Version of ManyToManyField that can be set even if it relies on a intermediary model.
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 | class IntermediatedManyToManyField(ManyToManyField):
"""
ManyToManyField that can be set even if it relies on a intermediary model.
"""
def contribute_to_class(self, cls, name):
super(IntermediatedManyToManyField, self).contribute_to_class(cls, name)
# Override the descriptor for the m2m relation
setattr(
cls,
self.name,
_ReverseIntermediatedManyRelatedObjectsDescriptor(self),
)
class _ReverseIntermediatedManyRelatedObjectsDescriptor(
ReverseManyRelatedObjectsDescriptor
):
def __set__(self, instance, new_related_values):
if instance is None:
raise AttributeError('Manager must be accessed via instance')
manager = self.__get__(instance)
pre_existing_values = manager.all()
new_related_value_pks = [
new_related_value.pk for new_related_value in new_related_values]
values_to_unrelate = pre_existing_values.exclude(
pk__in=new_related_value_pks)
values_to_unrelate.delete()
# Create relationships for values not previously related, leaving alone
# those which exist already
intermediary_model = self.field.rel.through
instance_field_name = manager.source_field_name
related_field_name = manager.target_field_name
for related_value in new_related_values:
if related_value not in pre_existing_values:
intermediary_model.objects.create(**{
instance_field_name: instance,
related_field_name: related_value,
})
|
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