undefined method `id' for nil:NilClass (NoMethodError) - ruby-on-rails-4

Question

I encountered this error today, I search google for solution but I cannot find the correct answer for this. The error:
NoMethodError at /master/hotels/import
undefined method `id' for nil:NilClass
This is the templete file:
row
.col-xs-12
%p.pull-left
%button.btn.btn-white.btn-sm
一括削除
%p.pull-right
= link_to "新規作成", url_for(action: :new), class: "btn btn-white btn-sm"
= link_to "CSV Export", url_for(action: :index, format: 'csv'), class: "btn btn-white btn-sm"
= link_to "CSV Upload", url_for(action: :import), class: "btn btn-white btn-sm"
-#= form_tag url_for(action: :import), class: 'pull-right' do |f|
-#= file_field_tag :csv, as: :file
-#= submit_tag "CSV Upload", input_html: {class: "btn btn-white btn-sm"}
.col-xs-12
= render 'cruds/grid'
and here is my controller file:
class CrudsController < ApplicationController
before_action :load_crud
before_action :set_crud, only: [:show, :edit, :update, :destroy]
def load_crud
end
# GET /cruds
# GET /cruds.json
def index
#items_grid = initialize_grid(#model)
#csv = CSV.generate() do |csv|
csv << #model.column_names
#model.all.each do |item|
csv << item.attributes.values_at(*#model.column_names).map{|i| i.to_s.encode("cp932", "UTF-8")}
end
end
respond_to do |format|
format.html { render template: 'cruds/index'}
format.csv { send_data #csv }
#format.xls # {send_data #product.to_csv (col_sep: "|t")}
end
# render template: 'cruds/index'
end
# GET /cruds/1
# GET /cruds/1.json
def show
render template: 'cruds/show'
end
# GET /cruds/new
def new
#crud = #model.new
render template: 'cruds/new'
end
# GET /cruds/1/edit
def edit
render template: 'cruds/edit'
end
# POST /cruds
# POST /cruds.json
def create
#crud = #model.new(crud_params)
respond_to do |format|
if #crud.save
format.html { redirect_to [:master, #crud], notice: 'Crud was successfully created.' }
format.json { render action: 'show', status: :created, location: #crud }
else
format.html { render action: 'new' }
format.json { render json: #crud.errors, status: :unprocessable_entity }
end
end
end
# PATCH/PUT /cruds/1
# PATCH/PUT /cruds/1.json
def update
respond_to do |format|
if #crud.update(crud_params)
format.html { redirect_to [:master, #crud], notice: 'Crud was successfully updated.' }
format.json { head :no_content }
else
format.html { render action: 'edit' }
format.json { render json: #crud.errors, status: :unprocessable_entity }
end
end
end
# DELETE /cruds/1
# DELETE /cruds/1.json
def destroy
#crud.destroy
respond_to do |format|
format.html { redirect_to action: :index }
format.json { head :no_content }
end
end
def import
#model.import(params[:file])
redirect_to root_url, notice: "Products imported."
end
private
# Use callbacks to share common setup or constraints between actions.
def set_crud
#crud = #model.find_by_id(params[:id])
end
# Never trust parameters from the scary internet, only allow the white list through.
def crud_params
params[#hash].permit(#model.attribute_names)
end
end
I'm very confused about this error, can someone tell me any solution?

Answer 1

You're iterating over attribute names of #model, and reading them on #crud. #model has an attribute named id; #crud is nil. Either both should be same (probably), or in the somewhat unusual case that you do mean to read #model's attributes off of #crud, you need to check where #crud is assigned.

Answer 2

Your code is a bit confusing, some small comments:
model.find_by_id(params[:id])
Should be:
model.find(params[:id])
Next I would make sure that your view actually passes params[:id] to the view and not something like crud_id. If the latter is the case you should call this:
model.find_by(crud_id: params[:crud_id])
Lastly, I think you should add :file to your strong parameters.