Rails 4 - validate model is not working - ruby-on-rails

Question

Appreciate if you help me. I have a rails project, where people can book tickets to an airplanes (not a real project, just trying to learn rails :) ).
I have two cfaffolded objects - 'seats' and 'flights', and customer can buy a seat from every flight page (seats loads as partials).
My /app/views/flights/show.html.erb looks like that:
<p>
<strong>Departure:</strong>
<%= #flight.departure %>
</p>
<p>
<strong>Destination:</strong>
<%= #flight.destination %>
</p>
<p>
<strong>Baggage allowance:</strong>
<%= #flight.baggage_allowance %>
</p>
<%= render partial: "new_seat", locals: {seat: Seat.new(flight_id: #flight.id)} %>
<%= link_to 'Edit', edit_flight_path(#flight) %> |
<%= link_to 'Back', flights_path %>
My new_seat partial /app/views/flights/_new_seat.html.erb :
<h1>New Seat</h1>
<%= form_for(seat) do |f| %>
<% if seat.errors.any? %>
<div id="error_explanation">
<h2><%= pluralize(seat.errors.count, "error") %> prohibited this seat from being saved:</h2>
<ul>
<% seat.errors.full_messages.each do |message| %>
<li><%= message %></li>
<% end %>
</ul>
</div>
<% end %>
<%= f.hidden_field :flight_id %>
<div class="field">
<%= f.label :name %><br>
<%= f.text_field :name %>
</div>
<div class="field">
<%= f.label :baggage %><br>
<%= f.text_field :baggage %>
</div>
<div class="actions">
<%= f.submit %>
</div>
<% end %>
If it is important - I made new_seat partial by myself through copying it from /app/views/seats/new.html.erb
And now I need to validate baggage amount to prevent my clients grab big bags. I wrote my /app/models/seat.rb this way:
class Seat < ActiveRecord::Base
belongs_to :flight
def validate
if baggage > flight.baggage_allowance
seat.errors.add(:base, message: "You have too much baggage")
end
end
end
But it is not working - there is no errors on site when clients enters big amounts in baggage field. What am I doing wrong?

Answer 1

validate method is already available(its a class method that ActiveRecord provides us to implement our custom validations). You can use that method which AR provides. something like the code below
validate :check_baggage_limit
def check_baggage_limit
if baggage > self.flight.baggage_allowance
self.errors.add(:base, "You have too much baggage")
end
end

Answer 2

You can add your custom validations in two ways.
First is Custom method like below
class Seat < ActiveRecord::Base
belongs_to :flight
validate :baggage_limit
def baggage_limit
if baggage > flight.baggage_allowance
errors.add(:base, message: "You have too much baggage")
end
end
end
Second is Custom Validators
class BaggageValidator < ActiveModel::Validator
def validate(seat)
if seat.baggage > seat.flight.baggage_allowance
seat.errors.add(:base, message: "You have too much baggage")
end
end
end
class Seat < ActiveRecord::Base
include ActiveModel::Validations
belongs_to :flight
validates_with BaggageValidator
end
You must have misread the http://guides.rubyonrails.org/active_record_validations.html#custom-validators