Support for other types of association fields (#1176)

After merging thoughtbot/administrate#945, a problem surfaced with plugins that provide new types of association fields, such as https://github.com/pablobm/administrate-field-nested_has_many.

`Administrate::BaseDashboard` hard-codes the possible types of association fields in a list that is later used to determined the permitted params. This means that new types of fields cannot make permitted params and things break.

My proposed solution (see `lib/administrate/base_dashboard.rb`) does a programmatic search for field classes that inherit from `Administrate::Field::Associative`. This allows plugin authors not to worry about adding their new type to a list or any other sort of setup.

A potential problem with this approach is that it includes `Administrate::Field::Polymorphic` on the list. I don't know if this can cause problems down the line or not.

lib/administrate/base_dashboard.rb

@@ -59,8 +59,6 @@ def display_resource(resource)
     end
 
     def association_includes
-      association_classes = [Field::HasMany, Field::HasOne, Field::BelongsTo]
-
       collection_attributes.map do |key|
         field = self.class::ATTRIBUTE_TYPES[key]
 
@@ -74,5 +72,11 @@ def association_includes
     def attribute_not_found_message(attr)
       "Attribute #{attr} could not be found in #{self.class}::ATTRIBUTE_TYPES"
     end
+
+    def association_classes
+      @association_classes ||=
+        ObjectSpace.each_object(Class).
+          select { |klass| klass < Administrate::Field::Associative }
+    end
   end
 end

spec/example_app/app/dashboards/customer_dashboard.rb

@@ -1,4 +1,5 @@
 require "administrate/base_dashboard"
+require "administrate/field/has_many_variant"
 
 class CustomerDashboard < Administrate::BaseDashboard
   ATTRIBUTE_TYPES = {
@@ -8,7 +9,7 @@ class CustomerDashboard < Administrate::BaseDashboard
     lifetime_value: Field::Number.with_options(prefix: "$", decimals: 2),
     name: Field::String,
     orders: Field::HasMany.with_options(limit: 2, sort_by: :id),
-    log_entries: Field::HasMany.with_options(limit: 2, sort_by: :id),
+    log_entries: Field::HasManyVariant.with_options(limit: 2, sort_by: :id),
     updated_at: Field::DateTime,
     kind: Field::Select.with_options(collection: Customer::KINDS),
     country: Field::BelongsTo.with_options(

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

@@ -0,0 +1,13 @@
+<%#
+Just a copy of the HasMany _form partial, here to test that
+things won't break if the app adds new types of association fields
+%>
+
+<div class="field-unit__label">
+  <%= f.label field.attribute_key, field.attribute %>
+</div>
+<div class="field-unit__field">
+  <%= f.select(field.attribute_key, nil, {}, multiple: true) do %>
+    <%= options_for_select(field.associated_resource_options, field.selected_options) %>
+  <% end %>
+</div>

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

@@ -0,0 +1,6 @@
+<%#
+Just a copy of the HasMany _index partial, here to test that
+things won't break if the app adds new types of association fields
+%>
+
+<%= pluralize(field.data.size, field.attribute.to_s.humanize.downcase.singularize) %>

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

@@ -0,0 +1,23 @@
+<%#
+Just a copy of the HasMany _show partial, here to test that
+things won't break if the app adds new types of association fields
+%>
+
+<% if field.resources.any? %>
+  <% order = field.order_from_params(params.fetch(field.name, {})) %>
+  <% page_number = params.fetch(field.name, {}).fetch(:page, nil) %>
+  <%= render(
+    "collection",
+    collection_presenter: field.associated_collection(order),
+    collection_field_name: field.name,
+    page: page,
+    resources: field.resources(page_number, order),
+    table_title: field.name,
+  ) %>
+  <% if field.more_than_limit? %>
+    <%= paginate field.resources(page_number), param_name: "#{field.name}[page]" %>
+  <% end %>
+
+<% else %>
+  <%= t("administrate.fields.has_many.none", default: "–") %>
+<% end %>

spec/example_app/lib/administrate/field/has_many_variant.rb

@@ -0,0 +1,9 @@
+require "administrate/field/has_many"
+
+module Administrate
+  module Field
+    class HasManyVariant < HasMany
+      # Only here to test that this works out of the box
+    end
+  end
+end

spec/features/show_page_spec.rb

@@ -10,15 +10,15 @@
 
       visit admin_customer_path(customer)
 
-      within(".attribute-data--has-many table[aria-labelledby=orders]") do
+      within(table_for_attribute(:orders)) do
         ids_in_page1 = ids_in_table
         expect(ids_in_page1.count).to eq 2
         expect(order_ids).to include(*ids_in_page1)
       end
 
       click_on("Next ›")
 
-      within(".attribute-data--has-many table[aria-labelledby=orders]") do
+      within(table_for_attribute(:orders)) do
         ids_in_page2 = ids_in_table
         expect(ids_in_page2.count).to eq 2
         expect(order_ids).to include(*ids_in_page2)
@@ -73,15 +73,15 @@
 
     order_ids = orders.sort_by(&:id).map(&:id).reverse
 
-    within(".attribute-data--has-many table[aria-labelledby=orders]") do
+    within(table_for_attribute(:orders)) do
       expect(order_ids.first(2)).to eq(ids_in_table)
     end
 
     visit admin_customer_path(customer, orders: {
                                 order: :id, direction: :desc, page: 2
                               })
 
-    within(".attribute-data--has-many table[aria-labelledby=orders]") do
+    within(table_for_attribute(:orders)) do
       expect(order_ids.last(2)).to eq(ids_in_table)
     end
   end
@@ -104,11 +104,11 @@
     order_ids = orders.sort_by(&:id).map(&:id).reverse
     log_entry_ids = log_entries.sort_by(&:id).map(&:id)
 
-    within(".attribute-data--has-many table[aria-labelledby=orders]") do
+    within(table_for_attribute(:orders)) do
       expect(order_ids.first(2)).to eq(ids_in_table)
     end
 
-    within(".attribute-data--has-many table[aria-labelledby=log_entries]") do
+    within(table_for_attribute(:log_entries)) do
       expect(log_entry_ids.first(2)).to eq(ids_in_table)
     end
 
@@ -121,11 +121,11 @@
       },
     )
 
-    within(".attribute-data--has-many table[aria-labelledby=orders]") do
+    within(table_for_attribute(:orders)) do
       expect(order_ids.last(2)).to eq(ids_in_table)
     end
 
-    within(".attribute-data--has-many table[aria-labelledby=log_entries]") do
+    within(table_for_attribute(:log_entries)) do
       expect(log_entry_ids.first(2)).to eq(ids_in_table)
     end
   end
@@ -211,4 +211,8 @@
   def ids_in_table
     all("tr td:first-child").map(&:text).map(&:to_i)
   end
+
+  def table_for_attribute(attr_name)
+    find("table[aria-labelledby=#{attr_name}]")
+  end
 end