Hello,

I would like to ask, whether the following feature should/could be
part of Django.

There are cases that you would the database to handle certain fields.
For instance,

- set fields to their default value in the dabase-level (such as a
`created` timestamp),
- have the value of fields computed always by the database (e.g. with
a trigger),
- have virtual fields in the database etc.

The first case is especially important for timestamps, since setting
the default to `NOW()` will make sure (at least in postgres) that all
rows inserted under the same transaction will have the same timestamp
(compared to how auto_now_add works). This means that, when you insert
a lot of objects in one transaction, they will all have the exact same
timestamp. Moreover, relying on the database for setting default
values to fields reduces the amount of data that need to be sent to
the database server.

The second and third case allow to move some of the logic to the
database and take advantage of some features they offer as well as
speed up some things.

I understand there are alternatives at python-level, but I am not sure
how well they would work for high-traffic sites etc, without resorting
to raw queries for certain operations.

In order to achieve this (without resorting to hacks, like ignoring
the values that django sends in the database), django should ignore
these fields, when constructing an INSERT or UPDATE query. This could
be done by allowing a field to tell django to ignore it on INSERT or
UPDATE queries, the same way it does now for AutoFields.

You can find an implementation of this approach at
https://github.com/mpessas/django/commit/a663d8f95d9cca5112ccd33e3a303cae82908b60
and a demo project at https://github.com/mpessas/dbfield (timestamp
app).

So, does this sound like something that should be in core django? If
so, should I create a ticket in trac? Can anyone think of a better way
to achieve the same effect?

Regards,
Apostolis

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