Condition:
Tutor can follow or dis-follow student
Student can follow or dis-follow tutor
Tutor and Student are two different data models.
I build a middle data model calledapplication connecting both model
Application model:
class CreateApplications < ActiveRecord::Migration
def change
create_table :applications do |t|
t.belongs_to :tutor, index: true
t.belongs_to :student, index: true
t.timestamps null: false
end
end
end
application.rb
class Application < ActiveRecord::Base
belongs_to :tutor
belongs_to :student
end
student.rb
has_many :applications, :dependent => :destroy
has_many :tutors, through: :applications
tutor.rb
has_many :applications, :dependent => :destroy
has_many :students, through: :applications
schema.rb
ActiveRecord::Schema.define(version: 20170421093747) do
create_table "applications", force: :cascade do |t|
t.integer "tutor_id"
t.integer "student_id"
t.datetime "created_at", null: false
t.datetime "updated_at", null: false
end
add_index "applications", ["student_id"], name: "index_applications_on_student_id"
add_index "applications", ["tutor_id"], name: "index_applications_on_tutor_id".......
show.html.erb
# -->show who is the follower & person who followed & How many of them
# Error :undefined method `student' for nil:NilClass
<%= #application.student.count %> #undefined method `student' for nil:NilClass
<%= #application.tutor.count % >#undefined method `student' for nil:NilClass
<%= #application.student%> #undefined method `student' for nil:NilClass
In your controller, you need to set the #application variable.
def show
#application = Application.find(params[:id])
end
I would strongly advise against naming this class Application. The word "Application" has special meaning in Rails and you will almost certainly run into conflicts. Same goes for ApplicationController.
When model has many relationship with other model you want to use plural name, i.e. tutor.students or student.tutors
UPD: Also, you didn't pass variable into view properly, check your controller.
UPD1: Also, it's meaningless to use count on application record (btw you want to rename it to something like Courses, Classes or just StudentTutor because Application.rb is the model all your models inherit from by default, same goes to ApplicationController). It always has one student and one tutor (it belongs to both models). If you want to count related records you want to find student (if you want to count his tutors) or tutor (for vise-versa)
Related
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.
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.
I cannot figure out what is wrong with my migrations, but they won't work, trying to add foreign key on products from primary key in categories
20180724203015_create_categories.rb
class CreateCategories < ActiveRecord::Migration[5.2]
def change
create_table :categories, id: false do |t|
t.string :name
t.text :description
t.integer :category_id, primary_key: true, auto_increment: true
t.timestamps
end
end
end
20180724203105_create_products.rb
class CreateProducts < ActiveRecord::Migration[5.2]
def change
create_table :products do |t|
t.string :name
t.references :category_id, foreign_key: true, index: true
t.timestamps
end
end
end
however this always ends with an error, cannot add foreign key contraint
Ruby on Rails embraces the convention over configuration principle. That means if you follow the Rails conventions things will be much easier and almost no configuration is needed.
In your migrations you decided to fight one of the Rails conventions: The primary key of a database is stored in an id column. When you decide to not follow this convention then you cannot simply use the references method anymore without telling Rails how you set up your database instead.
My advice is: Unless you have a very, very good reason, do not fight against Rails conventions. It will not only make this task (database migration) more complex, but it also increased the risk that something else needs more configuration (ActiveRecord models for example) or that things might break in gems or when you update Rails to a newer version.
That said: Change your migration to use the Rails conventions:
# 20180724203015_create_categories.rb
class CreateCategories < ActiveRecord::Migration[5.2]
def change
create_table :categories do |t| # <- create an `id` column per default
t.string :name
t.text :description
t.timestamps
end
end
end
# 20180724203105_create_products.rb
class CreateProducts < ActiveRecord::Migration[5.2]
def change
create_table :products do |t|
t.references :category, foreign_key: true # <- just name the relation
t.string :name
t.timestamps
end
end
end
The answer to this is to remove t.integer :category_id, and rely on rails' :id column for each table, references can be made with #category or with #product, and as mentioned in the comments - #category = Cateogory.find(params[:id]) or Category.find(params[:category_id]) as I believe that is how it is referenced in routes. Thank you.
