How do I catch/solve an ActiveRecord:RecordInvalid exception caused when I save a built assocation

I am hoping to get some help solving a problem that I'm sure many of you could avoid in your sleep.

I have two models in a habtm relationship. A package can have many locations, and a location can have many packages. If my location model fails validation (due to an empty location address, for example), I get anActiveRecord:RecordInvalid exception. I understand that I'm getting this error because when I call package.save, rails automatically calls save! on the location association.

I'm not sure how to avoid the error or at least rescue the error. Do any of you have any good advice, both on how to solve the problem and on Rails best practices?

Here is the code:

def create
    @package = current_user.package.build(params[:package])
    package_location
    if @package.save
      flash[:success] = "Package created!"
      redirect_to root_path
    else        
      render 'pages/home'
    end
  end

  def package_location
    gps_processing if !session[:gps_aware]
    @package.locations.build(:address => session[:address])
  end

  def gps_processing
    session[:address] = [params[:story][:street_address], params[:story][:city], params[:story][:state], params[:story][:country]].compact.join(', ')
  end

class Package< ActiveRecord::Base

  belongs_to :user
  has_and_belongs_to_many :locations

  validates         :content,   :presence   => true, 
                    :length     => {:maximum => 140}
  validates      :user_id,    :presence => true

  default_scope :order => 'package.created_at DESC'

end

class Location < ActiveRecord::Base

  attr_accessible :lng, :lat, :address

  validates     :lng,       :presence   => true
  validates     :lat,       :presence   => true
  validates     :address,   :presence   => true

  geocoded_by :full_street_address, :latitude => :lat, :longit开发者_如何学JAVAude => :lng  

  before_validation :geocode

  has_and_belongs_to_many :packages

  def full_street_address
    address
  end
end

` Thanks in advance for your help!

The selected answer is not accurate. According to documentation here there's a simple way to catch rescue this exception:

begin
  complex_operation_that_calls_save!_internally
rescue ActiveRecord::RecordInvalid => invalid
  puts invalid.record.errors
end

You can access the messages instance variable of errors and get the field and error message associated.

A couple ideas off the top of my head:

Use @package.save! and a rescue block:

def create
  @package = current_user.package.build(params[:package])
  package_location
  @package.save!
  flash[:success] = "Package created!"
  redirect_to root_path
rescue      
  render 'pages/home'
end

Use validates_associated in your Package model, and only save if it's valid:

def create
  @package = current_user.package.build(params[:package])
  package_location

  # You might be able to just use if(@package.save), but I'm not positive.
  if(@package.valid?)
    @package.save!
    flash[:success] = "Package created!"
    redirect_to root_path
  else      
    render 'pages/home'
  end
end

And I'm sure there are a couple more ways, too, as you're working in Ruby...

Hope that helps!

Here's the code that I used to solve the problem while giving the user good feedback on the why the save failed. Please forgive my inelegant ruby code.

One small problem remains . . . if the package and the location both fail validation, only the location error message is displayed on reload. If the user then corrects the location error but not the package error, he is shown the package error message. I'm working on how to show all of the errors on the first reload

  def create
    @package= current_user.package.build(params[:package])
    if package_location && @package.save
        flash[:success] = "Package created!"
        redirect_to root_path
      else
        render 'pages/home'
    end
  end

 def package_location
   gps_processing if !session[:gps_aware]
   location = @package.locations.build(:address => session[:address])
   if !location.valid?
     @package.errors.add(:address, "You have entered an invalid address") 
     return false
   else
      return true
   end
 end

 def gps_processing
   session[:address] = [params[:story][:street_address], params[:story][:city], 
          params[:story][:state], params[:story][:country]].compact.join(', ')
 end