Check if record does NOT exist in Rails (from array of ids)?

Question

I can do this to check if a record(s) exists (say id "1" exists, but "2" and "3" don't):

Model.exists?(:id => [1, 2, 3]) #=> true

How do I do the opposite, so:

Model.not_exists?(:id => [1, 2, 3]) #=> true

Answer 1

If you only need search records through ID you can try this

class Model
  def self.not_exists?(ids)
    self.find(ids)
    false
  rescue
    true
  end
end

If any of the IDs does not exist the find method will raise a ActiveRecord::RecordNotFound exception that we simply catch and return true.

Excuse my English :)

Answer 2

just add a ! operator

!Model.exists?(:id => [1, 2, 3]) #=> true

Answer 3

Use empty?, this is what you want. It uses count(*) vs select 1 as one.

> Rocketeer.where(:id => [1, 2, 3]).empty?
   (0.6ms)  SELECT COUNT(*) FROM "rocketeers" WHERE "rocketeers"."id" IN (1, 2, 3)
=> false

> Rocketeer.where(:id => [1, 2, 3]).any?
   (0.5ms)  SELECT COUNT(*) FROM "rocketeers" WHERE "rocketeers"."id" IN (1, 2, 3)
=> true

> Rocketeer.where(:id => [1, 2, 3]).exists?
  Rocketeer Exists (0.5ms)  SELECT  1 AS one FROM "rocketeers" WHERE "rocketeers"."id" IN (1, 2, 3) LIMIT 1
=> true

Answer 4

class Model
  def self.does_not_exist?(ids)
    Model.where(id: ids).count < ids.size
  end
end

Explanation: If (and only if) all the instances you're looking for exist, Model.where(id: ids).count is equal to ids.size.

However if there are one or more instances missing, the count will be lower, meaning that there's a record that does not exist.

Answer 5

A more Ruby-esque way of doing it would be to use unless with exists?. This way, you don't have to use !. I imagine your use case is something like this:

def my_method
    return unless Model.exists?(:id => [1, 2, 3])

    # do something
end

You can replace 1, 2, 3 with a variable (call it id or something) and even remove the array altogether if you'd like: .exists?(id: id)

Answer 6

Another simple way is to use the where method with an array of id's.

# If the count of the query is equal to the count of all of the id's then the statement will return false.
# Else it will return true if not all ids exists in the database.
Model.where(id: [1, 2, 3]).count < [1,2,3].count

Answer 7

To ensure all ids exist, not just one the following works without have to rescue

ids = [1,2,3]
Model.where(id: ids).count != ids.length

The exists? method will return true if any of the ids match. The above will ensure all ids exist.