#34918: Assigning model instance to `_id`/attname field saves correctly, but
breaks
accessing the field
-------------------------------------+-------------------------------------
Reporter: Ricardo Busquet | Owner: nobody
Type: Bug | Status: new
Component: Database layer | Version: 4.2
(models, ORM) |
Severity: Normal | Resolution:
Keywords: | Triage Stage:
| Unreviewed
Has patch: 0 | Needs documentation: 0
Needs tests: 0 | Patch needs improvement: 0
Easy pickings: 0 | UI/UX: 0
-------------------------------------+-------------------------------------
Comment (by Tim Graham):
Django generally doesn't validate model attribute assignments. For
example, if Book has a title `CharField`, you can assign it the wrong
type, like `datetime` and it'll be silently coerced to string. I don't
think we're going to add this sort of validation or document it, but I
will leave this ticket open for a second opinion in case I'm overlooking
something.
Incidentally, similar steps with `id` as an `AutoField` also save
correctly but subsequently fail on access:
{{{ #!python
Traceback (most recent call last):
File
"/home/tim/code/django/django/db/models/fields/related_descriptors.py",
line 235, in __get__
rel_obj = self.field.get_cached_value(instance)
File "/home/tim/code/django/django/db/models/fields/mixins.py", line 15,
in get_cached_value
return instance._state.fields_cache[cache_name]
KeyError: 'reporter'
During handling of the above exception, another exception occurred:
Traceback (most recent call last):
File "/home/tim/code/django/django/db/models/fields/__init__.py", line
2116, in get_prep_value
return int(value)
TypeError: int() argument must be a string, a bytes-like object or a real
number, not 'Reporter'
The above exception was the direct cause of the following exception:
Traceback (most recent call last):
File "/home/tim/code/django/tests/many_to_one/tests.py", line 856, in
test_cached_relation_invalidated_on_save
self.assertEqual(self.a.reporter, self.r2)
File
"/home/tim/code/django/django/db/models/fields/related_descriptors.py",
line 253, in __get__
rel_obj = self.get_object(instance)
File
"/home/tim/code/django/django/db/models/fields/related_descriptors.py",
line 216, in get_object
return qs.get(self.field.get_reverse_related_filter(instance))
File "/home/tim/code/django/django/db/models/query.py", line 633, in get
clone = self._chain() if self.query.combinator else self.filter(*args,
**kwargs)
File "/home/tim/code/django/django/db/models/query.py", line 1476, in
filter
return self._filter_or_exclude(False, args, kwargs)
File "/home/tim/code/django/django/db/models/query.py", line 1494, in
_filter_or_exclude
clone._filter_or_exclude_inplace(negate, args, kwargs)
File "/home/tim/code/django/django/db/models/query.py", line 1501, in
_filter_or_exclude_inplace
self._query.add_q(Q(*args, **kwargs))
File "/home/tim/code/django/django/db/models/sql/query.py", line 1599,
in add_q
clause, _ = self._add_q(q_object, self.used_aliases)
File "/home/tim/code/django/django/db/models/sql/query.py", line 1631,
in _add_q
child_clause, needed_inner = self.build_filter(
File "/home/tim/code/django/django/db/models/sql/query.py", line 1458,
in build_filter
return self._add_q(
File "/home/tim/code/django/django/db/models/sql/query.py", line 1631,
in _add_q
child_clause, needed_inner = self.build_filter(
File "/home/tim/code/django/django/db/models/sql/query.py", line 1545,
in build_filter
condition = self.build_lookup(lookups, col, value)
File "/home/tim/code/django/django/db/models/sql/query.py", line 1375,
in build_lookup
lookup = lookup_class(lhs, rhs)
File "/home/tim/code/django/django/db/models/lookups.py", line 30, in
__init__
self.rhs = self.get_prep_lookup()
File "/home/tim/code/django/django/db/models/lookups.py", line 362, in
get_prep_lookup
return super().get_prep_lookup()
File "/home/tim/code/django/django/db/models/lookups.py", line 88, in
get_prep_lookup
return self.lhs.output_field.get_prep_value(self.rhs)
File "/home/tim/code/django/django/db/models/fields/__init__.py", line
2118, in get_prep_value
raise e.__class__(
TypeError: Field 'id' expected a number but got <Reporter: Paul Jones>.
}}}
--
Ticket URL: <https://code.djangoproject.com/ticket/34918#comment:2>
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