Create new item and place it into the Database - ruby-on-rails

Question

I am trying to create new object and to store it into the Database but I cannot understand why I am getting the following error: Here you can see the mistake:
Started POST "/cruises" for 127.0.0.1 at 2017-09-26 16:34:59 +0100
Processing by CruisesController#create as HTML
Parameters: {"utf8"=>"✓", "authenticity_token"=>"OkFmCPhl0pjFezWCsxp+c16wr3j9nbsdLIdgj+PsCMgSDmTzBoEJQ69tB8IA3uNayLRO+LMTi/73YqYCMImtCA==", "cruise"=>{"name"=>"NewAsasa", "ship_id"=>""}, "commit"=>"Create Cruise"}
(0.1ms) begin transaction
(0.1ms) rollback transaction
Rendering cruises/new.html.erb within layouts/application
Rendered cruises/_form.html.erb (3.6ms)
Rendered cruises/new.html.erb within layouts/application (4.4ms)
Completed 500 Internal Server Error in 12ms (ActiveRecord: 0.1ms)
ActionView::Template::Error (undefined method `map' for nil:NilClass
Did you mean? tap):
18:
19: <div class="field">
20: <em><%= f.label :ship_id %></em>
21: <%= f.collection_radio_buttons( :ship_id, #ships, :id, :name ) %>
22: </div>
23:
24: <div class="actions">
CruiseController - ""here you can see more about the controller below:I just need to write more text because it gives me error when I try to put this code, so do not read this explaination here it is for""
class CruisesController < ApplicationController
before_action :set_cruise, only: [:show, :edit, :update, :destroy]
rescue_from ActiveRecord::RecordNotFound, with: :redirect_if_not_found
# GET /cruises
# GET /cruises.json
def index
#cruises = Cruise.all
end
# GET /cruises/1
# GET /cruises/1.json
def show
end
# GET /cruises/new
def new
#cruise = Cruise.new
#ships = Ship.all
end
# GET /cruises/1/edit
def edit
#ships = Ship.all
end
# POST /cruises
# POST /cruises.json
def create
#cruise = Cruise.new(cruise_params)
respond_to do |format|
if #cruise.save
format.html { redirect_to #cruise, notice: 'Cruise was successfully created.' }
format.json { render :show, status: :created, location: #cruise }
else
format.html { render :new }
format.json { render json: #cruise.errors, status: :unprocessable_entity }
end
end
end
# PATCH/PUT /cruises/1
# PATCH/PUT /cruises/1.json
def update
respond_to do |format|
if #cruise.update(cruise_params)
format.html { redirect_to #cruise, notice: 'Cruise was successfully updated.' }
format.json { render :show, status: :ok, location: #cruise }
else
format.html { render :edit }
format.json { render json: #cruise.errors, status: :unprocessable_entity }
end
end
end
# DELETE /cruises/1
# DELETE /cruises/1.json
def destroy
#cruise.destroy
respond_to do |format|
format.html { redirect_to cruises_url, notice: 'Cruise was successfully destroyed.' }
format.json { head :no_content }
end
end
private
# Use callbacks to share common setup or constraints between actions.
def set_cruise
#cruise = Cruise.find(params[:id])
end
# Never trust parameters from the scary internet, only allow the white list through.
def cruise_params
params.require(:cruise).permit(:name, :ship_id)
end
end

Answer 1

Whatever you are iterating over in your controller is nil. Based on the code you have shown I am assuming it is #ships. I bet if you put puts #ships in your controller it will log nil.

Answer 2

Your save fails in the create action, (rollback transaction) so the if condition of the create action trigger the render :new.
However, it is a render, not a redirect, that mean the new action is not executed, and both #cruise and #ship does not exist (undefined).
Finally during the rendering of the new view, an error is triggered because #ships is undefined.
EDIT : I made an error, #ships is not nil it just does not exist (undefined).