param is missing or the value is empty: ph - rails - ruby-on-rails

Question

This is a possible duplicate, but I have read and tried nearly all suggestions, but I keep getting the error on the New action view. I am using Rails 5.
I have tried the following:
private
def ph_params
params.require(:ph).permit(:amount)
end
And also tried the following, and the error disappeared, but my values were not saving to database, only shows Nil:
private
def ph_params
params.permit(:amount)
end
My controller:
class PhsController < ApplicationController
def index
end
def new
#ph = Ph.new(ph_params)
end
def create
#ph = Ph.new(ph_params)
respond_to do |format|
if #ph.save
format.html { redirect_to #ph }
else
format.html { render "new" }
end
end
end
def show
#ph = Ph.find(params[:id])
end
private
def ph_params
params.require(:ph).permit(:amount)
end
end
new.html.erb form start
<%= simple_form_for #ph, url: phs_path do |f| %>
Model
class Ph < ApplicationRecord
end
I might be missing something. Your assistance is appreciated, thank you in advance.

Answer 1

Modify your new action to
def new
#ph = Ph.new
end
The reason you're getting the error is because when you hit the route phs/new, no key ph is passed in the params hash to the controller but you're trying to access params[:ph][:amount] which is the return value of ph_params. This is why the error 'param is missing or the value is empty' occurs.
If you want to know what values were passed in the params has for every request, add the following line to your application.html.erb
<%= params.inspect %>
You'll probably find a hash with two keys {"controller" => "phs", "action" => "new"} in the new page.
However, when you try to create a new ph object, you will find a key ph in your params hash.
By the way, I think you don't quite understand strong parameters. I would suggest you to read http://api.rubyonrails.org/classes/ActionController/StrongParameters.html