Rails-在同一模型上具有多个“ has_many through”关联

Question

I am working on a rails app that registers campers for a camp. First you sign up using your name, email, etc. Once your profile is made, you can register for a camp. If the camp is not already full, then you are immediately enrolled. If it is full, then you are put on a waitlist. Right now I have 4 models: Campers (name, email, etc.), Camps (name, location, etc.), Enrollments, and Waitlists. The idea is to have a camper be able to register to many camps, and obviously a camp having many campers enrolled or waitlisted in it. Here are my classes:

# camper.rb
has_many :enrolled_in, :class_name => 'Camps', through: :enrollments, dependent: :destroy
has_many :waitlisted_in, :class_name => 'Camps', through: :waitlists, dependent: :destroy

# camp.rb
has_many :enrolled_campers, :class_name => 'Camper', through: :enrollments
has_many :waitlisted_campers, :class_name => 'Camper', through: :waitlists

I'm having trouble with accessing these models through the views. Here is what show.html.erb looks like:

<!-- Listing camps -->
<h2>Camps</h2>
<p>
  <strong>Name:</strong>
  <%= @camper.enrolled_in.name %> <!-- This is where I get the error -->
</p>

<!-- Adding camps -->
<h2>Add a camp:</h2>
<%= form_with(model: [@camper, @camper.enrolled_in.build ]) do |form| %>
<p>
  <%= form.label :name %><br>
  <%= form.text_field :name %>
</p>
<p>
  <%= form.submit %>
</p>
<% end %>

But I'm getting the following error:

ActiveRecord::HasManyThroughSourceAssociationNotFoundError in Campers#show

Could not find the source association(s) "enrolled_in" or :enrolled_in in model Enrollment. Try 'has_many :enrolled_in, :through => :enrollments, :source => '. Is it one of camp or camper?

And I honestly can't tell what's going wrong. I'm fairly new to databases and rails, so go easy on me.

Answer 1

Look to direction of HABTM associations.

1. This will make your code cleaner.
2. You will have :after_add and :after_destroy actions that will always track model changes (even direct foreign key inserting, unlike in same named has_many callbacks.)

So.

class Camper
  has_and_belongs_to_many :waitlists, after_add: :check_camp_ready_to_start_as_example
  has_and_belongs_to_many :enrolllists
end

class Waitlist
  belongs_to :camp
  has_and_belongs_to_many :campers
end 

class Enrolllist
  belongs_to :camp
  has_and_belongs_to_many :campers
end

class Campl
  has_many :enrolllists
  has_many :waitlists
end

How to create such migrations (need to create join tables), you can read here