How to handle this type of model validation in Ruby on Rails
I have a controller / model presumably named Pets. Pets have the following declarations:
belongs_to :owner
has_many :dogs
has_many :cats
Not the best example, but again, it demonstrates what I'm trying to solve. Now when the request comes in as an HTTP POST on http://127.0.0.1/pets
, I want to instantiate Pets. The limitation here is that if the user doesn't submit at least one dog or one cat, this should result in a verification failure. He can have both, but he cannot be absent.
How do I handle this in Ruby on Rails? Dogs don't care if cats exist and vice versa. Can anyone show some example code for what the Pets model would look like to ensure that one or the other exists or doesn't work otherwise? Remember that dogs and cats are not attributes of the Pets model. I'm not sure how to avoid pets not being created if their resources for kids are not available.
errors.add also accepts an attribute, in this case there is no specific attribute that doesn't work. This is almost a "virtual" combination that is missing. Parameters can appear as cat_name = "bob" and dog_name = "stew", based on the attribute, I should be able to create a new cat or dog, but I need to know that at least one of them exists.
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You are looking for errors.add_to_base
. This should do the trick:
class Pet < ActiveRecord::Base
belongs_to :owner
has_many :dogs
has_many :cats
validate :has_cats_or_dogs
def has_cats_or_dogs
if dogs.empty? and cats.empty?
errors.add_to_base("At least one dog or cat required")
end
end
end
If you want to pass to cat_name
or dog_name
into a controller action, it might look like this:
class PetsController < ApplicationController
# ...
def create
@pet = Pet.new(params[:pet])
@pet.cats.build(:name => params[:cat_name]) if params[:cat_name]
@pet.dogs.build(:name => params[:dog_name]) if params[:dog_name]
if @pet.save
# success
else
# (validation) failure
end
end
end
Alternatively, for more flexibility, you can use nested attributes to create new cats and dogs in your controller.
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