1 files changed, 30 insertions, 1 deletions
diff --git a/lib/gitlab/json_cache.rb b/lib/gitlab/json_cache.rb
index 1adf83739ad..e4bc437d787 100644
--- a/lib/gitlab/json_cache.rb
+++ b/lib/gitlab/json_cache.rb
@@ -71,7 +71,36 @@ module Gitlab
     end
 
     def parse_entry(raw, klass)
-      klass.new(raw) if valid_entry?(raw, klass)
+      return unless valid_entry?(raw, klass)
+      return klass.new(raw) unless klass.ancestors.include?(ActiveRecord::Base)
+
+      # When the cached value is a persisted instance of ActiveRecord::Base in
+      # some cases a relation can return an empty collection becauses scope.none!
+      # is being applied on ActiveRecord::Associations::CollectionAssociation#scope
+      # when the new_record? method incorrectly returns false.
+      #
+      # See https://gitlab.com/gitlab-org/gitlab-ee/issues/9903#note_145329964
+      klass
+        .allocate
+        .init_with(
+          "attributes" => attributes_for(klass, raw),
+          "new_record" => new_record?(raw, klass)
+        )
+    end
+
+    def attributes_for(klass, raw)
+      # We have models that leave out some fields from the JSON export for
+      # security reasons, e.g. models that include the CacheMarkdownField.
+      # The ActiveRecord::AttributeSet we build from raw does know about
+      # these columns so we need manually set them.
+      missing_attributes = (klass.columns.map(&:name) - raw.keys)
+      missing_attributes.each { |column| raw[column] = nil }
+
+      klass.attributes_builder.build_from_database(raw, {})
+    end
+
+    def new_record?(raw, klass)
+      raw.fetch(klass.primary_key, nil).blank?
     end
 
     def valid_entry?(raw, klass)