In my simple attendance app, there are :students, :semesters, :attendances. Attendance has columns student:references semester:references date:date present:boolean.
semester.rb
class Semester < ApplicationRecord
has_and_belongs_to_many :students
accepts_nested_attributes_for :students
end
student.rb
class Student < ApplicationRecord
has_and_belongs_to_many :semesters
has_many :attendances, dependent: :destroy
accepts_nested_attributes_for :attendances
end
attendance.rb
class Attendance < ApplicationRecord
belongs_to :semester
belongs_to :student
validates_presence_of :date
end
In the semesters#show page, I want to display each student in that semester, and each student's attendance percentage like below.
It works, but I have to filter through some :attendances that aren't associated with the semester before I start count. So my goal is to eager-load the semester, its students, and their attendances that only belong_to that semester.
This way, when I use
#semester.students.each do |student|
student.attendances
end
The .attendances method should only return those associated with that semester. Is this possible?
Here's what I got
# semesters_controller.rb
def show
#semester = Semester.includes(students: [:attendances])
.order('students.first_name')
.find params[:id]
end
# students_helper.rb
def student_attendance(student)
total = student.attendances.select { |x| x.semester_id == #semester.id }
present = total.select &:present
percent = (present.size/total.size.to_f * 100).round rescue 0
link_to student, class: 'attendance', style: "width: #{percent}%" do
<<-HTML.html_safe
<span>#{student.first_name}</span>
<span>#{percent}%</span>
HTML
end
end
I've found that using select {|x| x.semester_id == #semester.id } instead of where semester_id: #semester.id and select &:present instead of where present: true reduces the number of queries.
Anyways, is there a way that I can load the :attendances so that I don't have to go through that first filter (select {|x| x.semester_id == #semester.id })? If I don't filter like I am doing, then it will show that student's attendance percentage for ALL semesters they've ever been in, instead of just this one semester we're trying to show on the #show page.
I just don't want to be loading all that unnecessary data, nah mean? Thanks.
Looks like you already have a way of connecting an attendance directly with a semester (as belongs_to :semester is stated in your Attendance class).
Have you tried:
class Semester < ApplicationRecord
has_and_belongs_to_many :students
has_many :attendences
end
attendences = #semester.attendences
OR just:
attendences = Attendence.where(semester: params[:id])
(you can use appropriate joins/includes to reduce sql-queries)
Related
I am working on a shipping implementation for a checkout process.
My app has carts, cart_items, orders and order_items.
Weight and size of all items are in the database and I calculate total_weight in the order and cart models. I also have a shipping_service model with weightmin and weightmax for each shipping service + a postzone and land (country) model.
Now I would like to show on the shopping cart page only the shipping services which are conform to the weight of the cart or order.
I suppose my carts_controller should be something like:
class CartsController < ApplicationController
def show
#cart = Cart.find(params[:id])
#lands = Land.find(:all)
#shippingservices = Shippingservice.where('#cart.total_weight BETWEEN ? AND ?', :weightmin, :weightmax)
end
My cart model is:
class Cart < ActiveRecord::Base
attr_accessor :total_weight
has_many :cart_items
has_many :products, :through => :cart_items
has_many :lands
has_many :shipping_services, :through => :postzones
def total_weight
cart_items.inject(0) {|sum, n| n.weight * n.amount + sum}
end
end
My land model is
class Land < ActiveRecord::Base
has_many :shippingservices, :through => :postzones
has_many :postzones
has_many :carts
end
My shipping_service model is:
class Shippingservice < ActiveRecord::Base
has_many :lands, :through => :postzones
has_many :postzones
has_many :carts
has_many :orders
end
My postzone model is:
class Postzone < ActiveRecord::Base
belongs_to :shippingservice
belongs_to :land
end
The postzone table has foreign keys for lands and shipping_services.
Latter I would like to implement two selector fields: one for ship_to_countries and one for shipping_services, with the second selector being populate only with entries related to the entry selected in the first selector.
I had already this working inside the carts_controller:
#shippingservices = Shippingservice.includes(:lands, :postzones).where('postzones.land_id = ?', Land.first.id)
Which load only shipping services for a specific country into the second selector. But I do not know how to combine the two where clauses relative to weight and postzone into one query.
Any help is very much appreciated!
Thank you in advance.
The method total_weight is a ruby method which is defined in the model Cart
Then you cannot call this method within an SQL statement.
You need to calculate the total weight in the SQL statement.
