How to simulate a NOT IN SQL condition in the following case

I'm using Ruby on Rails 2.3.8 and I would like to get all the @products that haven't been already added to the listed_products array.

For example, let's say I've got the following code:

listed_products = ['1', '2', '3', '4', '5']

#Then, I would like to do something like SELECT * FROM products where id not in
#(listed_products), and save the result in @products

I know the above SQL syntax won't work, but I just wanted to give you guys the idea of what I want to achieve.

Is开发者_StackOverflow中文版 there a "rails way" for doing this?

Thanks in advance!

Yes, you can do the following (Rails 2.3.x):

listed_products = [1,2,3,4,5]
Product.find(:all, :conditions => ["id NOT IN (?)", listed_products])

Or this in Rails 3.0.x:

listed_products = [1,2,3,4,5]
Product.where("id NOT IN (?)", listed_products)

Pan's answer is correct, but you can also use scopes in 2.3.8, which lets you chain with other scopes for the class:

class Product
    ...
    named_scope :excluding_ids, lambda { |*ids|
      if ids.count==0 then
        {}
      else
        {:conditions => ["id NOT IN (?)",ids]}
      end
    }
    ...
end

Then you can chain with other scopes in your class. Say you have a scope named :active. Then you can do:

Products.active.excluding_ids(*listed_products).find :all, ... more conditions ...

and it would be independent of order of the scopes:

Products.excluding_ids(*listed_products).active.find :all, ..

The best I can think of is:

SELECT * FROM products where id not = '1' and id not = '2' (etc...)

Not what you're after I'm sure, but it may be the only way!