many methods to validate association model in rails

gistfile1.rb

# validation method 1

if @user.save && @order.save && @city.save
  ...
else
  ...
end

# validation method 2

if @user.valid? && @order.valid? && @city.valid?
  @user.save
  @order.save
  @city.save
  ...
else
  ...
end

# validation method 3

@city = City.new params[:city]
@user = User.new params[:user]
@user.city = @city
@order = Order.new params[:order]
@order.user = @user
unless [@user, @city, @order].map(&:valid?).include?(false)
  @user.save
  @city.save
  @order.save
  ...
else
  ...
end

# another version
if [@user, @city, @order].select{|model| model.valid? == false}.empty?
   ...
else
   ...
end  

# validation method 4

@city = City.new params[:city]
@user = @city.users.build params[:user]
@order = @user.orders.build params[:order]
@city.save ? redirect_to "/main/new" : render :action => "new"

# validation method 5
# define global AR Transaction filter
class TransactionFilter
  def filter(controller)
    return yield if controller.request.get?
    ActiveRecord::Base.transaction do
      yield
    end
  end
end

# define filter
around_filter :transaction_filter
def transaction_filter(&block)
  TransactionFilter.new.filter(self, &block)
end

# validation method 6

class Topic < ActiveRecord::Base
  attr_accessor :body
  has_many :posts,  :autosave => true 
  validates_presence_of :title
end
 
class Post < ActiveRecord::Base
  belongs_to :topic
  validates_presence_of :body
end
 
def create
  @topic = Topic.new(params[:topic])
  @topic.posts << Post.new(:body => params[:topic][:body])
  @topic.save ? redirect_to(@topic) : render :action => :new
end