Add ability to use nested only parameter

- The only string works much the same as before with its comma separation
-- Nested includes are indicated with square brackets "[ ]"
-- The nested include is the value immediately preceding the square brackets
-- The only string is the comma separated string inside those brackets
- Default includes are split between format types when necessary
-- This prevents unnecessary includes from being added on page load
- Available includes are those items which are allowed to be accessible to the user
-- Some aren't because they are sensitive, such as the creator of a flag
-- Some aren't because the number of associated items is too large
- The amount of times the same model can be included to prevent recursions
-- One exception is the root model may include the same model once
--- e.g. the user model can include the inviter which is also the user model
-- Another exception is if the include is a has_many association
--- e.g. artist urls can include the artist, and then artist urls again

app/controllers/dmails_controller.rb

@@ -15,7 +15,7 @@ class DmailsController < ApplicationController
   end
 
   def index
-    @dmails = Dmail.visible.paginated_search(params, defaults: { folder: "received" }, count_pages: true)
+    @dmails = Dmail.visible.paginated_search(params, defaults: { folder: "received" }, count_pages: true).includes(model_includes(params))
     respond_with(@dmails)
   end
 
@@ -51,6 +51,14 @@ class DmailsController < ApplicationController
 
   private
 
+  def default_includes(params)
+    if ["json", "xml"].include?(params[:format])
+      []
+    else
+      [:owner, :to, :from]
+    end
+  end
+
   def check_show_privilege(dmail)
     raise User::PrivilegeError unless dmail.visible_to?(CurrentUser.user, params[:key])
   end