Re: [Django] #35958: QuerySet.distinct() crashes with "SELECT DISTINCT ON expressions must match initial ORDER BY expressions" (was: Issue with the distinct() function when specifying a field to run it on)

[Django]

#35958: QuerySet.distinct() crashes with "SELECT DISTINCT ON expressions must match
initial ORDER BY expressions"
-------------------------------------+-------------------------------------
Reporter: adofosam | Owner: (none)
Type: Bug | Status: new
Component: Database layer | Version: 5.1
(models, ORM) |
Severity: Normal | Resolution:
Keywords: distinct | Triage Stage:
| Unreviewed
Has patch: 0 | Needs documentation: 0
Needs tests: 0 | Patch needs improvement: 0
Easy pickings: 0 | UI/UX: 0
-------------------------------------+-------------------------------------
Changes (by Tim Graham):

* summary:
Issue with the distinct() function when specifying a field to run it
on
=>
QuerySet.distinct() crashes with "SELECT DISTINCT ON expressions must
match initial ORDER BY expressions"


Old description:

> When I attempt to run the following code, I get a error.
>
> Code:
> """
> user = User.objects.get(id=user_id)
> list = List.objects.filter(user=user).order_by('email').distinct('email')
> """
>
> Error (Context: my app is called "lists"):
> """
> django.db.utils.ProgrammingError: SELECT DISTINCT ON expressions must
> match initial ORDER BY expressions
> LINE 1: SELECT COUNT(*) FROM (SELECT DISTINCT ON ("lists_list"...
> """
>
> I'm using a postgresql database and my list model is as follows:
> """
> class EventList(models.Model): # List for Marketting
> id = models.UUIDField(primary_key=True, default=uuid.uuid4,
> editable=False, unique=True)
> user= models.ForeignKey(User, on_delete=models.CASCADE)
> email = models.EmailField()
> """

New description:

When I attempt to run the following code, I get an error.

Code:
{{{#!python
user = User.objects.get(id=user_id)
list = List.objects.filter(user=user).order_by('email').distinct('email')
}}}

Error (Context: my app is called "lists"):
{{{
django.db.utils.ProgrammingError: SELECT DISTINCT ON expressions must
match initial ORDER BY expressions
LINE 1: SELECT COUNT(*) FROM (SELECT DISTINCT ON ("lists_list"...
}}}

I'm using a PostgreSQL database and my model is:
{{{#!python
class EventList(models.Model):
id = models.UUIDField(primary_key=True, default=uuid.uuid4,
editable=False, unique=True)
user= models.ForeignKey(User, on_delete=models.CASCADE)
email = models.EmailField()
}}}

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Ticket URL: <https://code.djangoproject.com/ticket/35958#comment:1>
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