Is there a way to keep a Django model instance, which is referenced by foreign keys, in memory without storing it to the database?
The code is part of an _add_ overload, but the way it is implemented now is very ugly as it is hard to keep track of the new instances, and it also produces a lot of unnecessary DB accesses. Ideally I want to keep the new instances temporary as long as the user does not call the save() method on the returned instance.
When I uncomment the save() calls like below, the SequenceAnnotation instances are not referenced in the returned Sequence instance.
def __add__(self, other: Union['Sequence', str]):
"""
This enables you to use the + operator when dealing with Sequence objects
:param other:
:return:
"""
sum_seq = Sequence()
# concatenate the actual sequences
sum_seq.sequence = self.sequence + other.sequence
#sum_seq.save()
len_self_seq = len(self.sequence)
# annotations
annot: SequenceAnnotation
# copy the own anntotations
for annot in self.annotations.all():
new_annot = deepcopy(annot)
new_annot.id = None # this is crucial to actually create a new instance
new_annot.ref_sequence = sum_seq
#new_annot.save()
# copy the other annotations, adjust the start and end positions
for annot in other.annotations.all():
new_annot = deepcopy(annot)
new_annot.id = None # this is crucial to actually create a new instance
new_annot.start = len_self_seq + annot.start
new_annot.end = len_self_seq + annot.end
new_annot.ref_sequence = sum_seq
#new_annot.save()
return sum_seq
No, as far as I know.
Django foreign key fields are backed by something_id fields; assigning foo.something to something that has a None id sets the backing field to None.
You would need to implement something similar to how forms (may) have save_m2m() to ensure the constellation of objects gets saved in the right order.