Ruby: create a parent only if at least 1 child exists - ruby-on-rails

Question

I have a parent - child relationship between Repairs & RepairItems.
A repair must have a least 1 RepairItem to be saved. I've made a nested (simple) form to create a Repair and display 3 blank repair_items.
I'm trying to work out how to make sure that a a Repair has at least 1 repair_item entered to allow the user to save the Repair. Otherwise I need to prompt the user that the repair can't be saved until at least 1 repair_item is entered..
Can anyone point me in the right direction for validation so that a user can't save a Repair without any Repair items entered? Thanks
class Repair < ActiveRecord::Base
attr_accessible :repair_id, :repairer_id, :fault_num, :vehicle_id, :date_reported, :date_closed, :hours_open, :mileage_open, :reported_to, :reported_by,
:repair_items_attributes
belongs_to :vehicle
belongs_to :repairer
has_many :repair_items, :dependent => :destroy
validates_presence_of :vehicle_id
validates_associated :repair_items
accepts_nested_attributes_for :repair_items, :reject_if => lambda { |a| a[:repair_type_id].blank? }, :allow_destroy => true
end
class RepairItem < ActiveRecord::Base
attr_accessible :repair_id, :problem, :solution, :repair_type_id, :priority, :repairer_id, :invoice, :cost, :tax,
:item_state_id, :mileage_closed, :hours_closed, :date_closed
belongs_to :repair
belongs_to :repairer
belongs_to :repair_type
belongs_to :item_state
#validates_presence_of :repair_id
validates_presence_of :repair_type_id
scope :open, where(:item_state_id => 1)
scope :monitor, where(:item_state_id=> 2)
scope :deferred, where(:item_state_id => 3)
scope :closed, where(:item_state_id => 4)
scope :cancelled, where(:item_state_id => 5)
end
class RepairsController < ApplicationController
before_filter :authorise
layout :resolve_layout
def index
#status = 1
#repairItems = RepairItem.open
end
def monitor
#status = 2
#repairItems = RepairItem.monitor
end
def deferred
#status = 3
#repairItems = RepairItem.deferred
end
def closed
#status = 4
#repairItems = RepairItem.closed
end
def cancelled
#status = 5
#repairItems = RepairItem.cancelled
end
def new
#repair = Repair.new
3.times { #repair.repair_items.build }
end
def create
# Instantiate a new object using form parameters
#repair = Repair.new(params[:repair])
# Save the object
if #repair.save
# If the save suceeds, redirect to the list action
redirect_to(repairs_path, :notice => 'Repair Created.')
else
# If the save fails, redisplay the form so user can fix problems
render :action => :new
end
end
<%= simple_form_for( #repair, :defaults => { :disabled => #current_user.read_only, :input_html => { :class => "span10" } }) do |f| %>
<fieldset>
<!-- This will display some text in red at the top of the form telling the user -->
<%= f.error_notification %>
<div class="st-row-fluid">
<div class="span2">
<%= f.association :vehicle, label_method: :fleet_num, value_method: :id, include_blank: true, label: 'Vehicle'%>
<p>Current Kms</p>
<p>Current Hours</p>
<p class="muted">Warranty Expires</p>
<p class="muted">Contract Maintenance</p>
</div>
<div class="span2">
<%= f.input :date_reported, :as => :date_picker, :input_html => { :class => "span10 st-datepicker"} %>
<%= f.input :mileage_open, :label => "Km/Miles" %>
<%= f.input :hours_open %>
</div>
<div class="span2">
<%= f.input :fault_num %>
<%= f.input :reported_to %>
<%= f.input :reported_by %>
</div>
</div>
<div class="row-fluid">
<h4> Items</h4>
<%= f.simple_fields_for :repair_items do |p| %>
<table class="table table-condensed">
<tr>
<%= render "repair_items", :p => p %>
</tr>
</table>
<% end %>
</div>
<%= f.error :base %>
<div class="st-form-actions">
<% if #current_user.read_only == false %>
<%= f.submit nil, :class => 'btn btn-success pull-right' %>
<% end %>
<%= link_to 'Cancel', repairs_path, :class => 'btn btn-danger pull-right' %>
</div>
</fieldset>
<% end %>
partial
<td><%= p.association :repair_type, label_method: :repair_type_label, value_method: :id, include_blank: true, label: 'Repair Type'%></td>
<td><%= p.input :problem %></td>
<td><%= p.input :solution %></td>
<td><%= p.input :priority %></td>
<td><%= p.association :repairer, label_method: :rep_name, value_method: :id, include_blank: true, label: 'Repairer'%></td>
</tr>
<tr>
<td><%= p.input :invoice %></td>
<td><%= p.input :cost %></td>
<td><%= p.input :tax %></td>
<td><%= p.input :date_closed, :as => :date_picker, :input_html => { :class => "span10 st-datepicker"} %></td>
<td><%= p.input :mileage_closed, :label => "Km/Miles" %></td>
<td><%= p.input :hours_closed %></td>
<td><%= p.association :item_state, label_method: :state_label, value_method: :id, label: 'Status', :default => 1 %></td>

Answer 1

Use validates_associated :repair_items in the repair to validate the repair items. The action has to construct the repair items using repair.RepairItem.build, so that the items will be associated with the repair, before attempting to save the repair. The repair is constructed before the repair items, but the repair_items will block the associated repair from saving.