Question

I have a parameter hash that contains different variable and name pairs such as:

param_hash = {"system_used"=>"metric", "person_height_feet"=>"5"}

I also have an object CalculationValidator that is not an ActiveRecord but a ActiveModel::Validations. The Object validates different types of input from forms. Thus it does not have a specific set of variables.

I want to create an Object to validate it like this:

validator = CalculationValidator.new()
validator.system_used = "metric"
validator.person_height_feet = 5

validator.valid?

my problem right now is that I really would not prefer to code each CalculationValidator manually but rather use the information in the Hash. The information is all there so what I would like to do is something like this, where MAKE_INTO_VARIABLE() is the functionality I am looking for.

validator = CalculationValidator.new()
param_hash.each do |param_pair|
  ["validator.", param_pair[0]].join.MAKE_INTO_VARIABLE() = param_pair[1]
  # thus creating
  # "validator.system_used".MAKE_INTO_VARIABLE() = "metric"
  # while wanting: validator.system_used = "metric"
  # ...and in the next loop
  # "validator.person_height_feet".MAKE_INTO_VARIABLE() = 5
  # while wanting: validator.person_height_feet = 5
end

validator.valid?

Problem:
Basically my problem is, how do I make the string “validator.person_height” into the variable validator.person_height that I can use to store the number 5?

Additionally, it is very important that the values of param_pair[1] are stored as their real formats (integer, string etc) since they will be validated.

I have tried .send() and instance_variable_set but I am not sure if they will do the trick.

Answer 1

Something like this might work for you:

param_hash.each do |param, val|
  validator.instance_eval("def #{param}; @#{param} end")
  validator.instance_variable_set("@#{param}", val)
end

However, you might notice there’s no casting or anything here. You’d need to communicate what type of value each is somehow, as it can’t be assumed that “5” is supposed to be an integer, for example.

And of course I probably don’t have to mention, eval’ing input that comes in from a form isn’t exactly the safest thing in the world, so you’d have to think about how you want to handle this.