ActiveRecord selection, modified by optional parameters

Question

I have an action method in my Rails controller which filters an ActiveRecord model depending on the submitted GET parameters.
Rubocop complains that Assignment Branch Condition Size is too high: 20.62/15.

Is there a way to improve the following code?

@measurements = Measurement.all
@measurements = @measurements.where(sensor_id: params[:sensor_id].split(',')) if params[:sensor_id].present?
@measurements = @measurements.last_per_sensor(params[:last_per_sensor]) if params[:last_per_sensor].present?
@measurements = @measurements.last(params[:last]) if params[:last].present?

Community · Accepted Answer · 2017-05-23 12:40:57Z

Some notes:

That's too much code for a controller method, it should be moved to the model.
The same name (@measurements) holds up to 4 different values. As a general rule, avoid variable rebinding: different values, different names.
More about how the filtering method could be written keeping it DRY: https://stackoverflow.com/a/4480285/188031

For example:

class Measurement < ActiveRecord::Base
  def self.filter(attributes)
    attributes.select { |k, v| v.present? }.reduce(all) do |scope, (key, value)|
      case key.to_sym
      when :sensor_id
        scope.where(key => value)
      when :last, :last_per_sensor 
        scope.send(key, value)
      else
        scope
      end 
    end
  end
end

And in the controller simply:

@measurements = Measurement.filter(params.slice(:sensor_id, :last, :last_per_sensor))

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