Question

Consider this simple application in RUby on Rails:

Student & Teacher extends Person.
Person has 2 properties, name & age.
Student has 1 extra property, grade.
Teacher has 1 extra property, salary.

I want to store the student & teacher information in separate db tables. I want to take advantage of RoR’s utility class ActiveRecord:Base to retrive data for these models. Because Person is not expected to be instantiated, I can mix it with Student & Teacher as follows:

class Student < ActiveRecord:Base
include Person
end

module Person
end

Question:

1. Is this the correct way of implementation?
2. How to implement this without creating a databse table called persons? I only want to generate 2 tables, namely students and teachers, and both should have the 3 properties mentioned above.

Answer 1

Person does not have to be a model – it can be a library/module (which you then mixin as per your example). You’d keep that in RAILS_ROOT/lib.
Your Student and Teacher classes can be models (which use AR::Base), and the person can just be a bunch of common methods used by both.

Alternatively, if your child class is far more complicated – look into “Single table inheritance” – the description of which is beyond the scope of this answer… but you can google for it.