Apply data structure best practices to the django.contrib models and docs

[Jon Dufresne]

In PR ​https://github.com/django/django/pull/11267 an argument is presented that explains why list is often the best choice for Model.Meta data structures. This landed as ​https://github.com/django/django/commit/97d3321e89c8d4434927bdbc308db1ccffa99d3b.

Now change all models in django.contrib to follow our own stated best practices. People often look at existing examples for how to write new code, so we might as well promote the standards we document.

[Jon Dufresne]

Updated PR.

[Carlos_Mir_de_Souza]

It`s ok.

[Jon Dufresne <jon.dufresne@…>]

In e5cacb1:

Refs #30947 -- Changed tuples to lists in model Meta options examples in docs.

Follow up to 97d3321e89c8d4434927bdbc308db1ccffa99d3b.

[Mariusz Felisiak <felisiak.mariusz@…>]

In b9fe7f92:

Fixed #30947 -- Changed tuples to lists in model Meta options in django.contrib modules.

The Django "Model Meta options" docs provide examples and generally
point the reader to use lists for the unique_together and ordering
options. Follow our own advice for contrib models.

More generally, lists should be used for homogeneous sequences of
arbitrary lengths of which both unique_together and ordering are.

[Mariusz Felisiak <felisiak.mariusz@…>]

In 2000ed51:

[3.0.x] Refs #30947 -- Changed tuples to lists in model Meta options examples in docs.

Follow up to 97d3321e89c8d4434927bdbc308db1ccffa99d3b.

Backport of e5cacb1f47cb3a2943bbc7685a630c84503b0d1b from master

[Mariusz Felisiak <felisiak.mariusz@…>]

In a7f90d9:

[2.2.x] Refs #30947 -- Changed tuples to lists in model Meta options examples in docs.

Follow up to 97d3321e89c8d4434927bdbc308db1ccffa99d3b.

Backport of e5cacb1f47cb3a2943bbc7685a630c84503b0d1b from master

[Mariusz Felisiak]

#30947 was a duplicate for extra docs changes.

[Ojas Gupta]

Ok so I have to convert tuple of list to list of list.

[Alex Morega]

This is actually a pet peeve of mine; would love to see the docs updated to using lists instead of tuples.

Would this be a good checklist of places to update in the codebase and docs? ​https://gist.github.com/mgax/32318118a71ce602a00a80daeecb60fc

[Simon Charette]

Some of the examples you pointed should remain tuples as they are mixing heterogenous data and mostly used to a define a schema over data.

Since we're on the topic of data structure best practices unique_together and friends should likely be defined as set and not list as only unique entries will be considered and because the order in which they are defined on the model doesn't have any significance.

[Alex Morega]

Some of the examples you pointed should remain tuples as they are mixing heterogenous data and mostly used to a define a schema over data.

Right! I meant it as a starting point of places that might need fixing.

Since we're on the topic of data structure best practices unique_together and friends should likely be defined as set and not list as only unique entries will be considered and because the order in which they are defined on the model doesn't have any significance.

I see your point, but AFAIU, a side effect of unique_together is creating composite database indexes, where the ​order of columns matters.

There hasn't been any activity on the ticket for 3 weeks; may I take ownership?

[Simon Charette]

I see your point, but AFAIU, a side effect of unique_together is creating composite database indexes, where the ​order of columns matters.

The order of columns within an index or unique constraints matter, but the order of constraints doesn't. This obviously means that you can't use the flattened syntax index_together = {'foo', 'bar'} but favor index_together = {('foo', 'bar')}.

[Alex Morega]

​PR

[Mariusz Felisiak <felisiak.mariusz@…>]

In de6c9c7:

Refs #30947 -- Changed tuples to lists where appropriate.