CODEWITHSUNDEEP
ruby-on-railsruby-on-rails-3
Joe Essey
Joe Essey

Reputation: 3527

Rails - Use result of query as a conditional

I have a form that creates a new device based on the name of the device entered by the user, as well as some other data. I want to run a query on my Devices to see if the name they entered already exists so that they may not create a device with duplicate names. No matter how I set up a query to do the search, the method always states that the device already exists, even if it doesn't. With out the conditional statement, the code creates devices appropriately. Any ideas how I can work this out?

The method in Device controller:

def create
 if Device.where('name' => params[:name])
  respond_to do |format|
   format.html { redirect_to :back, notice: 'Cannot create device. It already exists.' }
  end
  else

 #Code that creates device

 #respond_to code

 end
end

Upvotes: 0

Views: 62

Answers (2)

Richard Brown
Richard Brown

Reputation: 11444

You should use model-level validation to prevent duplicate data.

class Device < ActiveRecord::Base
  validates_uniqueness_of :name, :message => 'already exists'

...
end

That way in your controller you can base decisions on the save method.

@device = params[:device]
respond_to do |format|
  if @device.save
    format.html # successful save
   else
    format.html { render action: 'new' }
   end
end

Upvotes: 1

Zippie
Zippie

Reputation: 6088

The reason why it always passes is because it returns a empty array and if [] will return true. To see if a user with that name exists you could use this:

Device.where(:name => params[:name]).exists?

but you shouldn't do it like that. You should use validations:

validates :name, :uniqueness => true

Check the guides for more insight about validations and how to use them: http://guides.rubyonrails.org/active_record_validations_callbacks.html

Also see the second answer for the more detailed explanation, and stuff like this is nicely explained in this book: http://ruby.railstutorial.org/chapters/modeling-users#sec-presence_validation

Upvotes: 1

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