Ruby how to modify parameters

Question

so i have this code that and my aim was to convert any empty string to null

def convert_empty_strings_to_null
  if request.patch? || request.post?
    convert_empty_strings_to_null_rec(request.params)
  end
end

def convert_empty_strings_to_null_rec(param)
  param = nil if param.empty? if param.is_a?(String)
  param.all?{|v| convert_empty_strings_to_null_rec v} if param.is_a?(Array)
  param.all?{|k,v| convert_empty_strings_to_null_rec v} if param.is_a?(Hash)
end

But i'm new to ruby on rails and i found it that it sends params by value and not by reference, so no change in params is made, how do i fix this ?

Note that all? does not replace anything. Use map instead. In case of the hash, use param.map{ |k,v| [x,y] }.to_h. — Raffael
– Raffael, Commented Jun 28, 2016 at 7:44

user2968505 · Accepted Answer · 2016-06-29 09:48:37Z

3

I assume that by "empty" you mean zero-with strings, meaning that strings consisting only of whitespace should be left intact. (Otherwise blank? and strip would be your friends.)

def convert_empty_strings_to_nil
  if request.patch? || request.post?
    request.params.each do |key, value| 
      request.params[key] = convert_empty_strings_to_nil_rec(value)
    end
  end
end

def convert_empty_strings_to_nil_rec(param)
  case param
  when String
    param.empty? ? nil : param
  when Array
    param.map{ |v| convert_empty_strings_to_nil_rec(v) }
  when Hash
    param.map{ |k,v| [k, convert_empty_strings_to_nil_rec(v)] }.to_h
  else
    param
  end
end

edited Jun 29, 2016 at 9:48

user2968505

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answered Jun 28, 2016 at 8:00

Raffael

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4 Comments

user2968505 Over a year ago

This would fix the problem but apparently the operator '=' isn't defined for params, is there a way to iterate over params and change the elements themselves without creating a new object?

Raffael Over a year ago

There are two ways: (1) Store the returned modified params hash in a new instance variable and use these. (2) Yes, knowing that request.params is always a hash, we can modify its values in-place. Should I elaborate?

user2968505 Over a year ago

Thanks i solved it by calling the recursive call on the first level of request.params for each value

Raffael Over a year ago

Cool! I updated the answer accordingly. Feel free to mark it as the accepted answer anytime :)

Harsh Trivedi · Accepted Answer · 2016-06-28 07:59:16Z

First of all, this is how your convert_empty_strings_to_null_rec method should be, for keeping the changes persistent:

def convert_empty_strings_to_null_rec(param)
      if param == ""
        updated_param == nil
      elsif param.is_a?(Array)
        updated_param == param.map{|x| nil if x.empty? }        
      elsif param.is_a?(Hash)
        updated_param = {}
        param.each do |k, v| 
            if v.empty?  
                updated_param[k] = nil
            else
                updated_param[k] = v
            end
        end
      end
      return updated_param
end

Further, I am assuming from your question that convert_empty_strings_to_null is a action method. It should be updated to catch what convert_empty_strings_to_null_rec method is returning.

def convert_empty_strings_to_null
  if request.patch? || request.post?
    updated_params = convert_empty_strings_to_null_rec(request.params)
  end
  # you can use the updated_params here on in this action method
end

Hope it helps : )

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