Fix open issues: empty exports, N+1 queries, Turbolinks, plural routes

README.md

@@ -63,7 +63,7 @@ ATTRIBUTE_TYPES = {
 By default the gem adds the Export button to the partial `views/admin/application/_index_header.html.erb`. But if you have your own Administrate `index` views or override that partial in your application you can add the link manually:
 
 ```ruby
-link_to('Export', [:export, namespace.to_sym, page.resource_name.to_s.pluralize.to_sym, sanitized_order_params(page, :id).to_h.merge(format: :csv)], class: 'button') if existing_action?(resource_class, :export)
+link_to('Export', url_for(sanitized_order_params(page, :id).to_h.merge(action: :export, format: :csv)), class: 'button', target: '_blank', data: { turbolinks: false, turbo: false }) if existing_action?(resource_class, :export) && authorized_action?(resource_name, :export)
 ```
 
 Example:
@@ -82,13 +82,31 @@ Example:
 
     <%= link_to(
       'Export',
-      [:export, namespace.to_sym, page.resource_name.to_s.pluralize.to_sym, sanitized_order_params(page, :id).to_h.merge(format: :csv)],
-      class: 'button'
-    ) if existing_action?(resource_class, :export) %>
+      url_for(sanitized_order_params(page, :id).to_h.merge(action: :export, format: :csv)),
+      class: 'button',
+      target: '_blank',
+      data: { turbolinks: false, turbo: false }
+    ) if existing_action?(resource_class, :export) && authorized_action?(resource_name, :export) %>
   </div>
 ....
 ```
 
+The link uses `url_for(action: :export)` so it works regardless of the route name (e.g. models with plural names such as `UserSettings`, whose collection routes end in `_index`), and sets `data-turbolinks="false"`/`data-turbo="false"` so the CSV is downloaded instead of being rendered by Turbolinks/Turbo.
+
+### Associations and performance
+
+Associations (`Field::BelongsTo`, `Field::HasMany`, `Field::HasOne`, `Field::Polymorphic`, ...) that are exported are preloaded automatically to avoid N+1 queries. Associations excluded with `export: false` are not loaded.
+
+If your `transform_on_export` procs access nested associations, you can preload them by overriding `scoped_resource` in your controller:
+
+```ruby
+def scoped_resource
+  return super.preload(organizations: :address) if action_name == "export"
+
+  super
+end
+```
+
 ### Using with Pundit
 
 If you are using [Pundit](https://github.com/varvet/pundit) in your project you will receive an error saying `undefined method 'export?' for #<Admin::OrganizationPolicy>`. This is because the `export` action is not defined in the policy.

app/views/admin/application/_index_header.html.erb

@@ -27,9 +27,10 @@
 
     <%= link_to(
       'Export',
-      [:export, namespace, page.resource_name.to_s.pluralize.to_sym, sanitized_order_params(page, :id).to_h.merge(format: :csv)],
+      url_for(sanitized_order_params(page, :id).to_h.merge(action: :export, format: :csv)),
       class: 'button',
-      target: '_blank'
+      target: '_blank',
+      data: { turbolinks: false, turbo: false }
     ) if existing_action?(resource_class, :export) && authorized_action?(resource_name, :export) %>
   </div>
 </header>

lib/administrate_exportable/exporter_service.rb

@@ -7,7 +7,7 @@ def self.csv(dashboard, resource_class, resources)
     end
 
     def initialize(dashboard, resource_class, resources)
-      @dashboard = dashboard
+      @dashboard = dashboard.is_a?(Class) ? dashboard.new : dashboard
       @resource_class = resource_class
       @resources = resources
     end
@@ -40,7 +40,7 @@ def record_attribute(record, attribute_key, attribute_type)
       when Administrate::Field::BelongsTo.to_s, Administrate::Field::HasOne.to_s, Administrate::Field::Polymorphic.to_s
         field.display_associated_resource if field.data
       when Administrate::Field::HasMany.to_s
-        field.data&.count
+        field.data&.size
       when Administrate::Field::DateTime.to_s
         field.datetime if field.data
       when Administrate::Field::Date.to_s
@@ -72,15 +72,26 @@ def headers
     end
 
     def attributes_to_export
