1196998 - Error adding exclusion profile after update to Django 1.8 ("Non-relational field given in select_related: 'info'")

Status: RESOLVED FIXED

(Tree Management :: Treeherder, defect, P1)

Description

[Chris Manchester (limited bugmail, email directly)]

Attachment: Screenshot from 2015-08-20 16:24:48.png

I was trying to hide the GTest job I added in bug 1196464 and got the attached error. Not sure what's going on here, but the job is visible on try (and red) for now.

Comment 1

[Ed Morley [:emorley]]

This seems to be a Django 1.8 update regression:
https://docs.djangoproject.com/en/1.8/releases/1.8/#select-related-now-checks-given-fields

select_related() now validates that the given fields actually exist. Previously, nonexistent fields were silently ignored. Now, an error is raised:
...

The validation also makes sure that the given field is relational:

>>> book = Book.objects.select_related('name')
Traceback (most recent call last):
...
FieldError: Non-relational field given in select_related: 'name'

Comment 2

[Ed Morley [:emorley]]

The line in question is here:
https://github.com/mozilla/treeherder/blob/bae6e0492ac41f09279b13f7f23782f0f00ee370/treeherder/model/models.py#L451

So select_related() is documented here:
https://docs.djangoproject.com/en/1.8/ref/models/querysets/#select-related

However one thing it doesn't make that clear, but that is mentioned here:
http://timmyomahony.com/blog/misconceptions-select_related-in-django/

...is that it cannot be used for ManyToMany, but yet that's what we're doing here:
https://github.com/mozilla/treeherder/blob/bae6e0492ac41f09279b13f7f23782f0f00ee370/treeherder/model/models.py#L419

Comment 3

[Ed Morley [:emorley]]

(Meant to say: that same blog article suggests using prefetch-related instead:
https://docs.djangoproject.com/en/1.8/ref/models/querysets/#prefetch-related )

Comment 4

[Treeherder GitHub Bugbot]

Commit pushed to master at https://github.com/mozilla/treeherder

https://github.com/mozilla/treeherder/commit/c8c84e3d1a15dbe65e88e68d300a925e5322a2ba
Bug 1196998 - Error adding exclusion profile after update to Django 1.8

We were calling select_related on a non-relational field.  Only became
an issue with Django 1.8.

Comment 5

[Mauro Doglio [:mdoglio]]

:emorley the line you highlighted is defining a ManyToMany field. The `related_name` parameter is the name of the attribute the related class will use to refer to this one. I didn't know about the prefetch_related method, they must have added it in the last couple of versions of django :-)

Comment 6

[Ed Morley [:emorley]]

(In reply to Mauro Doglio [:mdoglio] from comment #5)
> :emorley the line you highlighted is defining a ManyToMany field. The
> `related_name` parameter is the name of the attribute the related class will
> use to refer to this one. I didn't know about the prefetch_related method,
> they must have added it in the last couple of versions of django :-)

I'm not sure I understand this reply? Do you mean the current fix here was correct, or not? (It actually doesn't use prefetch_related, it removes select_related entirely) :-)

Comment 7

[Cameron Dawson [:camd]]

I'm pretty sure just removing that was the right call.  But feel free to double-check me, if I'm missing something.  :)

The self.exclusions.all() is fetching all the rows of the JobExclusion model.  The field of ``info`` is in that model.  It's not a foreign key or a m2m relation.  It was just superfluous.