I am trying to create a query in Rails but am having some trouble creating the correct one. Below is my models with their relationships.
class User < ActiveRecord::Base
has_and_belongs_to_many :rsvps, class_name: 'Event'
has_many :albums
end
class Event < ActiveRecord::Base
has_many :albums
has_and_belongs_to_many :attendees, class_name: 'User'
end
class Album < ActiveRecord::Base
belongs_to :user
belongs_to :event
end
I need to get all events a user has "rsvp'ed" to that they haven't uploaded an album to yet. I can find out if a user has uploaded an album to a particular event using the following:
u = User.find(1)
e = Event.find(1)
e.albums.where(user_id: u.id)
I want to be able to run this query on each of the user's rsvp'ed albums. I know I could do something like this:
u.rsvps.delete_if { |e| !e.albums.where(user_id: u.id).blank? }
However, I want to do this all in one query instead of getting the rsvps and then iterating over them and deleting them when necessary.
In order to get all events a user has rsvp'ed to but haven't uploaded an album to yet, you can use the following, which (UPDATE) now also works when a user has not uploaded any albums.
#event_ids = Album.where(user_id: u.id).pluck(:event_id))
#event_ids.empty? ? u.rsvps : u.rsvps.where("id not in (?)", #event_ids)
In addition, this query should work as well.
u.rsvps.where.not(id: Album.where(user_id: u.id).pluck(:event_id))
Related
I'm facing an Rails (and finally a pur SQL) issue.
I have 3 tables (models). Event / User / Invitation
class Event < ApplicationRecord
has_many :invitations
end
class User < ApplicationRecord
has_many :invitations
has_many :events, through: :invitations
end
class Invitation < ApplicationRecord
belongs_to :event
belongs_to :user
end
I want to list all events where a specific user does not have invitation.
Contraints (very important in my case):
I'm starting my request by Event.
Basically, I would say it's the opposite of a merge, like a merge.not(user.events).
The only solution I found is:
Event.where.not(id: user.events.pluck(:id))
But obviously, I don't like it. 2 queries that might be somehow merge into a single one.
Any idea?
use select instead of pluck, it will create sub-query instead pulling records from database. Rails ActiveRecord Subqueries
Event.where.not(id: user.events.select(:id))
In Rails, how would one conditionally associated records on a has_many_through relationship? Using the following Rails docs example:
class Physician < ApplicationRecord
has_many :appointments
has_many :patients, through: :appointments
end
class Appointment < ApplicationRecord
belongs_to :physician
belongs_to :patient
end
class Patient < ApplicationRecord
has_many :appointments
has_many :physicians, through: :appointments
end
Suppose I wanted to have an appointment reference exactly two physicians. That is, there will not be any appointment record one there is less than two physicians assigned. However, how could that appointment then reference each physician?
Example
Basically, I want to keep track of users liking other users and mutual likes between them. A connection is established when both users like each other. But I don't want a connection when only one user likes another but it is not reciprocal.
When User A likes User B. A "like" is created.
When User B likes User A. A "like" is created. A "connection" is also created.
The connection should be able to call:
connection.users
The user should be able to call:
user.likes
user.connections
The problem that I'm having is how can that relationship table know when it is mutual?
For the original question, a connection doesnt make a difference between the two users, so i would model it as a one to many relationship and validate it only has two users.
A like has two users, the liker (giver of the like) and the likee (receiver of the like). Every time you create new like, you should check if the likee also likes the liker. If likee.likes.where(likee: liker)? If yes, then create the new connection with both users.
class User < ApplicationRecord
has_many :likes
has_many :connections
end
class Like < ApplicationRecord
belongs_to :user, :foreign_key => 'liker_id'
belongs_to :user, :foreign_key => 'likee_id'
end
class Connection < ApplicationRecord
has_many :likes
has_many :users, through: likes
end
I want to add that i am not 100% sure of this as i am currently learning Rails myself. But this is what I came up with and hopefully its useful (and correct).
Let's imagine that I have a CPA tracking system.
I would have following models: an Offer, it has some Landings, each of them has multiple Links, each of the links has a bunch of Visits.