-      @attributes_to_export ||= dashboard.class::ATTRIBUTE_TYPES.select do |attribute_key, attribute_type|
+      @attributes_to_export ||= dashboard.attribute_types.select do |attribute_key, attribute_type|
         attribute_options = attribute_type.try(:options)
 
         !attribute_options || attribute_options[:export] != false
       end
     end
 
     def collection
-      resources
+      return resources if associations_to_preload.empty?
+
+      resources.preload(*associations_to_preload)
+    end
+
+    # Preload every exported association to avoid N+1 queries
+    def associations_to_preload
+      @associations_to_preload ||= attributes_to_export.select do |attribute_key, attribute_type|
+        attribute_type.respond_to?(:associative?) &&
+          attribute_type.associative? &&
+          resource_class.reflect_on_association(attribute_key)
+      end.keys
     end
   end
 end

spec/administrate_exportable/exporter_concern_spec.rb

@@ -14,5 +14,35 @@
 
       get export_admin_users_url(format: :csv)
     end
+
+    it "exports only records matching the search term" do
+      User.create(first_name: "John", last_name: "Doe", email: "john@email.com")
+      User.create(first_name: "Jane", last_name: "Roe", email: "jane@email.com")
+
+      get export_admin_users_url(format: :csv, search: "Jane")
+
+      rows = CSV.parse(response.body)
+      expect(rows.size).to eq 2
+      expect(rows[1][1]).to eq "Jane"
+    end
+
+    it "exports only headers when the search has no results" do
+      get export_admin_users_url(format: :csv, search: "nobody")
+
+      expect(response).to have_http_status(:ok)
+      expect(CSV.parse(response.body).size).to eq 1
+    end
+  end
+
+  describe "GET index" do
+    it "renders an export link that bypasses Turbolinks/Turbo" do
+      get admin_users_url(search: "John")
+
+      link = Nokogiri::HTML(response.body).at_css("a[href*='/admin/users/export.csv']")
+      expect(link).to be_present
+      expect(link["href"]).to include("search=John")
+      expect(link["data-turbolinks"]).to eq "false"
+      expect(link["data-turbo"]).to eq "false"
+    end
   end
 end

spec/administrate_exportable/exporter_service_spec.rb

@@ -108,5 +108,51 @@
         expect(parsed_data[1][4]).to eq "04:05AM"
       end
     end
+
+    context "when there are no records to export" do
+      let(:result) { AdministrateExportable::ExporterService.csv(UserDashboard.new, User, User.none) }
+
+      it "exports only the headers" do
+        expect(parsed_data.size).to eq 1
+        expect(parsed_data[0].first).to eq "Id"
+      end
+    end
+
+    context "when passing the dashboard class instead of an instance" do
+      let(:result) { AdministrateExportable::ExporterService.csv(UserDashboard, User, User.all) }
+
+      it "exports correct data" do
+        expect(parsed_data[1][1]).to eq "John"
+      end
+    end
+
+    context "preloading associations" do
+      before do
+        user = User.create(first_name: "Jane", last_name: "Roe", email: "jane@email.com", password: "1234567891011213")
+        user.dogs.create(name: "Rex")
+        user.create_cat(name: "Tom")
+      end
+
+      def count_queries(&block)
+        queries = []
+        callback = ->(*, payload) { queries << payload[:sql] unless payload[:name] == "SCHEMA" }
+        ActiveSupport::Notifications.subscribed(callback, "sql.active_record", &block)
+        queries.size
+      end
+
+      it "does not issue a query per record for exported associations" do
+        queries = count_queries { AdministrateExportable::ExporterService.csv(UserDashboard.new, User, User.all) }
+
+        # users + dogs + cats
+        expect(queries).to eq 3
+      end
+
+      it "preloads belongs_to associations" do
+        queries = count_queries { AdministrateExportable::ExporterService.csv(CatDashboard.new, Cat, Cat.all) }
+
+        # cats + users
+        expect(queries).to eq 2
+      end
+    end
   end
 end

spec/rails_helper.rb

@@ -13,3 +13,7 @@
 require "rspec/rails"
 require "administrate_exportable"
 require "spec_helper"
+
+RSpec.configure do |config|
+  config.use_transactional_fixtures = true
+end