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"}

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.

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

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.

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