cleaner way to do this? def index @listings = Listing.includes(:categorizations, :listing_disciplines, :listing_targets).page(params[:page]) if params[:category_id].present? && params[:category_id] != "" @category_id =

问题 I have the following associations: class Student < ApplicationRecord has_many :people_schools has_many :schools, through: :people_schools end class PeopleSchool < ApplicationRecord belongs_to :student belongs_to :school end class School < ApplicationRecord has_many :people_schools has_many :students, through: :people_schools end I am trying to get a list of students organized by their school. I have tried the following: Student.joins(:schools).all.group('schools.name') but I get the following

问题 We have an application where user sets his/her preferred date/time format. User is expected to enter datetime in configured format across the application. Now the problem is for few formats the datetime is parsed wrongly while create/update ActiveRecord . For example user has set date/time format in hh:mm dd/MM/yyyy . Now if user enters 17:00 04/05/2012 it parses it as 5 PM 5 Apr, 2012 where it should be 5 PM 4 May, 2012 1.8.7 :004 > a = Article.create!(:name => 'a1', :published_at => '17:00