CODEWITHSUNDEEP
rubyruby-on-rails-4
Drew H
Drew H

Reputation: 4739

Modify ruby hash in place( rails strong params)

This may be more a ruby question then rails question but I'm pretty sure I was able to do this in a vanilla ruby application.

I have strong params defined.

def trip_params
  params.require(:trip).permit(:name, :date)
end

Now I get those params in a controller method. I want to do this.

def save
  trip_params[:name] = 'Modifying name in place'
  #trip_params[:name] still equals original value passed
end

This never works. Name never changes. BTW: The type of trip_params is ActionController::Parameters

If I do a standard ruby script, it works.

test = {}    
test[:name] = "blah"    
test[:name] = "ok"    
puts test #{:name=>"ok"}

Upvotes: 51

Views: 40925

Answers (4)

Cruz Nunez
Cruz Nunez

Reputation: 3139

You could also do

def save
  data = trip_params.merge(name: 'new name')
  # use data later
end

If a new hash is merged into an old hash and if there are duplicate keys, the new hash's keys overwrite the old hash's matching keys.

Upvotes: 6

Иван Бишевац
Иван Бишевац

Reputation: 14641

If you really want to change params in controller you can do it on this way:

def save
  params[:trip][:name] = 'Modifying name in place'
  # Now trip_params[:name] is 'Modifying name in place'
end

Upvotes: 30

Bernardo Amorim
Bernardo Amorim

Reputation: 343

This is because there's no method such as trip_params[]=(arg, val).

I mean, when you call trip_params you are returning the value of params.require(:trip).permit(:name, :date), so every time you call trip_params you are getting the params again.

So, if I were you, I'd define the trip_params method as follow: 

def trip_params
  @trip_params ||= params.require(:trip).permit(:name, :date)
end

And would also define a method to change trip_params 

def trip_params[]= (key,val)
  trip_params # Ensure that trip_params is called once or you will get an error
  @trip_params[key] = val
end

So now when you call trip_params you would actually return @trip_params, and if @trip_params is not set yet it would set to params.require(:trip).permit(:name, :date)

And then when you call trip_params[:name] = "Some name" it will ensure first that @trip_params is initialized by calling trip_params and then it will set the :name param to"Some name"`

Hope I've helped you

Upvotes: 3

Nick Veys
Nick Veys

Reputation: 23939

permit returns a new hash with those keys in it, so you're not modifying the real params variable. You're also not saving a reference to the hash trip_params returns, so you get it fresh each call in save.

Try this:

def save
  tp = trip_params
  tp[:name] = 'Modifying name in place'
  # ... use tp later, it'll be in there
end

Or, if you really want it to be used the way you previously did, modify trip_params like so:

def trip_params
  @trip_params ||= params.require(:trip).permit(:name, :date)
end

Now that hash is lazily cached and the same one is returned on subsequent trip_params calls.

Upvotes: 73

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