Creating a has_and_belongs_to_many relationship in Rails - ruby-on-rails

Question

I have a User model which is designed after the Michael Hartl RoR tutorial and I am trying to create a new Teacher model. I would like the teacher to have many users but each user to have only one teacher. I created the teacher model with
class CreateTeachers < ActiveRecord::Migration
def change
create_table :teachers do |t|
t.string :name
t.string :email
t.string :phone
t.references :user, index: true, foreign_key: true
t.timestamps null: false
end
end
end
and added has_one :teacher to user.rb. Here is the teachers.rb model
class Teacher < ActiveRecord::Base
has_and_belongs_to_many :users
validates :user_id, presence: true
before_save :downcase_email
validates :name, presence: true,
length: { maximum: 50 }
VALID_EMAIL_REGEX = /\A[\w+\-.]+#[a-z\d\-]+(\.[a-z\d\-]+)*\.[a-z]+\z/i
validates :email, presence: true,
length: { maximum: 255 },
format: { with: VALID_EMAIL_REGEX },
uniqueness: { case_sensitive: false }
private
# Converts email to all lower-case.
def downcase_email
self.email = email.downcase
end
end
However in my teacher_test.rb test file, things get a little fuzzy. I try this
def setup
#user = users(:michael)
#user2 = users(:archer)
#user3 = users(:lana)
#user4 = users(:mallory)
#teacher = Teacher.new(name: "Phred Willard",
email: "pwillard#test.com",
phone: "1234567890",
user_id: [#user.id,
#user2.id,
#user3.id,
#user4.id])
end
test "should be valid" do
assert #uac.valid?
end
but that fails outright. Did I set my relationship up correctly? I obviously am not adding users correctly since the model fails a validity test. How would I add more users to that teacher? Thanks in advance.

Answer 1

I would like the teacher to have many users but each user to have only one teacher
You only need has_many / belongs_to...
#app/models/user.rb
class User < ActiveRecord::Base
belongs_to :teacher
end
#app/models/teacher.rb
class Teacher < ActiveRecord::Base
has_many :users
end
You'll need to add a teacher_id column in your users table (the opposite of what you have now):
class UpdateUsers < ActiveRecord::Migration
def change
change_table :users do |t|
t.references :teacher, index: true, foreign_key: true #-> teacher_id
end
end
end
--
The error you have is that you're calling user_id on teacher; it should be teacher_id on user:
#teacher = Teacher.new(name: "Phred Willard",
email: "pwillard#test.com",
phone: "1234567890",
user_ids: [#user.id,
#user2.id,
#user3.id,
#user4.id])
This should associate #teacher with the defined #users you've listed.
You'll also want to look at collection_singular_ids for the has_many association, which is why your test is failing.

Answer 2

Your teacher.rb should be
class Teacher < ActiveRecord::Base
has_many :users
before_save :downcase_email
validates :name, presence: true,
length: { maximum: 50 }
VALID_EMAIL_REGEX = /\A[\w+\-.]+#[a-z\d\-]+(\.[a-z\d\-]+)*\.[a-z]+\z/i
validates :email, presence: true,
length: { maximum: 255 },
format: { with: VALID_EMAIL_REGEX },
uniqueness: { case_sensitive: false }
private
# Converts email to all lower-case.
def downcase_email
self.email = email.downcase
end
end
and user.rb
class User < ActiveRecord::Base
belongs_to :teacher
# rest of your code here ....
end
You need teacher_id column in users table.