Rails：范围内的方法

Question

I have the following method on one of my models:

  def remaining_stock
    if initial_stock
      initial_stock - bought_items
    else
      0
    end
  end

In the controller, I'd like to pull all items owned by the user which have a remaining stock greater than zero. So, in short, something like

@remaining_items = Item.where(:user_id => current_user.id).{somehow specify that remaining stock > 0}

The method would be something along the lines of

def has_remaining_stock
  remaining_stock > 0
end

But I can't figure out how to add that to either the query itself, or some sort of scope which pulls in has_remaining_stock (I can scope with :conditions, but not other methods)

Any ideas appreciated.

Answer 1

The short answer is that you can't get what you want. Remember, you're generating SQL to be sent off to the database to fetch items. SQL doesn't include Ruby to run per row, but you can do other things with it. Something like:

.where("initial_stock = NULL or (initial_stock - bought_items) > 0")

should work. You could package that up as a scope on your model for cleaner semantics. You just need to express the function in an SQL condition.

Answer 2

我想您可以执行以下操作：

scope :has_remaining_stock, where("(initial_stock - bought_items) > 0)")