FEATURE: A new site setting `public_user_custom_fields` which allows you

to whitelist custom fields that will be exposed to the Ember client
application.

app/models/concerns/has_custom_fields.rb

@@ -5,6 +5,31 @@ module HasCustomFields
   included do
     has_many :_custom_fields, dependent: :destroy, :class_name => "#{name}CustomField"
     after_save :save_custom_fields
+
+    # To avoid n+1 queries, we have this function to retrieve lots of custom fields in one
+    # go and create a "sideloaded" version for easy querying by id.
+    def self.custom_fields_for_ids(ids, whitelisted_fields)
+      klass = "#{name}CustomField".constantize
+      foreign_key = "#{name.underscore}_id".to_sym
+
+      result = {}
+
+      return result if whitelisted_fields.blank?
+      klass.where(foreign_key => ids, :name => whitelisted_fields).pluck(foreign_key, :name, :value).each do |cf|
+        result[cf[0]] ||= {}
+        unload_field(result[cf[0]], cf[1], cf[2])
+      end
+      result
+    end
+
+    def self.unload_field(target, key, value)
+      if target.has_key?(key)
+        target[key] = [target[key]] if !target[key].is_a? Array
+        target[key] << value
+      else
+        target[key] = value
+      end
+    end
   end
 
   def reload(options = nil)
@@ -32,14 +57,7 @@ module HasCustomFields
   def refresh_custom_fields_from_db
     target = Hash.new
     _custom_fields.pluck(:name,:value).each do |key, value|
-      if target.has_key? key
-        if !target[key].is_a? Array
-          target[key] = [target[key]]
-        end
-        target[key] << value
-      else
-        target[key] = value
-      end
+      self.class.unload_field(target, key, value)
     end
     @custom_fields_orig = target
     @custom_fields = @custom_fields_orig.dup
@@ -90,4 +108,4 @@ module HasCustomFields
       refresh_custom_fields_from_db
     end
   end
-end
+end

app/serializers/post_serializer.rb

@@ -48,8 +48,8 @@ class PostSerializer < BasicPostSerializer
              :user_deleted,
              :edit_reason,
              :can_view_edit_history,
-             :wiki
-
+             :wiki,
+             :user_custom_fields
 
   def moderator?
     !!(object.user && object.user.moderator?)
@@ -216,6 +216,16 @@ class PostSerializer < BasicPostSerializer
     scope.can_view_post_revisions?(object)
   end
 
+  def user_custom_fields
+    @topic_view.user_custom_fields[object.user_id]
+  end
+
+  def include_user_custom_fields?
+    return if @topic_view.blank?
+    custom_fields = @topic_view.user_custom_fields
+    custom_fields && custom_fields[object.user_id]
+  end
+
   private
 
   def post_actions

config/locales/server.en.yml

@@ -861,6 +861,7 @@ en:
 
     detect_custom_avatars: "Whether or not to check that users have uploaded custom avatars"
     max_daily_gravatar_crawls: "The maximum amount of times Discourse will check gravatar for custom avatars in a day"
+    public_user_custom_fields: "A whitelist of custom fields for a user that can be shown publically."
 
     allow_profile_backgrounds: "Allows users to upload profile backgrounds"
 

config/site_settings.yml

@@ -530,3 +530,7 @@ uncategorized:
     hidden: true
 
   notify_about_flags_after: 48
+
+  public_user_custom_fields:
+    list: true
+    default: ''

lib/topic_view.rb

@@ -7,7 +7,7 @@ require_dependency 'gaps'
 class TopicView
 
   attr_reader :topic, :posts, :guardian, :filtered_posts
-  attr_accessor :draft, :draft_key, :draft_sequence
+  attr_accessor :draft, :draft_key, :draft_sequence, :user_custom_fields
 
   def initialize(topic_id, user=nil, options={})
     @user = user
@@ -30,6 +30,10 @@ class TopicView
 
     filter_posts(options)
 
+    if SiteSetting.public_user_custom_fields.present? && @posts
+      @user_custom_fields = User.custom_fields_for_ids(@posts.map(&:user_id), SiteSetting.public_user_custom_fields.split('|'))
+    end
+
     @draft_key = @topic.draft_key
     @draft_sequence = DraftSequence.current(@user, @draft_key)
   end

spec/components/concern/has_custom_fields_spec.rb

@@ -152,5 +152,21 @@ describe HasCustomFields do
       test_item.custom_fields.should == {"jack" => "black", "bob" => "marley"}
       test_item2.custom_fields.should == {"sixto" => "rodriguez", "de" => "la playa"}
     end
+
+    it "supports bulk retrieval with a list of ids" do
+      item1 = CustomFieldsTestItem.new
+      item1.custom_fields = {"a" => ["b", "c", "d"], 'not_whitelisted' => 'secret'}
+      item1.save
+
+      item2 = CustomFieldsTestItem.new
+      item2.custom_fields = {"e" => 'hallo'}
+      item2.save
+
+      fields = CustomFieldsTestItem.custom_fields_for_ids([item1.id, item2.id], ['a', 'e'])
+      fields.should be_present
+      fields[item1.id]['a'].should =~ ['b', 'c', 'd']
+      fields[item1.id]['not_whitelisted'].should be_blank
+      fields[item2.id]['e'].should == 'hallo'
+    end
   end
 end