matching POST route rails 4 - ruby-on-rails

Question

I am trying to upload a photo but after I press the upload button, I get this error. I am new to rails 4 so I'm not sure what I am missing.
My logic is when I click the submit button. This will cause the create action to fire and create a IncomePicture object and store it in my database.
No route matches [POST] "/income_pictures/new"
Routes:
root_path GET / static_pages#home
income_pictures_path GET /income_pictures(.:format) income_pictures#index
POST /income_pictures(.:format) income_pictures#create
new_income_picture_path GET /income_pictures/new(.:format) income_pictures#new
edit_income_picture_path GET /income_pictures/:id/edit(.:format) income_pictures#edit
income_picture_path GET /income_pictures/:id(.:format) income_pictures#show
PATCH /income_pictures/:id(.:format) income_pictures#update
PUT /income_pictures/:id(.:format) income_pictures#update
DELETE /income_pictures/:id(.:format) income_pictures#destroy
Controller:
class IncomePicturesController < ApplicationController
def new
#income_picture = IncomePicture.new
end
def create
#income_picture = IncomePicture.new(IncomePicture_params)
if #income_picture.save
flash[:notice] = "Income picture successfully uploaded"
redirect_to #income_picture
end
end
def show
#income_picture = IncomePicture.find(params[:id])
end
def index
#income_picture = IncomePicture.all
end
private
def IncomePicture_params
params.require(:income_picture).permit(:image, :name)
end
end
View:
<%= form_for :income_picture, :html => { :multipart => true } do |f| %>
<p>
<%= f.label :name %>
<%= f.text_field :name %>
</p>
<p>
<%= f.label :image %>
<%= f.file_field :image %>
</p>
<p><%= f.submit %></p>
<% end %>

Answer 1

I think you want form_for #income_picture rather than form_for :income_picture.
From the form guide: Using a symbol creates a form to new_income_picture_path, i.e. /income_picture/new whereas using a populated instance variable creates a form to income_pictures_path, i.e. income/pictures. Both set the form's method to POST. However, there's no such route as POSTing to /income_picture/new/, which is what caused the error.

Answer 2

form_for
To elaborate on the accepted answer, you have to remember that when calling form_for, Rails does some pretty amazing things:
It takes an ActiveRecord object and builds a "route" out of it (from the model)
It populates the form with the ActiveRecord object's data
It allows you to retain a perceived persistent state on the form (by perpetuating the data)
The problem you have is you're passing a simple symbol to the form - which prevents Rails from being able to accurately access the data required to make the 3 "magic" steps above possible.
This means you'll get random errors like the one you're seeing (IE in the absence of an ActiveRecord object, Rails will just use the same URL that you have on your page - /new)
--
ActiveRecord
The way to fix the issue you have is to replace the symbol with an ActiveRecord object, which was suggested in the accepted answer.
The reason why using an ActiveRecord object (#instance_variable) works is because of Ruby's core functionality -- it's a object orientated language. Being object orientated, it means that each time you populate an ActiveRecord object, you'll basically give Rails a series of other information, such as model_name etc.
This means when you pass the #instance_variable to the form_for method, Rails will be able to take the data from ActiveRecord & process it on screen for you