Support custom fields without corresponding model attributes

lib/administrate/page/base.rb

@@ -36,7 +36,7 @@ def attribute_field(dashboard, resource, attribute_name, page)
       end
 
       def get_attribute_value(resource, attribute_name)
-        resource.public_send(attribute_name)
+        resource.try(attribute_name)
       end
 
       attr_reader :dashboard, :options

spec/example_app/app/dashboards/customer_dashboard.rb

@@ -17,7 +17,8 @@ class CustomerDashboard < Administrate::BaseDashboard
       searchable_fields: ["name"],
       include_blank: true
     ),
-    password: Field::Password
+    password: Field::Password,
+    non_attribute_field: NonAttributeField
   }
 
   COLLECTION_ATTRIBUTES = ATTRIBUTE_TYPES.keys - %i[created_at updated_at]

spec/example_app/app/fields/non_attribute_field.rb

@@ -0,0 +1,5 @@
+class NonAttributeField < Administrate::Field::Base
+  def to_s
+    "Hello, Non Attribute Field"
+  end
+end

spec/example_app/app/views/fields/non_attribute_field/_form.html.erb

@@ -0,0 +1 @@
+<p>NonAttributeField is not supposed to be used in form.</p>

spec/example_app/app/views/fields/non_attribute_field/_index.html.erb

@@ -0,0 +1 @@
+<%= field.to_s %>

spec/example_app/app/views/fields/non_attribute_field/_show.html.erb

@@ -0,0 +1 @@
+<%= field.to_s %>

spec/features/show_page_spec.rb

@@ -277,6 +277,14 @@
     end
   end
 
+  it "displays non-attribute field" do
+    customer = create(:customer)
+
+    visit admin_customer_path(customer)
+
+    expect(page).to have_text("Hello, Non Attribute Field")
+  end
+
   def ids_in_table
     all("tr td:first-child").map(&:text).map(&:to_i)
   end