Do not validate the attachment file content type ...

when the attachment has not changed

app/models/concerns/attachable.rb

@@ -9,7 +9,7 @@ module Attachable
               presence: true,
               file_content_type: {
                 allow: ->(record) { record.accepted_content_types },
-                if: -> { association_class && attachment.attached? },
+                if: -> { association_class && attachment.attached? && attachment.new_record? },
                 message: ->(record, *) do
                   I18n.t("#{record.model_name.plural}.errors.messages.wrong_content_type",
                          content_type: record.attachment_content_type,

spec/models/attachable_spec.rb

@@ -58,4 +58,48 @@ describe Attachable do
       expect(document.valid?).to be(false)
     end
   end
+
+  context "file content types validation" do
+    it "is not applied when the image attachment has not changed" do
+      image = create(:image, :proposal_image)
+
+      expect(image.valid?).to be(true)
+
+      Setting["uploads.images.content_types"] = "image/gif"
+
+      expect(image.valid?).to be(true)
+    end
+
+    it "is applied when the image attachment changes" do
+      image = create(:image, :proposal_image)
+
+      expect(image.valid?).to be(true)
+
+      Setting["uploads.images.content_types"] = "image/gif"
+      image.attachment = Rack::Test::UploadedFile.new("spec/fixtures/files/clippy.png")
+
+      expect(image.valid?).to be(false)
+    end
+
+    it "is not applied when the document attachment has not changed" do
+      document = create(:document, :proposal_document)
+
+      expect(document.valid?).to be(true)
+
+      Setting["uploads.documents.content_types"] = "text/csv"
+
+      expect(document.valid?).to be(true)
+    end
+
+    it "is applied when the document attachment changes" do
+      document = create(:document, :proposal_document)
+
+      expect(document.valid?).to be(true)
+
+      Setting["uploads.documents.content_types"] = "text/csv"
+      document.attachment = Rack::Test::UploadedFile.new("spec/fixtures/files/clippy.pdf")
+
+      expect(document.valid?).to be(false)
+    end
+  end
 end