From 6331474abf72244042b4022368331e3ce5ce739a Mon Sep 17 00:00:00 2001
From: danhodge <dan@swipely.com>
Date: Mon, 14 Sep 2015 22:07:27 -0400
Subject: [PATCH] support dynamic attributes & merging collection values

Work in progress. Allows the parent attribute of a nested attribute
structure to be a dynamic attribute that is evaluated during
rendering. Adds a 'combine' option that can be used when exposing a
collection of items in a single presenter that controls how the
individual items are combined. No value maintains the existing behavior,
where each item is rendered as JSON and appended to the Array, while a
value of :merge results in each item's JSON representation being
Hash#merge'd into a single Hash.
---
 lib/grape_entity/entity.rb                    |  2 +-
 lib/grape_entity/exposure/base.rb             |  6 +++-
 lib/grape_entity/exposure/nesting_exposure.rb | 10 ++++++-
 spec/grape_entity/entity_spec.rb              | 28 +++++++++++++++++++
 4 files changed, 43 insertions(+), 3 deletions(-)

diff --git a/lib/grape_entity/entity.rb b/lib/grape_entity/entity.rb
index 89a0f1dd..07070d6c 100644
--- a/lib/grape_entity/entity.rb
+++ b/lib/grape_entity/entity.rb
@@ -498,7 +498,7 @@ def to_xml(options = {})
 
     # All supported options.
     OPTIONS = [
-      :rewrite, :as, :if, :unless, :using, :with, :proc, :documentation, :format_with, :safe, :attr_path, :if_extras, :unless_extras
+      :rewrite, :as, :if, :unless, :using, :with, :proc, :documentation, :format_with, :safe, :attr_path, :if_extras, :unless_extras, :combine
     ].to_set.freeze
 
     # Merges the given options with current block options.
diff --git a/lib/grape_entity/exposure/base.rb b/lib/grape_entity/exposure/base.rb
index c0c16199..27c75ac6 100644
--- a/lib/grape_entity/exposure/base.rb
+++ b/lib/grape_entity/exposure/base.rb
@@ -64,7 +64,11 @@ def serializable_value(entity, options)
           if partial_output.respond_to?(:serializable_hash)
             partial_output.serializable_hash(options)
           elsif partial_output.is_a?(Array) && partial_output.all? { |o| o.respond_to?(:serializable_hash) }
-            partial_output.map(&:serializable_hash)
+            if @options[:combine] == :merge
+              partial_output.reduce({}) { |memo, output| memo.merge(output.serializable_hash) }
+            else
+              partial_output.map(&:serializable_hash)
+            end
           elsif partial_output.is_a?(Hash)
             partial_output.each do |key, value|
               partial_output[key] = value.serializable_hash if value.respond_to?(:serializable_hash)
diff --git a/lib/grape_entity/exposure/nesting_exposure.rb b/lib/grape_entity/exposure/nesting_exposure.rb
index 4e2dfc49..01b7a8ab 100644
--- a/lib/grape_entity/exposure/nesting_exposure.rb
+++ b/lib/grape_entity/exposure/nesting_exposure.rb
@@ -57,7 +57,15 @@ def serializable_value(entity, options)
           normalized_exposures(entity, new_options).each_with_object({}) do |exposure, output|
             exposure.with_attr_path(entity, new_options) do
               result = exposure.serializable_value(entity, new_options)
-              output[exposure.key] = result
+
+              exposure_key = exposure.key.to_s
+              actual_key = if exposure_key.start_with?('__')
+                             entity.delegate_attribute(exposure_key[2..-1].to_sym)
+                           else
+                             exposure.key
+                           end
+
+              output[actual_key] = result
             end
           end
         end
diff --git a/spec/grape_entity/entity_spec.rb b/spec/grape_entity/entity_spec.rb
index 06229856..2102b44d 100644
--- a/spec/grape_entity/entity_spec.rb
+++ b/spec/grape_entity/entity_spec.rb
@@ -842,6 +842,34 @@ class Parent < Person
             expect(representation).to eq(id: nil, name: nil, user: { id: nil, name: nil, email: nil })
           end
         end
+
+        context 'dynamic attribute' do
+          it 'determines the attribute value during representation' do
+            element_entity = Class.new(Grape::Entity)
+            element_entity.expose(:__date) do
+              element_entity.expose :fname, as: :first_name
+              element_entity.expose :last_name
+            end
+
+            collection_entity = Class.new(Grape::Entity)
+            collection_entity.present_collection(true)
+            collection_entity.expose(:items, using: element_entity, combine: :merge)
+
+            values = [
+              OpenStruct.new(date: '2015-09-01', fname: 'First', last_name: 'L.'),
+              OpenStruct.new(date: '2015-08-01', fname: 'F.', last_name: 'Last')
+            ]
+
+            serialized = collection_entity.represent(values).serializable_hash
+
+            expect(
+              serialized[:items]
+            ).to eq({
+                      '2015-09-01' => { first_name: 'First', last_name: 'L.' },
+                      '2015-08-01' => { first_name: 'F.', last_name: 'Last' }
+                    })
+          end
+        end
       end
     end