Set timestamps on PostgreSQL INSERT and UPDATE.

[denispeplin]

This is not a "real" pull request, I don't expect it will be merged. It is just what I do to use this gem with Rails (I'm importing data from other application, which sends data without timestamps).
I tried other way: using now() as default for timestamp columns in database, but only INSERT can benefit from this approach, and UPDATE leaves updated_at untouched.

[evadne]

Hello @denispeplin

My solution to this is to use triggers instead of making Upsert depend on having timestamp columns. Some tables I use Upsert on do not have timestamp columns. You can create a couple trigger functions like these.

CREATE OR REPLACE FUNCTION public.bump_created_at()
RETURNS TRIGGER AS $$
BEGIN
  NEW.created_at = coalesce(NEW.created_at, now());
  NEW.updated_at = coalesce(NEW.updated_at, now());
  RETURN NEW;
END;
$$ language 'plpgsql';

CREATE OR REPLACE FUNCTION public.bump_updated_at()
RETURNS TRIGGER AS $$
BEGIN
  NEW.updated_at = coalesce(NEW.updated_at, now());
  RETURN NEW;   
END;
$$ language 'plpgsql';

Then for something like an objects table…

CREATE TRIGGER objects_updated_at
  BEFORE UPDATE ON objects
  FOR EACH ROW EXECUTE PROCEDURE
  bump_updated_at();

CREATE TRIGGER objects_created_at
  BEFORE INSERT ON objects
  FOR EACH ROW EXECUTE PROCEDURE
  bump_created_at();

Note that in Postgres, now() gives you time at start of transaction and statement_timestamp() gives you time at start of statement, so you may want to adjust accordingly.