Creating a record using has_many :through?

Question

I have the following models:

class Department < ApplicationRecord
  has_many :department_job_titles
  has_many :job_titles, through: :department_job_titles
end

class JobTitle < ApplicationRecord
  has_and_belongs_to_many :departments
end

class DepartmentJobTitle < ApplicationRecord
  belongs_to :department
  belongs_to :job_title
  validates :department_id, uniqueness: { scope: :job_title_id }
end

This is erring w PG::UndefinedColumn: ERROR: column department_job_titles.title does not exist LINE 1: ... "department_job_titles"."department_id" = $1 AND "departmen...

Department.first.department_job_titles.find_or_create_by(title: title)

DepartmentJobTitle has the following fields: id, department_id, job_title_id

What am I doing wrong here?

Answer 1

Try this:

job_title = JobTitle.find_or_create_by(title: title)
Department.first.job_titles << job_title unless job_title.in? Department.first.job_titles

Or that second line could be:

Department.first.job_titles = (Department.first.job_titles + [job_title]).uniq

Also:

class JobTitle < ApplicationRecord
  has_many :department_job_titles
  has_many :departments, through: :department_job_titles
end

... and ...

class DepartmentJobTitle < ApplicationRecord
  belongs_to :department
  belongs_to :job_title
  validates :department, presence: true, uniqueness: { scope: :job_title }
  validates :job_title, presence: true
end

... and think about what behaviour you want if someone destroys a JobTitle or Department -- either you want the DepartmentJobTitle destroyed also, or you want the destroy to be prevented, I expect.