Add an example for contrib.postgres.aggregates.StringAgg to docs.

[Mark Gensler]

The documentation is missing an example for StringAgg. Also I thought it would be useful to include an example for ManyToMany fields, in contrast to the OneToMany example for JSONBAgg.

I.e.

class Publication(models.Model):
        title = models.CharField(max_length=30)

class Article(model.Model):
        headline = models.CharField(max_length=100)
        publications = models.ManyToManyField(Publication)

>>> article = Article.objects.create(headline='NASA uses Python')
>>> article.publications.create(title='The Python Journal')
>>> article.publications.create(title='Science News')

>>> from django.contrib.postgres.aggregates import StringAgg
>>> Article.objects.annotate(
...     publication_names=StringAgg(
...         'publications__title',
...         delimiter=', ',
...         ordering='publications__title',
...     )
... ).values('headline', 'publication_names')
<QuerySet [{
    'headline': 'NASA uses Python', 'publication_names': 'Science News, The Python Journal'
]}]>

[David Sanders]

Hi Mark,

Thanks for the input!

Just FYI you don't need a ticket for trivial documentation updates. I think an example like this may fall under that category 👍

[Mark Gensler]

Hi David, you're welcome! Thanks for letting me know, I will just make a PR for something like this in future.

Mark

[Mariusz Felisiak]

​PR

[Mariusz Felisiak <felisiak.mariusz@…>]

In 34459389:

Fixed #34199 -- Added example to StringAgg docs.

[Mariusz Felisiak <felisiak.mariusz@…>]

In 29c9bba8:

[4.1.x] Fixed #34199 -- Added example to StringAgg docs.

Backport of 344593893b6fc5fdda45a74013fc8622401c5058 from main