Editing params nested hash - ruby-on-rails

Question

Assume we have a rails params hash full of nested hashes and arrays. Is there a way to alter every string value (whether in nested hashes or arrays) which matches a certain criteria (e.g. regex) and still keep the output as a params hash (still containing nested hashes arrays?
I want to do some sort of string manipulation on some attributes before even assigning them to a model. Is there any better way to achieve this?
[UPDATE]
Let's say we want to select the strings that have an h in the beginning and replace it with a 'b'. so we have:
before:
{ a: "h343", b: { c: ["h2", "s21"] } }
after:
{ a: "b343", b: { c: ["b2", "s21"] } }
For some reasons I can't do this with model callbacks and stuff, so it should have be done before assigning to the respective attributes.

Answer 1

still keep the output as a params hash (still containing nested hashes arrays
Sure.
You'll have to manipulate the params hash, which is done in the controller.
Whilst I don't have lots of experience with this I just spent a bunch of time testing -- you can use a blend of the ActionController::Parameters class and then using gsub! -- like this:
#app/controllers/your_controller.rb
class YourController < ApplicationController
before_action :set_params, only: :create
def create
# Params are passed from the browser request
#model = Model.new params_hash
end
private
def params_hash
params.require(:x).permit(:y).each do |k,v|
v.gsub!(/[regex]/, 'string')
end
end
end
I tested this on one of our test apps, and it worked perfectly:
--
There are several important points.
Firstly, when you call a strong_params hash, params.permit creates a new hash out of the passed params. This means you can't just modify the passed params with params[:description] = etc. You have to do it to the permitted params.
Secondly, I could only get the .each block working with a bang-operator (gsub!), as this changes the value directly. I'd have to spend more time to work out how to do more elaborate changes.
--
Update
If you wanted to include nested hashes, you'd have to call another loop:
def params_hash
params.require(:x).permit(:y).each do |k,v|
if /_attributes/ ~= k
k.each do |deep_k, deep_v|
deep_v.gsub!(/[regex]/, 'string'
end
else
v.gsub!(/[regex]/, 'string')
end
end
end

Answer 2

In general you should not alter the original params hash. When you use strong parameters to whitelist the params you are actually creating a copy of the params - which can be modified if you really need to.
def whitelist_params
params.require(:foo).permit(:bar, :baz)
end
But if mapping the input to a model is too complex or you don't want to do it on the model layer you should consider using a service object.

Answer 3

Assuming you have a hash like this:
hash = { "hello" => { "hello" => "hello", "world" => { "hello" => "world", "world" => { "hello" => "world" } } }, "world" => "hello" }
Then add a function that transforms the "ello" part of all keys and values into "i" (meaning that "hello" and "yellow" will become "hi" and "yiw")
def transform_hash(hash, &block)
hash.inject({}){ |result, (key,value)|
value = value.is_a?(Hash) ? transform_hash(value, &block) : value.gsub(/ello/, 'i')
block.call(result, key.gsub(/ello/, 'i'), value)
result
}
end
Use the function like:
new_hash = transform_hash(hash) {|hash, key, value| hash[key] = value }
This will transform your hash and it's values regardless of the nesting level. However, the values should be strings (or another Hash) otherwise you'll get an error. to solve this problem just change the value.is_a?(Hash) conditional a bit.
NOTE that I strongly recommend you NOT to change the keys of the hash!