Prefill new resource from params in the new action

app/controllers/administrate/application_controller.rb

@@ -33,7 +33,7 @@ def show
     end
 
     def new
-      @resource = resource = new_resource.tap do |resource|
+      @resource = resource = new_resource(new_resource_params).tap do |resource|
         authorize_resource(resource)
       end
 
@@ -217,6 +217,14 @@ def apply_collection_includes(relation)
       relation.includes(*resource_includes)
     end
 
+    def new_resource_params
+      if params.key?(resource_class.model_name.param_key)
+        resource_params
+      else
+        {}
+      end
+    end
+
     def resource_params
       params.require(resource_class.model_name.param_key)
         .permit(dashboard.permitted_attributes(action_name))

spec/controllers/admin/blog/posts_controller_spec.rb

@@ -44,6 +44,14 @@
 
       expect(locals[:page]).to be_instance_of(Administrate::Page::Form)
     end
+
+    it "prefills the new namespaced resource from params" do
+      locals = capture_view_locals do
+        get :new, params: {blog_post: {title: "Hello"}}
+      end
+
+      expect(locals[:page].resource.title).to eq("Hello")
+    end
   end
 
   describe "GET edit" do

spec/controllers/admin/customers_controller_spec.rb

@@ -104,6 +104,24 @@ def default_sorting_direction
 
       expect(locals[:page]).to be_instance_of(Administrate::Page::Form)
     end
+
+    it "builds a new resource without params" do
+      locals = capture_view_locals { get :new }
+
+      expect(locals[:page].resource).to be_a_new(Customer)
+      expect(locals[:page].resource.name).to be_nil
+    end
+
+    it "prefills the new resource from params" do
+      locals = capture_view_locals do
+        get :new, params: {customer: {name: "Bob", email: "bob@example.com"}}
+      end
+
+      resource = locals[:page].resource
+      expect(resource).to be_a_new(Customer)
+      expect(resource.name).to eq("Bob")
+      expect(resource.email).to eq("bob@example.com")
+    end
   end
 
   describe "GET edit" do