endpoint#present makes needless sql query

CHANGELOG.md

@@ -13,6 +13,7 @@ Next Release
 * [#614](https://github.com/intridea/grape/pull/614): Params with `nil` value are now refused by `RegexpValidator` - [@dm1try](https://github.com/dm1try).
 * [#494](https://github.com/intridea/grape/issues/494): Fixed performance issue with requests carrying a large payload - [@dblock](https://github.com/dblock).
 * [#619](https://github.com/intridea/grape/pull/619): Convert specs to RSpec 3 syntax with Transpec - [@danielspector](https://github.com/danielspector).
+* [#632](https://github.com/intridea/grape/pull/632): Usage of Grape::Endpoint#present for ActiveRecord relations doesn't make an additional query during entity's detection
 
 0.7.0 (4/2/2013)
 =================

lib/grape/endpoint.rb

@@ -336,14 +336,18 @@ def present(*args)
  entity_class = options.delete(:with)
 
  if entity_class.nil?
- # entity class not explicitely defined, auto-detect from first object in the collection
- object_instance = object.respond_to?(:first) ? object.first : object
+ # entity class not explicitely defined, auto-detect from relation#klass or first object in the collection
+ object_class = if object.respond_to?(:klass)
+ object.klass
+ else
+ object.respond_to?(:first) ? object.first.class : object.class
+ end
 
- object_instance.class.ancestors.each do |potential|
+ object_class.ancestors.each do |potential|
  entity_class ||= (settings[:representations] || {})[potential]
  end
 
- entity_class ||= object_instance.class.const_get(:Entity) if object_instance.class.const_defined?(:Entity) && object_instance.class.const_get(:Entity).respond_to?(:represent)
+ entity_class ||= object_class.const_get(:Entity) if object_class.const_defined?(:Entity) && object_class.const_get(:Entity).respond_to?(:represent)
  end
 
  root = options.delete(:root)

spec/grape/entity_spec.rb

@@ -121,6 +121,26 @@ def first
  get '/example'
  end
 
+ it 'does not use #first method on ActiveRecord::Relation to prevent needless sql query' do
+ entity = Class.new(Grape::Entity)
+ some_relation = Class.new
+ some_model = Class.new
+
+ allow(entity).to receive(:represent).and_return("Auto-detect!")
+ allow(some_relation).to receive(:first)
+ allow(some_relation).to receive(:klass).and_return(some_model)
+
+ some_model.const_set :Entity, entity
+
+ subject.get '/example' do
+ present some_relation
+ end
+
+ expect(some_relation).not_to receive(:first)
+ get '/example'
+ expect(last_response.body).to eq('Auto-detect!')
+ end
+
  it 'autodetection does not use Entity if it is not a presenter' do
  some_model = Class.new
  entity = Class.new