Ruby on Rails: User helper method to read attribute - ruby-on-rails

Question

I'm trying to use a helper method to determine the value of an attribute for several records. Here is the basic function I am trying to get working (from the view):
<% if Baseline.where(subject_id: sub.subject_id).first.crf_status(crf) == 1 %>
<td bgcolor="#98FB98" >
<% else %>
My helper function is crf_status(crf), and it looks like this:
application_helper.rb
def crf_status(crf)
case crf
when Baseline then 'baseline_status'
when FollowUp3Week then 'follow_up_3_week'
...
end
end
So a working example would be if crf_status(Baseline) would return:
<% if Baseline.where(subject_id: sub.subject_id).first.baseline_status == 1 %>
<td bgcolor="#98FB98" >
<% else %>
Right now, the error is 'undefined method 'crf_status' for Baseline'. So based on what I've read, perhaps I have to reference ApplicationHelper in each controller? That doesn't sound right. Please let me know what you think.
Thanks.
edit. I forgot to make this more clear: crf_status(crf) is being passed an object from an array [Baseline, FollowUp3Week...].
The actual line starts with it as well -> if crf.where(subject_id:...

Answer 1

When you do method chaining like .first.crf_status(crf) you don't get a fresh global scope every time. I.e. to get this example to work your crf_status would need to be defined as an instance method on the Baseline model.
From a MVC design perspective, it's frowned upon to do database queries (i.e. where) from your views; you should do it from the controller instead. The choice to use helpers here is totally optional. By putting it in a helper all you're doing is making it inaccessible from code outside your views.
To cut to the chase, here's what you should write in your Baseline model file:
def crf_status(crf)
case crf
when Baseline then baseline_status
when FollowUp3Week then follow_up_3_week
end
end
Note that the baseline_status and follow_up_3_week are actually method calls with the implicit receiver self.

Answer 2

You are calling "crf_status" on an instance of a model, helpers can only be called on views and controllers.
You have to do something like this
<% if crf.where(subject_id: sub.subject_id).first.send(crf_status(crf)) == 1 %>
<td bgcolor="#98FB98" >
<% else %>
Anyway, that looks like a weird code smell (making queries on view is not right and that crf_status looks like something that you should move inside your models)

Answer 3

If you want to return a method that is to be called in the context, use the .send method.
Baseline.where(subject_id: sub.subject_id).first.send(crf_status(crf))
Whatever is returned from your method will be executed. This is a great metaprogramming example. You want to test against the class of the instance, so use the .class method on your case line. You'll want to return symbols not strings though, so do this:
def crf_status(crf)
case crf
when Baseline then :baseline_status
when FollowUp3Week then :follow_up_3_week
else :default
end
end
Edit: Changed case for type comparison