app/serializers/api/submission_file_serializer.rb
class Api::SubmissionFileSerializer < ActiveModel::Serializer
belongs_to :submission,
serializer: Api::SubmissionSerializer
attributes :id,
:submission_file_s3_key,
:aws_url
def aws_url
S3Service.new(object.submission_file_s3_key).expiring_url
end
end