Make array like classes configurable

README.md

@@ -69,6 +69,24 @@ This will result in JSON that looks something like this:
 ]
 ```
 
+
+You can also configure other classes to be treated like collections. For example, if you are using Mongoid, you can configure it to treat `Mongoid::Criteria` objects as collections:
+
+```ruby
+Blueprinter.configure do |config|
+  config.array_like_classes = [Mongoid::Criteria]
+end
+```
+
+Or if you wanted it to treat the `Set` class as a collection:
+
+```ruby
+Blueprinter.configure do |config|
+  config.array_like_classes = [Set]
+end
+```
+
+---
 </details>
 
 

lib/blueprinter/configuration.rb

@@ -2,7 +2,7 @@
 
 module Blueprinter
   class Configuration
-    attr_accessor :association_default, :datetime_format, :deprecations, :field_default, :generator, :if, :method, :sort_fields_by, :unless, :extractor_default, :default_transformers
+    attr_accessor :association_default, :datetime_format, :deprecations, :field_default, :generator, :if, :method, :sort_fields_by, :unless, :extractor_default, :default_transformers, :array_like_classes
 
     VALID_CALLABLES = %i(if unless).freeze
 
@@ -18,6 +18,7 @@ def initialize
       @unless = nil
       @extractor_default = AutoExtractor
       @default_transformers = []
+      @array_like_classes = []
     end
 
     def jsonify(blob)

lib/blueprinter/helpers/type_helpers.rb

@@ -3,13 +3,19 @@
 module Blueprinter
   module TypeHelpers
     private
-    def active_record_relation?(object)
-      !!(defined?(ActiveRecord::Relation) &&
-        object.is_a?(ActiveRecord::Relation))
+
+    def array_like_classes
+      [
+        Array,
+        defined?(ActiveRecord::Relation) && ActiveRecord::Relation,
+        *Blueprinter.configuration.array_like_classes
+      ].compact
     end
 
     def array_like?(object)
-      object.is_a?(Array) || active_record_relation?(object)
+      array_like_classes.any? do |klass|
+        object.is_a?(klass)
+      end
     end
   end
 end

spec/integrations/base_spec.rb

@@ -58,6 +58,29 @@
       end
     end
 
+    context 'Given passed object is array-like' do
+      let(:blueprint) { blueprint_with_block }
+      let(:additional_object) { OpenStruct.new(obj_hash.merge(id: 2)) }
+      let(:obj) { Set.new([object_with_attributes, additional_object]) }
+
+      context 'and is an instance of a configured array-like class' do
+        before do
+          Blueprinter.configure { |config| config.array_like_classes = [Set] }
+        end
+        after { reset_blueprinter_config! }
+
+        it 'should return the expected array of hashes' do
+          should eq('[{"id":1,"position_and_company":"Manager at Procore"},{"id":2,"position_and_company":"Manager at Procore"}]')
+        end
+      end
+
+      context 'and is not an instance of a configured array-like class' do
+        it 'should raise an error' do
+          expect { blueprint.render(obj) }.to raise_error(NoMethodError)
+        end
+      end
+    end
+
     context 'Inside Rails project' do
       include FactoryBot::Syntax::Methods
       let(:obj) { create(:user) }
@@ -383,6 +406,34 @@ def extract(association_name, object, _local_options, _options={})
           end
         end
       end
+
+      context 'Given passed object is an instance of a configured array-like class' do
+        let(:blueprint) do
+          Class.new(Blueprinter::Base) do
+            identifier :id
+            fields :make
+          end
+        end
+        let(:vehicle1) { build(:vehicle, id: 1) }
+        let(:vehicle2) { build(:vehicle, id: 2, make: 'Mediocre Car') }
+        let(:vehicle3) { build(:vehicle, id: 3, make: 'Terrible Car') }
+        let(:vehicles) { [vehicle1, vehicle2, vehicle3] }
+        let(:obj) { Set.new(vehicles) }
+        let(:result) do
+          vehicles_json = vehicles.map do |vehicle|
+            "{\"id\":#{vehicle.id},\"make\":\"#{vehicle.make}\"}"
+          end.join(',')
+          "[#{vehicles_json}]"
+        end
+
+        before do
+          Blueprinter.configure do |config|
+            config.array_like_classes = [Set]
+          end
+        end
+
+        it('returns the expected result') { should eq(result) }
+      end
     end
   end
   describe '::render_as_hash' do