validating uniqueness within a has_many through - mysql

Question

I have a User that can have many Restaurants. I can also have multiple users.
I'd like to have it so that if User A creates Restaurant A, he should NOT be able to make another restaurant with the same name.
However, if User B goes to create Restaurant A, that should be allowed but still cannot make another Restaurant A afterwards.
I have the following has_many through relationship:
restaurant.rb
has_many :ownerships
has_many :users, :through => :ownerships
# This following ensures uniqueness of the name within the
# Restaurants table regardless of who the User is that created it.
validates :name, presence: true, uniqueness: true
user.rb
has_many :ownerships
has_many :restaurants, :through => :ownerships
ownership.rb
belongs_to :restaurant
belongs_to :user
What I've Tried
1. Adding :uniqu => true
I've tried adding :uniq => true to the restaurant.rb file so it looks like this:
has_many :ownerships
has_many :users, :through => :ownerships, :uniq => true
And removing uniqueness: true from the validation so it looks like this:
validates :name, presence: true
But that doesn't do anything useful.
2. Adding validation within ownership.rb
I've tried adding the validation to the ownership.rb file as such:
validates :restaurant, uniqueness: {:scope => :user}
But I get:
NoMethodError in RestaurantsController#create
undefined method `text?' for nil:NilClass
And I can't seem to tell it to look for the restaurant name within the scope of user either within this validation.
3. Creating before_create callback function
In my restaurant.rb file, I declared the following:
before_create :check_uniqueness
def check_uniqueness?
user = User.find_by_id(self.user_ids)
isUnique = false
user.restaurants.each do |restaurant|
if !Restaurant.find_by_name(self.name).nil? # Restaurant w/ same now found
isUnique = false
else
isUnique = true
end
return isUnique
end
end
My assumption is that before the restaurant record is created, it'll do this check_uniqueness check and if the function returns false, it'll not save.
But I'm getting the following error when I hit the submit button:
NameError in RestaurantsController#create
undefined local variable or method `check_uniqueness' for #<Restaurant:0x007f95a16d10f8>
Working Solution
Thanks to Robert Chuchro's help below, I was able to get the validation to work. Here's what I did:
restaurant.rb
before_create :unique_per_user?
def unique_per_user?
user = User.find_by_id(self.user_ids)
restaurant = user.restaurants.find(:all, :conditions => ["name = ?", self.name])
if restaurant.size > 0
self.errors.add(:name, ": You've already created a restaurant with this name.")
end
return (restaurant.size <= 0)
end

Answer 1

You can try to define a method to do this in your restaurant model
def unique_per_user?
#get user trying to create restaurant, either by paramter or association
#check if any of the user's current restaurant names match this name (return true/false)
end
now whereever you define a new restaurant check if its unique_per_user? before deciding to save it.