在Django中复制模型实例及其相关对象/用于可复制对象的算法

  • Z时代
  • 2024-01-10
  • 分类：问答

我已经为模型Books，Chapters和Pages。它们全部由编写User：

from django.db import models
class Book(models.Model)
    author = models.ForeignKey('auth.User')
class Chapter(models.Model)
    author = models.ForeignKey('auth.User')
    book = models.ForeignKey(Book)
class Page(models.Model)
    author = models.ForeignKey('auth.User')
    book = models.ForeignKey(Book)
    chapter = models.ForeignKey(Chapter)

我想做的就是复制一个现有的Book并更新User给其他人。皱纹是我也想复制所有相关模型实例的Book-它所有的Chapters和Pages以及！

观察时，事情变得非常棘手Page-不仅Pages需要author更新其字段，而且还需要指向新Chapter对象！

Django是否支持开箱即用的方式？用于复制模型的通用算法是什么样的？

回答：

由于删除了CollectedObjects，因此它在Django 1.3中不再起作用。参见变更集14507

我在Django片段上发布了我的解决方案。它很大程度上取决于django.db.models.query.CollectedObject用于删除对象的代码：

from django.db.models.query import CollectedObjects
from django.db.models.fields.related import ForeignKey
def duplicate(obj, value, field):
    """
    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`.  
    """
    collected_objs = CollectedObjects()
    obj._collect_sub_objects(collected_objs)
    related_models = collected_objs.keys()
    root_obj = None
    # Traverse the related models in reverse deletion order.    
    for model in reversed(related_models):
        # 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.
        sub_obj = collected_objs[model]
        for pk_val, obj in sub_obj.iteritems():
            for fk in fks:
                fk_value = getattr(obj, "%s_id" % fk.name)
                # If this FK has been duplicated then point to the duplicate.
                if fk_value in collected_objs[fk.rel.to]:
                    dupe_obj = collected_objs[fk.rel.to][fk_value]
                    setattr(obj, fk.name, dupe_obj)
            # Duplicate the object and save it.
            obj.id = None
            setattr(obj, field, value)
            obj.save()
            if root_obj is None:
                root_obj = obj
    return root_obj

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