Inconsistent FieldError message under some circumstances

[Thomas C]

Under some circumstances, FieldError are raised with inconsistent messages Cannot resolve keyword u'name' into field. Choices are: name, ...

Reproduced with the following code :

# Model
class Tag(models.Model):
    name = models.CharField(max_length=10)
    parent = models.ForeignKey('self', blank=True, null=True,
            related_name='children')
    category = models.ForeignKey(NamedCategory, null=True, default=None)

# FieldError
Tag.objects.values_list('name__foo')

[Thomas C]

Proposed patch ​https://github.com/django/django/pull/3188

[Baptiste Mispelon]

Hi,

I agree that we should try and improve the message.
However, your proposed patch now generates the following message:

Cannot resolve keyword 'foo' into field. Choices are: category, category_id, children, id, name, parent, parent_id

I'm not sure if that's an improvement since this message seems to indicate that doing name__category would be valid.

Instead, I think the error message should say that name is not a field you can "jump" with the double underscore syntax (I'm not sure what the correct term for that is).
Looking at the code, this will probably require some more in-depth changes since the exit condition of the loop conflates non-existing field names and fields that can't be "jumped".

Thanks.

[Thomas C]

You're right indeed, I missed that part of the message.

[Thomas C]

I updated my PR after bmispelon comment.

[Tim Graham]

Don't forget to uncheck "Patch needs improvement" so the ticket appears in the review queue. The patch looks okay to me, but would be good to have another review from an ORM expert to make sure nothing has been overlooked.

[Loic Bistuer <loic.bistuer@…>]

In e008a10c2ffef7d64100bcbe83ef2c5f4b1b2168:

Fixed #23443 -- Corrected erroneous FieldError message.

Thanks Tim Graham for the review.