[MODEL] Perform partial updates in model where the ActiveModel support is available

When the model implements the `before_save` callback and the `changed_attributes` method,
intercept attribute changes, store them in the `@__changed_attributes` variable, and
perform a partial update (PUT .../_update) when updating the document in the index
in the `update_document` method

Fallback to full reindex via the `index_document` when changed attributes are not accessible.

Author: karmi

elasticsearch-model/lib/elasticsearch/model/indexing.rb

@@ -157,6 +157,21 @@ def settings(settings={}, &block)
       end
 
       module InstanceMethods
+
+        def self.included(base)
+          # Register callback for storing changed attributes for models
+          # which implement `before_save` and `changed_attributes` methods
+          #
+          # @note This is typically triggered only when the module would be
+          #       included in the model directly, not within the proxy.
+          #
+          base.before_save do |instance|
+            instance_variable_set(:@__changed_attributes,
+                                  Hash[ instance.changes.map { |key, value| [key, value.last] } ])
+            # puts "--- STORING changes --- (#{self.__elasticsearch__.instance_variable_get(:@__changed_attributes)})"
+          end if base.respond_to?(:before_save) && base.instance_methods.include?(:changed_attributes)
+        end
+
         def index_document(options={})
           document = self.as_indexed_json
 
@@ -177,9 +192,17 @@ def delete_document(options={})
         end
 
         def update_document(options={})
-          # TODO: Intercept changes to the record, and use `changed_attributes`
-          #       to perform update by partial doc.
-          index_document(options)
+          # puts "--- STORED changes --- (#{self.instance_variable_get(:@__changed_attributes)})"
+          if changed_attributes = self.instance_variable_get(:@__changed_attributes)
+            client.update(
+              { index: index_name,
+                type:  document_type,
+                id:    self.id,
+                body:  { doc: changed_attributes } }.merge(options)
+            )
+          else
+            index_document(options)
+          end
         end
       end
 

elasticsearch-model/lib/elasticsearch/model/proxy.rb

@@ -30,7 +30,10 @@ module Model
     module Proxy
 
       # Define the `__elasticsearch__` class and instance methods
-      # in including class.
+      # in including class and register the callback for intercepting changes in the model
+      #
+      # @note The callback is triggered only when `Elasticsearch::Model` is included in the
+      #       module and the functionality is accessible via the proxy.
       #
       def self.included(base)
         base.class_eval do
@@ -49,6 +52,15 @@ def __elasticsearch__ &block
             @__elasticsearch__.instance_eval(&block) if block_given?
             @__elasticsearch__
           end
+
+          # Register callback for storing changed attributes for models which implement
+          # `before_save` and `changed_attributes` methods (when `Elasticsearch::Model` is included)
+          #
+          before_save do |i|
+            i.__elasticsearch__.instance_variable_set(:@__changed_attributes,
+                                                      Hash[ i.changes.map { |key, value| [key, value.last] } ])
+            # puts "--- STORING changes --- (#{self.__elasticsearch__.instance_variable_get(:@__changed_attributes)})"
+          end if respond_to?(:before_save) && instance_methods.include?(:changed_attributes)
         end
       end