PostgreSQL Partial Indexes package

[Mattias Linnap]

Hi django-developers,

I have written a package that implements PostgreSQL and SQLite partial indexes on top of the new class-based indexes: https://github.com/mattiaslinnap/django-partial-index

The most common use case is partial unique constraints, but I have a few projects where non-unique partial indexes have turned out useful as well.

I have a few questions on how to continue with this:

1. Right now the "where condition" expression is provided as a string, and has to be different for PostgreSQL and SQLite in some common cases (for example boolean literals). Is there a good abstraction for SQL expressions somewhere in Django internals that I could use instead, something similar to Q-expressions perhaps? In particular, to add validate_unique() support to ModelForms, I would need to be able to extract all fields that are mentioned in the where condition.

2. I've seen mentions of a "check constraints" support being in development (https://github.com/django/django/pull/7615). Will that include partial unique constraints, or is just for the per-column checks?

3. If separate, then it would be nice to one day get partial indexes merged into the contrib.postgres package. Do you have any suggestions on what needs to happen before that - more test coverage, more contributors, more users, or similar?

Best,

Mattias

[Tim Allen]

I would love to see partial indexes supported. Great work! As far as databases with Django support:

- PostgreSQL supports partial indexes

- SQLite supports partial indexes

- SQL Server supports them, called "filtered indexes"

- Oracle: Sort of supports them: https://blog.jooq.org/2017/01/18/how-to-emulate-partial-indexes-in-oracle/

- MySQL/Maria/Drizzle: no support, AFAIK.

Would we want to build partial indexes in for all databases, with the caveat that they would be ignored on MySQL and perhaps Oracle? In those cases, would be default to a full index?

Regards,

Tim

[Adam Johnson]

It looks to me that the same trick on Oracle can be used on MySQL/MariaDB - indexing a generated column. There's a comment on https://mariadb.com/kb/en/library/generated-columns/ to that effect.

P.S. Drizzle is long dead, the site isn't even up any more :)

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[Ashley Waite]

I did a similar thing (but only tested in postgres) a while back, using Q's / filter clause to generate the where clause.

Perhaps with our powers combined we're close to a generalised implementation?

https://github.com/ashleywaite/django-more/blob/master/django_more/indexes.py

[Sergey Fursov]

Hi everyone,

In our company, we also use the ability to define our own indexes, but with the current implementation of base Index class, we basically need to copy several methods entirely from it.

What do we want is implement UNIQUE indexes with the UPPER function wrapper around field names [1]. 

This provides two benefits to us: 

1) case-insensitive uniqueness of the field or the fields combination

2) quick filtering using iexact lookup, which uses UPPER(<field>) LIKE <string> statement in SQL (at least for the Postgres)

I think, adding more flexibility in current indexes build logic would help to implement and further support custom indexes implementations (like django-partial-index) if we are not going to merge them in Django core or contrib.

[1] https://gist.github.com/GeyseR/363b4b9d2d1cd8c91d51ebfe9369a7ac

пт, 20 окт. 2017 г. в 14:37, Ashley Waite <ashley....@gmail.com>:

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