Rails ActiveRecord querying - sql

Question

So I have the following three models: Assignment.rb, Submission.rb, User.rb
And here are the relationships:
class Assignment
has_many :submissions
end
class Submission
belongs_to :assignment
belongs_to :user
# submission has a boolean column called submitted with val true or false
end
class User
has_many submissions
end
I want to know how can I query the assignments that a user has not submitted (in a clean way)? If a user submits an assignment, a new submission for that assignment and user will be created.
Not sure if I provided enough info for anyone to answer, so please comment if anything else is needed.Thx!

Answer 1

The logic that #Norly Canarias is using is correct, but I would alter it to use methods on the User class, and I would also modify it to make it database-agnostic (for example, using 'submissions.submitted = true' will not work at all in Postgres).
class User < ApplicationRecord
has_many :submissions
has_many :assignments, through: :submissions
def submitted_assignments
assignments.where(submissions: {submitted: true})
end
def unsubmitted_assignments
Assignment.where.not(id: submitted_assignments)
end
end
I have tested this and it works as expected. For a user who has a Submission for Assignment 1 with submitted == true, and who has a Submission for Assignment 2 with submitted == false, and assuming there are two more Assignments (3 and 4) for which no Submission exists, you will get:
>> user.submitted_assignments.ids
#=>[1]
>> user.unsubmitted_assignments.ids
#=>[2, 3, 4]

Answer 2

I think something like this could work (I haven't tested though):
class Assignment
has_many :submissions
end
class Submission
belongs_to :assignment
belongs_to :user
end
class User
has_many :submissions
has_many :assignments, through: :submissions
end
user = User.first
submitted = user.assignments.where('submissions.submitted = true')
not_submitted = Assignment.where.not(id: submitted)
You can also make it a scope
class Assignment
has_many :submissions
scope :not_submitted_by_user, ->(user) do
where.not(id: user.assignments.where('submissions.submitted = true'))
end
end
user = User.first
not_submitted = Assignment.not_submitted_by_user(user)

Answer 3

To get all the Assignments that are not from a specific user
#assignments = Assignment.where.not(user_id: user_id)
A clean way to do it is to create a scope in the Assignment Model
class Assignment
has_many :submissions
scope :not_from_user, ->(user_id) {where.not(user_id: user_id) }
end
And then calling
#assignments = Assignment.not_from_user 1