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

this is an edit of http://www.djangosnippets.org/snippets/1282/

It's now compatible with the Collector which replaced CollectedObjects in 1.3.

I didn't really test this too heavily, but did test it with an object with about 20,000 sub-objects, but in only about three layers of foreign-key depth. Use at your own risk of course.

For the ambitious guy who reads this post, you should consider subclassing Collector (or copying the entire class to remove this dependency on this unpublished section of the django API) to a class called something like "DuplicateCollector" and writing a .duplicate method that works similarly to the .delete method. that would solve this problem in a real way.

from django.db.models.deletion import Collector
from django.db.models.fields.related import ForeignKey

def duplicate(obj, value=None, field=None, duplicate_order=None):
    """
    Duplicate all related objects of obj setting
    field to value. If one of the duplicate
    objects has an FK to another duplicate object
    update that as well. Return the duplicate copy
    of obj.
    duplicate_order is a list of models which specify how
    the duplicate objects are saved. For complex objects
    this can matter. Check to save if objects are being
    saved correctly and if not just pass in related objects
    in the order that they should be saved.
    """
    collector = Collector({})
    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]])) })
    root_obj = None

    # Sometimes it's good enough just to save in reverse deletion order.
    if duplicate_order is None:
        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:
                fk_value = getattr(obj, "%s_id" % fk.name)
                # If this FK has been duplicated then point to the duplicate.
                fk_rel_to = data_snapshot[fk.rel.to]
                if fk_value in fk_rel_to:
                    dupe_obj = fk_rel_to[fk_value]
                    setattr(obj, fk.name, dupe_obj)
            # Duplicate the object and save it.
            obj.id = None
            if field is not None:
                setattr(obj, field, value)
            obj.save()
            if root_obj is None:
                root_obj = obj
    return root_obj

EDIT: Removed a debugging "print" statement.