SQLite3 error in rails SQLite3::SQLException: no such column

Question

I am making a rails app where a user can post courses and also subscribe to courses.My model files are:
user.rb:

class User < ActiveRecord::Base
  has_many :courses, dependent: :destroy
  has_many :coursejoins, dependent: :destroy
  has_many :learnables, through: :coursejoins, class_name: "Course"
  has_many :comments, dependent: :destroy
  ...
end

course.rb:

class Course < ActiveRecord::Base
  belongs_to :user
  belongs_to :category
  has_many :coursejoins, dependent: :destroy
  has_many :students, through: :coursejoins, class_name: "User"
  has_many :documents, dependent: :destroy
  has_many :comments, dependent: :destroy
  ...
end

coursejoin.rb:

class Coursejoin < ActiveRecord::Base
  belongs_to :learnable, :class_name => "Course"
  belongs_to :student, :class_name => "User"
end

20160219171527_create_coursejoins.rb

class CreateCoursejoins < ActiveRecord::Migration
  def change
    create_table :coursejoins do |t|
      t.boolean :accepted
      t.timestamps
    end
  end
end

20160219174937_add_student_id_to_coursejoins.rb

class AddStudentIdToCoursejoins < ActiveRecord::Migration
  def change
    add_column :coursejoins, :student_id, :integer
  end
end

20160219224309_add_learnable_id_to_coursejoins.rb

class AddLearnableIdToCoursejoins < ActiveRecord::Migration
  def change
    add_column :coursejoins, :learnable_id, :integer
 end

end

The coursejoin model is like a relation between a course and a user.
When I try to do @course.students, i get error:

SELECT "users".* FROM "users" INNER JOIN "coursejoins" ON "users"."id" = "coursejoins"."student_id" WHERE "coursejoins"."course_id" = ?  [[nil, 1]]
ActiveRecord::StatementInvalid: SQLite3::SQLException: no such column: coursejoins.course_id: SELECT "users".* FROM "users" INNER JOIN "coursejoins" ON "users"."id" = "coursejoins"."student_id" WHERE "coursejoins"."course_id" = ?

I don't know SQL much so I am not able to decipher the error.
I looked at questions with similar error but none seemed related.
I have been stuck with this for two days.
How do I fix this?

Answer 1

Okay i got this solved and thought i should post the solution for future reference. Basically all that was needed to be done was adding

foreign_key: "learnable_id"

to

has_many :coursejoins, dependent: :destroy

in course model and

 foreign_key: "student_id"  

to

 has_many :coursejoins, dependent: :destroy  

to user model.