#24082: Unique=True on TextField or CharField should not create an index
-------------------------------------+-------------------------------------
Reporter: djbug | Owner: nobody
Type: Bug | Status: new
Component: Database layer | Version: 1.7
(models, ORM) |
Severity: Normal | Resolution:
Keywords: | Triage Stage: Accepted
Has patch: 0 | Needs documentation: 0
Needs tests: 0 | Patch needs improvement: 0
Easy pickings: 0 | UI/UX: 0
-------------------------------------+-------------------------------------
Changes (by shaib):
* cc: shaib (added)
* stage: Unreviewed => Accepted
Comment:
First of all, +1 everything [comment:6 marfire] said.
Replying to [comment:5 djbug]:
> > Imposing uniqueness on text columns is almost always nonsense.
>
> For PostgreSQL, `CharField` maps to `varchar(n)` and `TextField` maps to
`text`. According to the official docs, there's no performance difference
between the two. Most DBA recommend `text` over `varchar(n)`
([http://stackoverflow.com/a/20334221/781695 Ref 1])
([http://blog.endpoint.com/2012/11/postgres-alter-column-problems-and.html
Ref 2]).
Well, I rephrase: s/text column/`TextField`/. `TextField`s are for big
blobs of text, not identifiers.
> That said, the above discussion about unique & index is true for
`CharField` too as far as Django is concerned.
>
> > the issue here really is whether `unique=True` implies
`db_index=True`. This holds for most field types, so I think most people
would expect it to hold for text fields as well.
>
> Could you explain why should `unique=True` imply creation of an index
explicitly ?
It generally does not. An index is created explicitly only to support
`LIKE` operations (as you noted, #12234).
>
> > You should get the behavior you expect, probably, with `unique=True,
db_index=False`. If this indeed gives you what you want, I'd resolve this
ticket by adding an admonition about this in the `TextField`
documentation.
>
> I've tried your suggestion. For a `TextFIeld`, the following two
generate the same constraint & index:
> {{{
> TextField( unique=True, db_index=False)
> }}}
> and
> {{{
> TextField( unique=True)
> }}}
>
I'm accepting based on this (and documentation should be added as well).
--
Ticket URL: <https://code.djangoproject.com/ticket/24082#comment:8>
Django <https://code.djangoproject.com/>
The Web framework for perfectionists with deadlines.
--
You received this message because you are subscribed to the Google Groups
"Django updates" group.
To unsubscribe from this group and stop receiving emails from it, send an email
to [email protected].
To post to this group, send email to [email protected].
To view this discussion on the web visit
https://groups.google.com/d/msgid/django-updates/063.ece921e0dd7620408bafe13b3effbc99%40djangoproject.com.
For more options, visit https://groups.google.com/d/optout.
