Why isn't Ruby on Rails loading my associated objects with .includes()? - mysql

Question

My Problem
I'm attempting to retrieve data through a foreign key association in my Ruby on Rails application. The data from the primary table is loaded correctly, but the associated objects are not being loaded and are always nil.
Background Info (Migrations, Database tables, and Model classes)
I'm currently working with two tables:
eval_forms
user_details
The tables are created through Rails migrations.
The user_details table is created through a single migration:
class CreateUserDetails < ActiveRecord::Migration[5.2]
def change
create_table :user_details do |t|
t.string :eduPersonPrincipalName, unique: true
t.string :DisplayName, default: 'NULL'
t.string :Email, default: 'NULL'
t.string :Role, default: 'Student'
t.boolean :hasAppointment, default: '0'
t.timestamps
end
end
def self.down
drop_table :user_details
end
end
and the eval_forms table has had a few migrations to create and update it:
class CreateEvalForms < ActiveRecord::Migration[6.1]
def change
create_table :eval_forms do |t|
t.belongs_to :form_builder, foreign_key: 'form_builder_id'
t.belongs_to :course, foreign_key: 'course_id'
t.string :Description
t.datetime :OpenDate
t.datetime :CloseDate
t.timestamps
end
end
end
class UpdateEvalForms < ActiveRecord::Migration[6.1]
def change
add_column :eval_forms, "Author_user_details_id", :bigint, null: false
add_foreign_key :eval_forms, :user_details, column: "Author_user_details_id"
add_column :eval_forms, "Year", :integer
add_column :eval_forms, "Semester", :string
add_column :eval_forms, "IsArchived", :boolean
end
end
I know that the foreign key is set up correctly as it is listed correctly in MySQL. Here's a reference from MySQL of the 2 tables and their relation:
Additionally, I've set up the model classes in my Rails app.
eval_form:
class EvalForm < ApplicationRecord
has_many :eval_forms_roles
has_many :roles, through: :eval_forms_roles
has_many :eval_forms_courses
has_many :courses, through: :eval_forms_courses
has_many :eval_responses
has_many :eval_reminders
belongs_to :user_detail
validates :formName, presence: true
validates :formData, presence: true
end
user_detail:
class UserDetail < ApplicationRecord
has_one :la_detail
has_many :eval_responses
has_many :eval_forms
end
So What's Wrong?
Lastly, here is the code to retrieve the objects from the database and the section where I'm getting my error.
My controller action:
def index
# list *all* existing evaluation forms, with options to filter by OpenDate, CloseDate, etc (todo)
#EvalForms = EvalForm.includes(:user_detail)
end
My view:
<td><%= ef.user_detail.DisplayName %></td>
My error:
NoMethodError in Evaluations::EvalForms#index
undefined method `DisplayName' for nil:NilClass
Extracted Source location: <td><%= ef.user_detail.DisplayName %></td>
Restating the problem
In conclusion, I'm really confused as to why the associated user_detail objects are not being retrieved despite my .includes() statement in the controller action. I'm pretty new to Ruby as well as Rails, but there are other sections in the application that look similar to this and work correctly so I don't see what my issue is.

Answer 1

I would start by using conventional naming which in Rails means snake_case everywhere:
class CreateUserDetails < ActiveRecord::Migration[5.2]
def change
create_table :user_details do |t|
t.string :edu_person_principal_name, unique: true
t.string :display_name
t.string :email
t.string :role, default: 'Student'
t.boolean :has_appointment, default: false # let the driver handle conversion
t.timestamps
end
end
end
class UpdateEvalForms < ActiveRecord::Migration[6.1]
def change
change_table :eval_forms do |t|
t.belongs_to :author_user_details, foreign_key: { to_table: :user_details }
t.integer :year # consider using `YEAR(4)` instead
t.string :semester
t.boolean :is_archived, default: false
end
end
end
If you continue using a strange mix of camelCase and PascalCase you will need to explicitly configure all your associations and you will lose all the advantages of convention over configuration. I would not recommend this at all unless you're stuck with a legacy database as its a surefire recipe for developer confusion and bugs.
You will also get a missing constant error if you call the PascalCase methods without an explicit recipient (self):
class EvalForm < ApplicationRecord
def short_description
# uninitialized constant Description (NameError)
Description.truncate(27, separator: ' ')
end
end
While you can fix this with self.Description.truncate(27, separator: ' ') its still very smelly.
In this case if you want to call the column author_user_details_id instead of user_details_id which is derived from the name you need to configure the assocation to use the non-conventional name:
class EvalForm < ApplicationRecord
belongs_to :user_detail, foreign_key: :author_user_details_id
end
class UserDetail < ApplicationRecord
has_many :eval_forms, foreign_key: :author_user_details_id
end
If the rest of your schema looks like this you'll have to do this across the board.