ruby check if data exist in database

Question

Im new with ruby on rails and I'm again blocked on something really similar as the last time.. I have a User table, a Course table and a Mark table. I can create a Mark with a user_id, a course_id and a grade.

In my models i have :

/* Mark model */
class Mark < ActiveRecord::Base
  belongs_to :user
  belongs_to :course
end

/* Course model */
class Course < ActiveRecord::Base
  has_many :marks
end

/* User model */
class User < ActiveRecord::Base
  has_many :marks
end

So what I want to do is when I created a new mark, with my form I want that my form disappear and display a button destroy ! Like this :

<% if @mark.course_ids.include?(@course.id) and @mark.user_ids.include?(user.id)
   # Button destroy
<% else %>
   <%= form_for Mark.new do |f| %>
       <%= hidden_field_tag :course_id, @course.id %>
       <%= hidden_field_tag :user_id, user.id %>
       Grade: <%= number_field_tag :grade, nil, min: 0, max: 100 %>
       <%= f.submit %>
    <% end %>
<% end %>

The goal is to avoid the form when the mark just be added previously.. But here obviously @mark.course_ids and @mark.user_ids doesn't exist !!

Thanks for you help !

Answer 1

First, I suggest you rethink your tables, maybe take a look at the many-to-many relationship.

Regarding your question, you want to know if there exists a mark that belongs to a specific course for a specific user, so you would need something like this :

Mark.where(course_id: @course.id, user_id: current_user.id).any?

This will return true if such a record exists.

Answer 2

A belongs_to association sets up a one-to-one connection with the other models. Rails then creates a singular utility method (among others) in your model.

For example, According to your model associations, a Mark belongs_to a Course and a User. Rails will create the following utility methods in your Mark model:

@mark.course
@mark.user

So the statement:

@mark.course_ids.include?(@course.id) and @mark.user_ids.include?(user.id)

is incorrect. Those methods do not exist in the Mark model.

Try this:

Controller

@marks = Mark.where(course_id: params[:id])

This will get all the marks for that course so the mark will definitely have a course associated with it (there's no need to make that check in your view).

View

Render a form for each mark:

<% @marks.each do |mark| %>
  <% unless mark.user.exists? %>
    <%= form_for Mark.new do |f| %>
      <%= hidden_field_tag :course_id, @course.id %>
      <%= hidden_field_tag :user_id, user.id %>
      Grade: #{number_field_tag :grade, nil, min: 0, max: 100}#{f.submit}
    <% end %>
  <% end %>
<% end %>