Duplicating model instances and their related objects in Django / Algorithm for recusrively duplicating an object

Question

I\'ve models for Books, Chapters and Pages. They are all written by a User:

from django.db import models
         


        

Answer 1

Elaborated based on previous answers:

def derive(obj):
    import copy
    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 duplicate all related fields to point 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

Answer 2

Django does have a built-in way to duplicate an object via the admin - as answered here: In the Django admin interface, is there a way to duplicate an item?

Answer 3

Suggestion of Julio Marins works! Thnx!

For Django >= 2.* this line:

if isinstance(f, ForeignKey) and f.rel.to in related_models:

Should be replaced with:

if isinstance(f, ForeignKey) and f.remote_field.model in related_models:

Answer 4

In Django 1.5 this works for me:

thing.id = None
thing.pk = None
thing.save()

Answer 5

Here's an easy way to copy your object.

Basically:

(1) set the id of your original object to None:

book_to_copy.id = None

(2) change the 'author' attribute and save the ojbect:

book_to_copy.author = new_author

book_to_copy.save()

(3) INSERT performed instead of UPDATE

(It doesn't address changing the author in the Page--I agree with the comments regarding re-structuring the models)