Get difference of foreign key attribute with django - django

Question

I'm trying to get a queryset where a Task has two Issuances which have been created within 10 seconds of one another.
Models are as follows:
Class Task(models.Model):
# stuff
Class Issuance(models.Model):
task = models.ForeignKey(Task, blank=True, null=True, on_delete=models.SET_NULL)
created = models.DateTimeField(default=timezone.now)
What I've got so far:
qs = (
Task.objects
.annotate(count=Count('issuance'))
.filter(count__gt=1, count__lte=2)
.annotate(time_difference=F('issuance__created')) # Need to fix this
.annotate(
dupe=Case(
When(
time_difference__lt=10, # Less than 10 seconds
then=Value(1),
),
default=Value(0),
output=BooleanField(),
)
)
)
I think I'm pretty close but I need some way to calculate the time difference between the creation date of the two issuances for any one Task. Also, need to do a comparison that the time delta is less than 10 seconds; not sure if what I have will work.
Can anyone help, please?
EDIT: Added output of query
TypeError Traceback (most recent call last)
<ipython-input-47-e0e60776551e> in <module>()
11 ),
12 default=Value(0),
---> 13 output=BooleanField(),
14 )
15 )
/usr/local/lib/python3.6/site-packages/django/db/models/query.py in annotate(self, *args, **kwargs)
912 raise ValueError("The annotation '%s' conflicts with a field on "
913 "the model." % alias)
--> 914 clone.query.add_annotation(annotation, alias, is_summary=False)
915
916 for alias, annotation in clone.query.annotations.items():
/usr/local/lib/python3.6/site-packages/django/db/models/sql/query.py in add_annotation(self, annotation, alias, is_summary)
969 """
970 annotation = annotation.resolve_expression(self, allow_joins=True, reuse=None,
--> 971 summarize=is_summary)
972 self.append_annotation_mask([alias])
973 self.annotations[alias] = annotation
/usr/local/lib/python3.6/site-packages/django/db/models/expressions.py in resolve_expression(self, query, allow_joins, reuse, summarize, for_save)
827 c.is_summary = summarize
828 for pos, case in enumerate(c.cases):
--> 829 c.cases[pos] = case.resolve_expression(query, allow_joins, reuse, summarize, for_save)
830 c.default = c.default.resolve_expression(query, allow_joins, reuse, summarize, for_save)
831 return c
/usr/local/lib/python3.6/site-packages/django/db/models/expressions.py in resolve_expression(self, query, allow_joins, reuse, summarize, for_save)
760 c.is_summary = summarize
761 if hasattr(c.condition, 'resolve_expression'):
--> 762 c.condition = c.condition.resolve_expression(query, allow_joins, reuse, summarize, False)
763 c.result = c.result.resolve_expression(query, allow_joins, reuse, summarize, for_save)
764 return c
/usr/local/lib/python3.6/site-packages/django/db/models/query_utils.py in resolve_expression(self, query, allow_joins, reuse, summarize, for_save)
79 # We must promote any new joins to left outer joins so that when Q is
80 # used as an expression, rows aren't filtered due to joins.
---> 81 clause, joins = query._add_q(self, reuse, allow_joins=allow_joins, split_subq=False)
82 query.promote_joins(joins)
83 return clause
/usr/local/lib/python3.6/site-packages/django/db/models/sql/query.py in _add_q(self, q_object, used_aliases, branch_negated, current_negated, allow_joins, split_subq)
1251 child, can_reuse=used_aliases, branch_negated=branch_negated,
1252 current_negated=current_negated, connector=connector,
-> 1253 allow_joins=allow_joins, split_subq=split_subq,
1254 )
1255 joinpromoter.add_votes(needed_inner)
/usr/local/lib/python3.6/site-packages/django/db/models/sql/query.py in build_filter(self, filter_expr, branch_negated, current_negated, can_reuse, connector, allow_joins, split_subq)
1141 clause = self.where_class()
1142 if reffed_expression:
-> 1143 condition = self.build_lookup(lookups, reffed_expression, value)
1144 clause.add(condition, AND)
1145 return clause, []
/usr/local/lib/python3.6/site-packages/django/db/models/sql/query.py in build_lookup(self, lookups, lhs, rhs)
1081 lhs = self.try_transform(lhs, name, lookups)
1082 final_lookup = lhs.get_lookup('exact')
-> 1083 return final_lookup(lhs, rhs)
1084 lhs = self.try_transform(lhs, name, lookups)
1085 lookups = lookups[1:]
/usr/local/lib/python3.6/site-packages/django/db/models/lookups.py in __init__(self, lhs, rhs)
17 def __init__(self, lhs, rhs):
18 self.lhs, self.rhs = lhs, rhs
---> 19 self.rhs = self.get_prep_lookup()
20 if hasattr(self.lhs, 'get_bilateral_transforms'):
21 bilateral_transforms = self.lhs.get_bilateral_transforms()
/usr/local/lib/python3.6/site-packages/django/db/models/lookups.py in get_prep_lookup(self)
57 return self.rhs._prepare(self.lhs.output_field)
58 if self.prepare_rhs and hasattr(self.lhs.output_field, 'get_prep_value'):
---> 59 return self.lhs.output_field.get_prep_value(self.rhs)
60 return self.rhs
61
/usr/local/lib/python3.6/site-packages/django/db/models/fields/__init__.py in get_prep_value(self, value)
1415
1416 def get_prep_value(self, value):
-> 1417 value = super(DateTimeField, self).get_prep_value(value)
1418 value = self.to_python(value)
1419 if value is not None and settings.USE_TZ and timezone.is_naive(value):
/usr/local/lib/python3.6/site-packages/django/db/models/fields/__init__.py in get_prep_value(self, value)
1273 def get_prep_value(self, value):
1274 value = super(DateField, self).get_prep_value(value)
-> 1275 return self.to_python(value)
1276
1277 def get_db_prep_value(self, value, connection, prepared=False):
/usr/local/lib/python3.6/site-packages/django/db/models/fields/__init__.py in to_python(self, value)
1376
1377 try:
-> 1378 parsed = parse_datetime(value)
1379 if parsed is not None:
1380 return parsed
/usr/local/lib/python3.6/site-packages/django/utils/dateparse.py in parse_datetime(value)
91 Returns None if the input isn't well formatted.
92 """
---> 93 match = datetime_re.match(value)
94 if match:
95 kw = match.groupdict()
TypeError: expected string or bytes-like object