Ruby on Rails 4.0 - Retrieving a parameter from within a model - ruby-on-rails

Question

In my records index, I wish to insert an icon, of which name is calculated in the model, using parameters thanks to a parameters helper.
Retrieving parameters actually does not work.
In the BusinessRules index table, I specified an image tag:
<td><%= image_tag(business_rule.index_audit_tag, :alt => "Quality hit") %>
Which I extract from a public function in the model:
### display audit tag filename
def index_audit_tag
ratio = (1-self.bad_records / (self.all_records+1)) * 100
image_file = case ratio
when 0..60 then "red.png"
when 60..90 then "yellow-png"
# when red_threshold..yellow_threshold then red_image
# when yellow_threshold..green_threshold then yellow_image
else "green.png"
end
return image_file
end
It works fine when hard-coded, but I would like to use the red_threshold etc. parameters which are available through the parameters_helper:
def red_threshold
list_id = ParametersList.where("code=?", 'LIST_OF_DISPLAY_PARAMETERS').take!
#myparam = Parameter.where("parameters_list_id=? AND name=? AND ? BETWEEN active_from AND active_to", list_id, 'Tag 1-Green light', Time.now ).take!
#myparam.param_value.to_i
end
If I try using the parameters, I get the error:
undefined local variable or method `red_threshold'
How can I do that?

Answer 1

You can't call a helper method from within a model. Helpers are in the view layer of MVC and models are in thee model layer. To fix this you need to put both halves of the logic in the same layer.
If you want to keep index_audit_tag in the model layer:
In the Parameter model:
class Parameter
def self.red_threshold
list_id = ParametersList.where("code=?", 'LIST_OF_DISPLAY_PARAMETERS').take!
myparam = Parameter.where("parameters_list_id=? AND name=? AND ? BETWEEN active_from AND active_to", list_id, 'Tag 1-Green light', Time.now ).take!
myparam.param_value.to_i
end
end
(Note: You can probably improve this to do one query, but I'm not clear on your data model so I didn't try.)
And in your BusinessRule model:
def index_audit_tag
ratio = (1-self.bad_records / (self.all_records+1)) * 100
image_file = case ratio
when 0..60 then "red.png"
when 60..90 then "yellow-png"
when Parameter.red_threshold..Parameter.yellow_threshold then red_image
when Parameter.yellow_threshold..Parameter.green_threshold then yellow_image
else "green.png"
end
return image_file
end
If you want to put the icon logic in the view layer:
Many people would argue that the logic for choosing the right icon doesn't belong in the model. So another way to do this (and probably how I would do it) is to remove index_audit_tag from the model instead, and put it in a helper:
def index_audit_tag_for(business_rule)
ratio = (1-business_rule.bad_records / (business_rule.all_records+1)) * 100
image_file = case ratio
when 0..60 then "red.png"
when 60..90 then "yellow-png"
when red_threshold..yellow_threshold then red_image
when yellow_threshold..green_threshold then yellow_image
else "green.png"
end
return image_file
end
Then it will have no trouble finding the *_threshold methods which are also in the view.