Fix dependency proxy not working with object storage

Previously the dependency proxy controller would save the blob into
object storage, but the `file_store` column was never updated. As a
result, blobs could not be downloaded because it appeared to GitLab as
though the files never made it to object storage.

Just as we do with CI job artifacts, LFS files, and project exports, we
need to update this column after the CarrierWave-mounted file is saved.

Closes https://gitlab.com/gitlab-org/gitlab/-/issues/231563

changelogs/unreleased/sh-fix-dependency-proxy-object-storage.yml

+---
+title: Fix dependency proxy not working with object storage
+merge_request: 37878
+author:
+type: fixed

ee/app/models/dependency_proxy/blob.rb

@@ -9,6 +9,8 @@ class DependencyProxy::Blob < ApplicationRecord
 
   mount_uploader :file, DependencyProxy::FileUploader
 
+  after_save :update_file_store, if: :saved_change_to_file?
+
   def self.total_size
     sum(:size)
   end
@@ -16,4 +18,10 @@ class DependencyProxy::Blob < ApplicationRecord
   def self.find_or_build(file_name)
     find_or_initialize_by(file_name: file_name)
   end
+
+  def update_file_store
+    # The file.object_store is set during `uploader.store!`
+    # which happens after object is inserted/updated
+    self.update_column(:file_store, file.object_store)
+  end
 end

ee/spec/models/dependency_proxy/blob_spec.rb

@@ -36,4 +36,30 @@ RSpec.describe DependencyProxy::Blob, type: :model do
       expect(described_class.find_or_build(blob.file_name)).to eq(blob)
     end
   end
+
+  describe 'file is being stored' do
+    subject { create(:dependency_proxy_blob) }
+
+    context 'when existing object has local store' do
+      it 'is stored locally' do
+        expect(subject.file_store).to be(ObjectStorage::Store::LOCAL)
+        expect(subject.file).to be_file_storage
+        expect(subject.file.object_store).to eq(ObjectStorage::Store::LOCAL)
+      end
+    end
+
+    context 'when direct upload is enabled' do
+      before do
+        stub_dependency_proxy_object_storage(direct_upload: true)
+      end
+
+      context 'when file is stored' do
+        it 'is stored remotely' do
+          expect(subject.file_store).to eq(ObjectStorage::Store::REMOTE)
+          expect(subject.file).not_to be_file_storage
+          expect(subject.file.object_store).to eq(ObjectStorage::Store::REMOTE)
+        end
+      end
+    end
+  end
 end