So, I what I want is DRY code, therefore offer_id column within visits table is unacceptable. The workaround here is delegated methods like this:
class Offer < ActiveRecord::Base
has_many :landings
has_many :links, through: :landings
has_many :visits, through: :landings
end
class Landing < ActiveRecord::Base
belongs_to :offer
has_many :links
has_many :visits, through: :links
end
class Link < ActiveRecord::Base
belongs_to :landing
has_many :visits
delegate :offer, to: :landing
end
class Visit < ActiveRecord::Base
belongs_to :link
delegate :landing, to: :link
delegate :offer, to: :link
end
It works nice with a single visit, e.g. visit.offer.id. But what if I need different visits associated with one offer?
The issue is that I'm unable to construct a valid query using ActiveRecord API. It might look like Visits.where(offer: Offer.first), but it doesn't work this way, saying ActiveRecord::StatementInvalid: SQLite3::SQLException: no such column: visits.offer: SELECT "visits".* FROM "visits" WHERE "visits"."offer" = 1, which is predictable.
Question: How should I organize my code to make statements like Visits.where(offer: Offer.first) work efficiently without duplicating offer_id column within visits table?
You code was organized nicely, don't need to refactor I think. You can achieve that by defining a scope in Visit like this:
class Visit < ActiveRecord::Base
scope :from_offer, -> (offer) {
joins(link: :landing).where(ladings: {offer_id: offer.id})
}
scope :from_landing, -> (landing) {
joins(:link).where(links: {landing_id: landing.id})
}
end
So the query will be:
Visit.from_offer(Offer.first)
I'm adding quiz functionality to the twitter app from the Hartl tutorial and have these Models:
User is nearly the same as the tutorial:
class User < ActiveRecord::Base
has_many :followed_users, through: :relationships, source: :followed
has_many :takens, dependent: :destroy
has_many :questions, through: :takens
end
Taken is a table of Question ids to User ids:
class Taken < ActiveRecord::Base
belongs_to :user
belongs_to :question
end
nothing interesting in Question:
class Question < ActiveRecord::Base
attr_accessible :category, :correct, :option1, :option2, :option3, :qn
end
I want to be able to show followed_users and followers in order of the number of tests they have taken. In the console this can be had through:
User.find_by_id(1).question_ids.count
Then I can do something like:
User.find_by_id(1).followers.first.question_ids.count
in the console to get the count for a single follower.
I feel like I'm almost there.
How do I sort the followers and followed_users through their 'takens' count? (I was also looking at cache_count, which at first seemed promising, but might not be what I need...)
Ruby on Rails does not provide an object oriented mechanism to perform this; you have to write the SQL yourself. In your case, I'd say that the following line SHOULD work:
User.find_by_sql("SELECT users.*, COUNT(questions.id)
AS c FROM users, questions WHERE questions.user_id = users.id
GROUP BY users.id ORDER BY c DESC")
I don't have the actual tables in front of me, so I can't be sure that this is actual valid SQL, but hopefully it should work.
EDIT: There were a few syntax errors with my SQL but they've been fixed. Note that I'm assuming that your tables are called users and questions. They may differ for you.
I have a problem with fetching data from DB, where is between models association kind through.
On my site, I have a categories, like a sports, news, weather etc. When an user is logged in and has a selected the categories, from which want to see the articles, then I would like to display only these articles.
Here's how looks like my models:
class User < ActiveRecord::Base
has_many :user_categories
has_many :categories, :through => :user_categories
end
class Category < ActiveRecord::Base
has_many :articles
has_many :user_categories
has_many :users, :through => :user_categories
end
class UserCategory < ActiveRecord::Base
belongs_to :user
belongs_to :category
end
class Article < ActiveRecord::Base
belongs_to :category
end
But I still can't find the way, how to get all articles from user's selected categories... I tried something like
Article.joins("LEFT JOIN categories ON category.id = user_categories.category_id").where('user_categories.user_id = ?', current_user.id)
I would grateful for every advice!
Thank you
Here's one way to do it:
Article.where(:category_id => current_user.categories.map {|c| c.id})
That will create 2 queries. First one will return a list of the current user's categories. Then the ruby map function will create an array containing the ids of those categories. The second query will then return a list of articles whose category_id is in the array of ids. The second query will look something like:
select articles.* from articles where articles.category_id in(1,2,3);