Rails: Two different NoMethodError's when trying to display files - ruby-on-rails

Question

I'm making a basic application and I made it so a user can attach a file to a form post. That all works perfectly fine, but now I'm trying to display a link to the file and it doesn't seem to work.
I'm getting two errors. One if I attach a file and another if I don't attach a file. They both say undefined method 'doc=' for nil:NilClass but are on different lines of code.
If I don't upload a file this is what I get: NoMethodError in Projects#index on this line of code <% if #project.doc %>.
If I do upload a file this is what I get: NoMethodError in ProjectsController#create on this line of code #project.doc = uploaded_io.original_filename
projects_controller.rb
class ProjectsController < ApplicationController
def index
#projects = Project.all
end
def show
end
def new
#projects = Project.new
end
def create #no view
#projects = Project.new(project_params)
uploaded_io = params[:doc]
if uploaded_io.present?
File.open(Rails.root.join('public', 'uploads', uploaded_io.original_filename), 'wb') do |file|
file.write(uploaded_io.read)
#project.doc = uploaded_io.original_filename
end
end
if #projects.save
redirect_to projects_path, :notice => "Your project was sent!"
else
render "new"
end
end
def edit
#projects = Project.find(params[:id])
end
def update #no view
#projects = Project.find(params[:id])
if #projects.update_attributes(project_params)
redirect_to projects_path, :notice => "Your project has been updated."
else
render "edit"
end
end
def destroy #no view
#projects = Project.find(params[:id])
#projects.destroy
redirect_to projects_path, :notice => "Your project has been deleted."
end
private
def project_params
params.require(:project).permit(:title, :description)
end
end
index.html.erb
<div class="container">
<div class="page-header">
<h1>Projects<small> Here are all of your projects.</small></h1>
</div>
</div>
<% #projects.each do |project| %>
<div class="container">
<div class="panel panel-default">
<div class="panel-heading">
<%= project.title %>
</div>
</div>
<div class="panel-body">
<p>
<%= project.description %>
</p>
<br>
<%= link_to "Discuss", new_project_discussion_path(project) %> |
<%= link_to "Tasks", new_project_task_path(project) %> |
<%= link_to "Edit", edit_project_path(project) %> |
<%= link_to "Delete", project, :method => :delete %>
<% if #project.doc %>
<p>Document: <%= link_to #project.doc, "/uploads/#{#project.doc}", :target => "_blank" %></p>
<% end %>
</div>
</div>
<%end%>
<br>
<br>
<div class="container">
<p><a class="btn btn-primary btn-lg" href="/projects/new" role="button">Create project</a></p>
</div>
_form.html.erb
<%= form_for(#projects, :html => { :multipart => true}) do |f| %>
<% if #projects.errors.any? %>
<ul>
<% #projects.errors.full_messages.each do |message| %>
<li><%= message %></li>
<% end %>
</ul>
<% end %>
<div class="container">
<div class="form-group">
<%= f.label :title %>
<%= f.text_field :title, class: "form-control" %>
</div>
<div class="form-group">
<%= f.label :description %>
<%= f.text_area :description, class: "form-control" %>
</div>
<%= label_tag :doc, 'Files (optional)' %>
<%= file_field_tag :doc %>
<br>
<div class="form-group">
<%= f.submit "Submit Project", class: "btn btn-primary" %>
</div>
<% end %>

Answer 1

Updated :
You have many errors, here are a few that I found :
uploaded_io = params[:doc]
Should be
uploaded_io = params[:project][:doc]
Also delete this line
#project.doc = uploaded_io.original_filename
You don't need that.
Finally, in your views, you should have project.doc instead of #project.doc