unique_for_date and friends should create database indexes where possible

[sam@…]

Currently the field options unique_for_date, etc. do not create database indexes. I think this should be changed where the database backend supports this.

For example, with PostgreSQL:

db=> CREATE TABLE FOO (date timestamp with time zone, slug text);
db=> CREATE UNIQUE INDEX foo_unqiue_date ON foo (date_trunc ('day', date AT TIME ZONE 'UTC'), slug);
db=> INSERT INTO FOO VALUES (now(), 'slug1');
INSERT 0 1
db=> INSERT INTO FOO VALUES (now(), 'slug2');
INSERT 0 1
db=> INSERT INTO FOO VALUES (now(), 'slug1');
ERROR:  duplicate key violates unique constraint "foo_unique_date"

The date_trunc function can be used to truncate the timestamp data to any desired precision, so it can be used for the other unqiue_for attributes.

[Aymeric Augustin]

Change UI/UX from NULL to False.

[Aymeric Augustin]

Change Easy pickings from NULL to False.

[Aymeric Augustin]

Since time zone support was added, ​the check is performed in the current time zone. In general, it's impossible to make a database index change dynamically when the time zone changes in the application. If you have a more restricted use case, you can add the index with a migration.