is it possible to have conditional default scope in rails?

Question

I am on rails 3.2.21, ruby version is 2.0

My requirement is to have role based conditional default scope for a particular model. eg

consider role variable as an attribute of logged in user

if role == 'xyz'
  default_scope where(is_active: false)
elsif role == 'abc'
   default_scope where(is_active: true)
end

It seems like very bad pattern. What about gems such as CanCan? — Aleksey, Sep 07 '16 at 06:59
Ruby on Rails reached its end of life-cycle with the release of [Rails 5.0](http://weblog.rubyonrails.org/2016/6/30/Rails-5-0-final/) on June 30th, 2016. Updating to a maintained version (4.2.x or 5.0.x at the moment) is highly recommended. — spickermann, Sep 07 '16 at 07:23

Andrey Deineko · Accepted Answer · 2016-09-07T07:17:15.743

2

Nothing is impossible in programming.

Using default_scope is a bad idea in general (lots of articles are written on the topic).

If you insist on using current user's atribute you can pass it as an argument to scope:

scope :based_on_role, lambda { |role|
  if role == 'xyz'
    where(is_active: false)
  elsif role == 'abc'
    where(is_active: true)
  end
}

And then use it as follows:

Model.based_on_role(current_user.role)

Sidenote: Rails 3.2.x - seriously?...

edited Sep 07 '16 at 07:17

answered Sep 07 '16 at 07:02

Andrey Deineko

Consider using `case role` over messy `if`s spaghetty. BTW, you have a typo in `elsif`. – Aleksei Matiushkin Sep 07 '16 at 07:12
@mudasobwa yep, thought about `case role`, but just copied what author had in OP. – Andrey Deineko Sep 07 '16 at 07:13
Also, dynamically evaluated `lambda` differs from static implementation by OP. – Aleksei Matiushkin Sep 07 '16 at 07:18
decided to use scope as Andrey suggested. yes on Rails 3.2.x, it is a legacy application, cost of migrating to newer version of Rails is high, but it is in pipeline. – srikant Sep 07 '16 at 18:00
@srikant please make sure to check the checkmark on the left near the answer if it answers your question – Andrey Deineko Oct 02 '16 at 07:03
1

Plus one for 'Nothing is impossible in programming.' I tell my clients this all the time. – Greg Blass Mar 15 '18 at 21:09

score 1 · Answer 2 · answered Sep 07 '16 at 07:13

1

default_scope where(
  case role
  when 'xyz' then { is_active: false }
  when 'abc' then { is_active: true }
  else '1 = 1'
  end
)

Also, please read the answer by Andrey Deineko, specifically the part about default scopes usage.

answered Sep 07 '16 at 07:13

I think it will just throw `undefined variable or method 'role' for Model` – Andrey Deineko Sep 07 '16 at 07:21
Once again, as I have said in the comment to your answer, there is a significant difference between static and dynamic clauses. This one is static, it’s evaluated in model’s context once. – Aleksei Matiushkin Sep 07 '16 at 07:26

2 Answers2