Include_blank in Belongs to form (#1222)

Replaces the functionality wherein nil is already included in the possible
options of belongs_to. In the current functionality of administrate, if you
add `include_blank: true` in f.select it would have double blank option in the
selections.

Changes in spec/factories.rb where made by running:

```
rubocop \
  --require rubocop-rspec \
  --only FactoryBot/AttributeDefinedStatically \
  --auto-correct
```

Co-authored-by: Bryan Mark Fajutag <bryan.fajutag@adish.co.jp>

app/views/fields/belongs_to/_form.html.erb

@@ -20,7 +20,7 @@ that displays all possible records to associate with.
   <%= f.label field.permitted_attribute %>
 </div>
 <div class="field-unit__field">
-  <%= f.select(field.permitted_attribute) do %>
-    <%= options_for_select(field.associated_resource_options, field.selected_option) %>
-  <% end %>
+  <%= f.select(field.permitted_attribute,
+               options_for_select(field.associated_resource_options, field.selected_option),
+               include_blank: field.include_blank_option) %>
 </div>

docs/customizing_dashboards.md

@@ -90,6 +90,9 @@ Example: `.with_options(scope: -> { MyModel.includes(:rel).limit(5) })`
 `:class_name` - Specifies the name of the associated class.
 Defaults to `:#{attribute}.to_s.singularize.camelcase`.
 
+`:include_blank` - Specifies if the select element to be rendered should include
+blank option. Default is `true`.
+
 `:searchable` - Specify if the attribute should be considered when searching.
 Default is `false`.
 

lib/administrate/field/belongs_to.rb

@@ -12,7 +12,7 @@ def permitted_attribute
       end
 
       def associated_resource_options
-        [nil] + candidate_resources.map do |resource|
+        candidate_resources.map do |resource|
           [display_candidate_resource(resource), resource.send(primary_key)]
         end
       end
@@ -21,6 +21,10 @@ def selected_option
         data && data.send(primary_key)
       end
 
+      def include_blank_option
+        options.fetch(:include_blank, true)
+      end
+
       private
 
       def candidate_resources

spec/example_app/app/dashboards/customer_dashboard.rb

@@ -18,6 +18,7 @@ class CustomerDashboard < Administrate::BaseDashboard
       class_name: "Country",
       searchable: true,
       searchable_fields: ["name"],
+      include_blank: true,
     ),
     password: Field::Password,
   }

spec/features/form_spec.rb

@@ -28,4 +28,38 @@
       expect(page).to have_label(custom_label)
     end
   end
+
+  context "include_blank option for belongs_to" do
+    before { create_list(:country, 5) }
+
+    it "should have blank option if set to true" do
+      dashboard = CustomerDashboard.new
+      fields = dashboard.attribute_types
+      territory = fields[:territory]
+      territory.options[:include_blank] = true
+
+      expect(territory.deferred_class).to eq(Administrate::Field::BelongsTo)
+      expect(territory.options[:include_blank]).to eq(true)
+
+      visit new_admin_customer_path
+      element_selections = find("select[name=\"customer[country_code]\"]")
+
+      expect(element_selections.first("option").value).to eq("")
+    end
+
+    it "should not have blank option if set to false" do
+      dashboard = CustomerDashboard.new
+      fields = dashboard.attribute_types
+      territory = fields[:territory]
+      territory.options[:include_blank] = false
+
+      expect(territory.deferred_class).to eq(Administrate::Field::BelongsTo)
+      expect(territory.options[:include_blank]).to eq(false)
+
+      visit new_admin_customer_path
+      element_selections = find("select[name=\"customer[country_code]\"]")
+
+      expect(element_selections.first("option").value).not_to eq("")
+    end
+  end
 end

spec/lib/fields/belongs_to_spec.rb

@@ -33,13 +33,39 @@
         candidates = field.associated_resource_options
 
         expect(Foo).to have_received(:all)
-        expect(candidates).to eq([nil])
+        expect(candidates).to eq([])
       ensure
         remove_constants :Foo
       end
     end
   end
 
+  describe "include_blank option" do
+    context "default value as true" do
+      it "determines if choices has blank option or not" do
+        association = Administrate::Field::BelongsTo
+        field = association.new(:customers, [], :edit)
+        candidates = field.associated_resource_options
+
+        expect(field.include_blank_option). to eq(true)
+        expect(candidates).to eq([])
+      end
+    end
+
+    context "set value as false" do
+      it "determines if choices has blank option or not" do
+        association = Administrate::Field::BelongsTo.with_options(
+          include_blank: false,
+        )
+        field = association.new(:customers, [], :edit)
+        candidates = field.associated_resource_options
+
+        expect(field.include_blank_option). to eq(false)
+        expect(candidates).to eq([])
+      end
+    end
+  end
+
   describe "primary_key option" do
     it "determines what primary key is used on the relationship for the form" do
       begin