Re: Read-only attributes

Michael Klatt <mdklatt@ou.edu> writes:
> I have a table where one of the attributes is the time a row was inserted:
> 'updated TIMESTAMP DEFAULT CURRENT_TIMESTAMP'.

> Is there a way to define this attribute so that a user cannot override the
> default value?  I have tried this constraint, but it fails for any INSERT:
> 'updated ... CHECK (updated = CURRENT_TIMESTAMP)'.

No, but if you used a trigger rather than a default value, you could
force the field value to be always the time of insert.

You should, however, consider carefully whether that is *really* what
you want: there's no way to bypass a trigger.  Among other things,
dumping and reloading such a table would cause all the rows to acquire
the time of load.

A probably cleaner solution is not to give the untrusted users direct
write access on the table at all.  Give them write access on a view, and
let the INSERT rewrite rule for the view enforce the desired behavior.

            regards, tom lane