added comments to import export reader class

lib/gitlab/import_export/import_export_reader.rb

@@ -11,6 +11,8 @@ module Gitlab
                                                                         methods: config_hash[:methods])
       end
 
+      # Outputs a hash in the format described here: http://api.rubyonrails.org/classes/ActiveModel/Serializers/JSON.html
+      # for outputting a project in JSON format, including its relations and sub relations.
       def project_tree
         @attributes_finder.find_included(:project).merge(include: build_hash(@tree))
       rescue => e
@@ -20,6 +22,9 @@ module Gitlab
 
       private
 
+      # Builds a hash in the format described here: http://api.rubyonrails.org/classes/ActiveModel/Serializers/JSON.html
+      #
+      # +model_list+ - List of models as a relation tree to be included in the generated JSON, from the _import_export.yml_ file
       def build_hash(model_list)
         model_list.map do |model_objects|
           if model_objects.is_a?(Hash)
@@ -30,6 +35,10 @@ module Gitlab
         end
       end
 
+      # Called when the model is actually a hash containing other relations (more models)
+      # Returns the config in the right format for calling +to_json+
+      # +model_object_hash+ - A model relationship such as:
+      #   {:merge_requests=>[:merge_request_diff, :notes]}
       def build_json_config_hash(model_object_hash)
         @json_config_hash = {}
 
@@ -44,6 +53,11 @@ module Gitlab
         @json_config_hash
       end
 
+
+      # If the model is a hash, process the sub_models, which could also be hashes
+      # If there is a list, add to an existing array, otherwise use hash syntax
+      # +current_key+ main model that will be a key in the hash
+      # +model_object+ model or list of models to include in the hash
       def process_sub_model(current_key, model_object)
         sub_model_json = build_json_config_hash(model_object).dup
         @json_config_hash.slice!(current_key)
@@ -55,6 +69,9 @@ module Gitlab
         end
       end
 
+      # Creates or adds to an existing hash an individual model or list
+      # +current_key+ main model that will be a key in the hash
+      # +model_object+ model or list of models to include in the hash
       def handle_model_object(current_key, model_object)
         if @json_config_hash[current_key]
           add_model_value(current_key, model_object)
@@ -63,6 +80,10 @@ module Gitlab
         end
       end
 
+      # Constructs a new hash that will hold the configuration for that particular object
+      # It may include exceptions or other attribute detail configuration, parsed by +@attributes_finder+
+      # +current_key+ main model that will be a key in the hash
+      # +value+ existing model to be included in the hash
       def create_model_value(current_key, value)
         parsed_hash = { include: value }
 
@@ -72,12 +93,20 @@ module Gitlab
         @json_config_hash[current_key] = parsed_hash
       end
 
+      # Adds new model configuration to an existing hash with key +current_key+
+      # It may include exceptions or other attribute detail configuration, parsed by +@attributes_finder+
+      # +current_key+ main model that will be a key in the hash
+      # +value+ existing model to be included in the hash
       def add_model_value(current_key, value)
         @attributes_finder.parse(value) { |hash| value = { value => hash } }
         old_values = @json_config_hash[current_key][:include]
         @json_config_hash[current_key][:include] = ([old_values] + [value]).compact.flatten
       end
 
+      # Construct a new hash or merge with an existing one a model configuration
+      # This is to fulfil +to_json+ requirements.
+      # +value+ existing model to be included in the hash
+      # +hash+ hash containing configuration generated mainly from +@attributes_finder+
       def hash_or_merge(value, hash)
         value.is_a?(Hash) ? value.merge(hash) : { value => hash }
       end