You should try something like
#shippingservices = Shippingservice.joins(carts: :cart_items).where(
'(cart_items.weight * cart_items.amount) BETWEEN ? AND ?', :weightmin, :weightmax
)
I didn't try but I think it should work :)
I have a user model
class User < ActiveRecord::Base
has_many :watched_videos
has_and_belongs_to :course
end
and a course model
class Course < ActiveRecord::Base
has_many :videos
has_and_belongs_to :users
end
and a video model
class Video < ActiveRecord::Base
belongs_to :course
has_many :watched_videos
end
and my wathed video model look like
class WatchedVideo < ActiveRecord::Base
belongs_to :user
belongs_to :video
end
I want all those courses which all videos have been viewed by a user. for example. There are two courses with 2 videos each and user have seen all videos of course one and my query has to return that course. How can I implement this?
First get all users who has watched any video:
users = WatchedVideo.pluck('Distinct("user_id")')
Fetch all courses which have above users:
courses = Course.includes(:videos).where('user_id in (?)', users)
Iterate over courses to find course who's all videos are watched:
cour = []
courses.each do |c|
c.users.each do |u|
cour << c if u.wathced_videos.pluck(:video_id) == c.videos.pluck(:id)
end
end
There is scope for optimization. You can optimize this further
I'm associating users with given firms through a join table because I need to be able to have a bunch of users with every firm and vice versa.
class User
has_many :firm_connections, dependent: :destroy
has_many :firms, through: :firm_connections
end
class FirmConnection
belongs_to :user
belongs_to :firm
end
class Firm
has_many :firm_connections
has_many :users, through: :firm_connections
end
My question is, when a user hits the index page for firms, how do I scope it to only show what those users are associated with?
class FirmPolicy < ApplicationPolicy
class Scope < Scope
def resolve
if user.admin?
scope.all
else
scope.where #only the firms associated with that user
end
end
end
Do I need to create a scope at the firm level that accepts a #user? Or can I do this all directly inline? I could hack something together, but haven't wrapped my head around pundit yet, so any direction would be greatly appreciated!
like this:
def self.associated_with(user)
all.select { |m| m.users.include?(user) }
end
This should work for you
class Firm
def index
#firms = policy_scope(Firm)
end
end
class FirmPolicy < ApplicationPolicy
class Scope < Scope
def resolve
if user.admin?
scope.all
else
user.firms #only the firms associated with that user
end
end
end
end
The policy doesn't always have to call it the way that you think, it just has to return something (for scopes, almost always an ActiveRecord::Relation, for regular, true or false). You could do
scope.includes(:firm_connections).where(firm_connections: { user_id: user.id })
but that's not as readable (IMO).
I have two models lets suppose
class A < ActiveRecord::Base
has_many :bs
end
class B < ActiveRecord::Base
belogns_to :a
end
now because of some system changes I need to convert this association to many to many some thing like this
class A < ActiveRecord::Base
has_and_belongs_to_many :bs
end
class B < ActiveRecord::Base
has_and_belongs_to_many :as
end
OR
class A < ActiveRecord::Base
has_many :cs
has_many :bs, through: :cs
end
class B < ActiveRecord::Base
has_many :cs
has_many :as, through: :cs
end
class C < ActiveRecord::Base
belongs_to :a
belongs_to :b
end
what is best way to do this and most importantly I DO NOT WANT TO LOSE MY EXISTING DATA. Existing records should automatically adopt these changes. Thanks in advance.
many to many means you have connected table(model) between two other, so you could just create this one and write relation to it, after that you could remove garbage ids from B.
A, B are not good names;)
imagine you have User and Comments, and you decide that comments can have also many users, so it can look like:
class User
has_many :comments # will be changed
has_many :user_comments
end
class UserComments
belong_to :user
belong_to :comment
end
class Comment
belong_to :user # id will be removed from table and relation will be changed
has_many :user_comments
end
# as direction for import could be something like:
User.all.each do |user|
user.comments.each do |comment|
UserComments.create user: user, comment: comment
end
end
I have the following setup:
One matchdays table with a column called home_team_id and one called visitor_team_id
and a team table.
My Match model looks like this:
class Match < ActiveRecord::Base
belongs_to :home_team, class_name: "Team", foreign_key: :home_team_id
belongs_to :visitor_team, class_name: "Team", foreign_key: :visitor_team_id
belongs_to :matchday
validates :home_team, presence: true
validates :visitor_team, presence: true
end
And the Team model like that:
class Team < ActiveRecord::Base
has_many :matches
has_many :player
end
Now it's getting tricky (at least for me). I'd like to be able to call team.matches and get all of the matches for the team. Since every team has home games and also games on the road.
Currently I'm getting a ActiveRecord::StatementInvalid Error because it's looking for the team_id column in the matches table.
So if I understand correctly, what you need is just a method that returns all games where the current team is playing. This should do the trick:
class Team < ActiveRecord::Base
has_many :player
def matches
Team.where(home_team_id => self.id, foreign_key => self.id)
# This line will also work if you want to try it out.
# Team.where("home_team_id = ?", self.id).where("foreign_key = ?", self.id)
end
end
Happy coding!