derive.py

derive.py

def derive(obj):
    from django.contrib.admin.utils import NestedObjects
    from django.db import DEFAULT_DB_ALIAS
    from django.db.models.fields.related import ForeignKey
    """
        Derive a new model instance from previous one,
        and point all related fields to the new instance
    """
    obj2 = copy.copy(obj)
    obj2.pk = None
    obj2.save()
    collector = NestedObjects(using=DEFAULT_DB_ALIAS)
    collector.collect([obj])
    collector.sort()
    related_models = collector.data.keys()
    data_snapshot = {}

    for key in collector.data.keys():
        data_snapshot.update({
            key: dict(
                zip(
                    [item.pk for item in collector.data[key]],
                    [item for item in collector.data[key]]
                )
            )
        })

    duplicate_order = reversed(related_models)

    for model in duplicate_order:
        # Find all FKs on model that point to a related_model.
        fks = []
        for f in model._meta.fields:
            if isinstance(f, ForeignKey) and f.rel.to in related_models:
                fks.append(f)
        # Replace each `sub_obj` with a duplicate.
        if model not in collector.data:
            continue
        sub_objects = collector.data[model]
        for obj in sub_objects:
            for fk in fks:
                dupe_obj = copy.copy(obj)
                setattr(dupe_obj, fk.name, obj2)
                dupe_obj.pk = None
                dupe_obj.save()
    return obj2