Rails ActiveRecord where clause - sql

Question

I want to select Cars from database with where clause looking for best DRY approach for my issue.
for example I have this two parameters
params[:car_model_id] (int)
params[:transmission_id] (int)
params[:from_date]
params[:to_date]
but I dont know which one will be null
if params[:car_model_id].nil? && !params[:transmission_id].nil?
if params[:from_date].nil? && params[:from_date].nil?
return Car.where(:transmission_id => params[:transmission_id])
else
return Car.where(:transmission_id => params[:transmission_id], :date => params[:from_date]..params[:to_date])
end
elseif !params[:car_model_id].nil? && params[:transmission_id].nil?
if params[:from_date].nil? && params[:from_date].nil?
return Car.where(:car_model_id=> params[:car_model_id])
else
return Car.where(:car_model_id=> params[:car_model_id], :date => params[:from_date]..params[:to_date])
end
else
return Car.where(:car_model_id=> params[:car_model_id], :transmission_id => params[:transmission_id], :date => params[:from_date]..params[:to_date])
end
what is best approach to avoid such bad code and check if parameter is nil inline(in where)

Answer 1

You can do:
car_params = params.slice(:car_model_id, :transmission_id).reject{|k, v| v.nil? }
and then:
Car.where(car_params)
Explanation: Since, you're checking if the particular key i.e.: :car_model_id and transmission_id exists in params. The above code would be something like this when you have just :transimission_id in params:
Car.where(:transmission_id => '1')
or this when you have :car_model_id in params:
Car.where(:car_model_id => '3')
or this when you'll have both:
Car.where(:transmission_id => '1', :car_model_id => '3')
NOTE: This will work only when you have params keys as the column names for which you're trying to run queries for. If you intend to have a different key in params which doesn't match with the column name then I'd suggest you change it's key to the column name in controller itself before slice.
UPDATE: Since, OP has edited his question and introduced more if.. else conditions now. One way to go about solving that and to always keep one thing in mind is to have your user_params correct values for which you want to run your queries on the model class, here it's Car. So, in this case:
car_params = params.slice(:car_model_id, :transmission_id).reject{|k, v| v.nil? }
if params[:from_date].present? && params[:from_date].present?
car_params.merge!(date: params[:from_date]..params[:to_date])
end
and then:
Car.where(car_params)

Answer 2

what is best approach to avoid such bad code and check if parameter is
nil inline(in where)
Good Question !
I will make implementation with two extra boolean variables (transmission_id_is_valid and
car_model_id_is_valid)
transmission_id_is_valid = params[:car_model_id].nil? && !params[:transmission_id].nil?
car_model_id_is_valid = !params[:car_model_id].nil? && params[:transmission_id].nil?
if transmission_id_is_valid
return Car.where(:transmission_id => params[:transmission_id])
elseif car_model_id_is_valid
return Car.where(:car_model_id=> params[:car_model_id])
....
end
I think now is more human readable.

Answer 3

First, I would change this code to Car model, and I think there is no need to check if params doesn't exists.
# using Rails 4 methods
class Car < ActiveRecord::Base
def self.find_by_transmission_id_or_model_id(trasmission_id, model_id)
if transmission_id
find_by trasmission_id: trasmission_id
elsif model_id
find_by model_id: model_id
end
end
end
In controller:
def action
car = Car.find_by_transmission_id_or_model_id params[:trasmission_id], params[:car_model_id]
end
edit:
This code is fine while you have only two parameters. For many conditional parameters, look at ransack gem.