Use the namespace for the active admin resource.

README.md

@@ -138,7 +138,7 @@ based on the input attribute name, you can pass an object with a
    end
 ```
 
-#### Mutlple Options Endpoints per Resource
+#### Multiple Options Endpoints per Resource
 
 A single ActiveAdmin resource can define multiple options endpoints:
 
@@ -167,6 +167,23 @@ To specify which collection to use, pass an object with a
    end
 ```
 
+#### Querying Multiple Attributes
+
+ActiveAdmin Searchable Select querying is performed by Ransack. As such, you can
+build your query in a way that it can query multiple attributes at once.
+
+```ruby
+   ActiveAdmin.register User do
+     searchable_select_options(scope: User.all,
+                               text_attribute: :username,
+                               filter: lambda do |term, scope|
+                                 scope.ransack(email_or_username_cont: term).result
+                               end)
+   end
+```
+
+In this example, the `all` scope will query `email OR username`.
+
 #### Passing Parameters
 
 You can pass additional parameters to the options endpoint:

lib/activeadmin/searchable_select/select_input_extension.rb

@@ -45,7 +45,7 @@ def collection_from_options
 
       def ajax_url
         return unless options[:ajax]
-        template.polymorphic_path([:admin, ajax_resource_class],
+        template.polymorphic_path([template.active_admin_namespace.name, ajax_resource_class],
                                   action: option_collection.collection_action_name,
                                   **ajax_params)
       end