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.