Add Persistence.empty?

lib/active_model_persistence/persistence.rb

@@ -179,6 +179,21 @@ def count
 
       alias size count
 
+      # Returns true if there are no model objects saved in the object store
+      #
+      # @example
+      #   array_of_attributes = [
+      #   ]
+      #   ModelExample.create(array_of_attributes)
+      #   ModelExample.size #=> 0
+      #   ModelExample.empty? #=> true
+      #
+      # @return [Integer] the number of model objects in the object store
+      #
+      def empty?
+        object_array.size.zero?
+      end
+
       # Removes all model objects from the object store
       #
       # Each saved model object's `#destroy` method is called.

spec/active_model_persistence/persistence_spec.rb

@@ -387,6 +387,7 @@ def self.name
 
         it 'should have three object in the object store' do
           expect(model_class.size).to eq(3)
+          expect(model_class.empty?).to eq(false)
         end
 
         context 'after calling .destroy_all' do
@@ -396,6 +397,7 @@ def self.name
 
           it 'should remove all objects from the obejct store' do
             expect(model_class.size).to be_zero
+            expect(model_class.empty?).to eq(true)
           end
         end
       end