I have two models:
class Word < ApplicationRecord
has_many :g_words, class_name: 'Translation', foreign_key: 'g_id'
has_many :v_words, class_name: 'Translation', foreign_key: 'v_id'
end
class Translation < ApplicationRecord
belongs_to :g, class_name: 'Word', required: true
belongs_to :v, class_name: 'Word', required: true
end
Table Translations
t.text "note", limit: 65535
t.datetime "created_at", null: false
t.datetime "updated_at", null: false
t.integer "g_id"
t.integer "v_id"
In table Words I already inserted 2 values:
id body
1 Home
2 Maison
When I create a new Translation with
g_id v_id
1 2
Then the following error appears.
The search a lot on the internet about my problem and here is a post about what I want to achieve exactly: http://www.emreakkas.com/ruby-on-rails/rails-multiple-columns-to-the-same-tables-key
I tried to implemented and failed.
I don't know whether I implented the associations wrong or I declared the wrong foreign Keys. I really don't know where to start finding the error. I hope you can help me! Thank you!
If you are looking to build a translations table this is how you would do it:
class Word < ApplicationRecord
has_many :translations
has_many :languages, through: :translations
end
class Language < ApplicationRecord
has_many :translations
has_many :words, through: :translations
end
class Translation < ApplicationRecord
belongs_to :language
belongs_to :word
end
But Rails already has a built in i18n API which handles translations that you should take a look at first before reinventing the wheel.
I have been trying to figure out why I cannot find a model in my code even though the table is in the database. The table is a cross reference table from a many to many relationship. Does active record handle this specially? The table only contains two foreign keys and audit fields. The reason I am getting even more confused is because we have other cross reference tables that I can see the model for.
look at the has_and_belongs_to_many association here.
This will not require a model but will require an entry in the migrations which you should check.
Excerpt from link, example models:
class Assembly < ActiveRecord::Base
has_and_belongs_to_many :parts
end
class Part < ActiveRecord::Base
has_and_belongs_to_many :assemblies
end
example migrations:
class CreateAssembliesAndParts < ActiveRecord::Migration
def change
create_table :assemblies do |t|
t.string :name
t.timestamps
end
create_table :parts do |t|
t.string :part_number
t.timestamps
end
create_table :assemblies_parts, id: false do |t|
t.belongs_to :assembly
t.belongs_to :part
end
end
end
This is kind of evolution of my previous question (although I changed a lot, including model names so figured I should better create another thread).. and the nature of question changed as well..
Currently I am struggling to create a form for the function
#dot2.link!(#dot)
The function works fine in console.
Here is the info from models / controllers (I tried to keep it minimal):
class User < ActiveRecord::Base
has_many :dots, :dependent => :destroy
....
end
Dot
class Dot < ActiveRecord::Base
belongs_to :user
has_many :linkages
...
def link!(new_dot)
linkages.create!(:end_id => new_dot.id)
end
...
end
Linkages:
class LinkagesController < ApplicationController
...
def create
#dot = current_user.dots.find(params[:linkages][:end_id])
#dot2 = Dot.find(params[:id])
#dot2.link!(#dot)
end
Linkages migration:
class CreateLinkages < ActiveRecord::Migration
def self.up
create_table :linkages do |t|
t.integer :start_id
t.integer :end_id
t.timestamps
end
add_index :linkages, :start_id
add_index :linkages, :end_id
add_index :linkages, [:start_id, :end_id], :unique => true
end
...
end
Now in console if I do
User.first.dots.first.link!(User.second.dots.second)
everything works fine.
How would I create a form for it (using just dot_id) as input??
Thanks!
Look up the collection_select form helper. It renders an association however you like, defaults to a Selectbox.