在 Django 中将字段从一个实例复制到另一个实例

我有以下代码，它采用现有实例并在另一个模型中复制或“存档”它，然后删除它，用草稿副本替换它。

当前代码

def archive_calc(self, rev_num, primary_field):
    model_a = Calc.objects.get(tag_number__tag_number = primary_field, revision_number = rev_num) #Current Revision instance
    model_b = CalcArchive() #Draft instance

    #Copies data to archive model
    for field in model_a._meta.fields:
        setattr(model_b, field.name, getattr(model_a, field.name))

    model_b.pk = None
    model_b.current_revision = False
    model_b.save()

    model_a.delete()

这工作正常，但是我需要更改系统以允许某些具有外键的模型，因为当归档/删除实例时，相关记录也会随之删除。因此，我解决此问题的想法是将草稿记录中的更改复制到先前的记录，然后删除草稿，从而维护外键相关记录。

解决思路

def archive_calc(self, rev_num, primary_field):
    model_a = Calc.objects.get(tag_number__tag_number = primary_field, revision_number = rev_num) #Current Revision instance
    model_b = CalcArchive() #Archive Instance
    model_c = Calc.objects.get(pk = self.object.pk) #Draft instance

    #Copies data to archive model
    for field in model_a._meta.fields:
        setattr(model_b, field.name, getattr(model_a, field.name))

    model_b.pk = None
    model_b.current_revision = False
    model_b.save()

    #Copies data from draft instance to current revision instance
    for field in model_c._meta.fields:
        setattr(model_a, field.name, getattr(model_c, field.name))

    model_c.delete()

不幸的是，上述解决方案不起作用，它似乎只是忽略了副本并继续按照“当前代码”工作。如果我添加model_a.save() after for field in model_c._meta.fi...系统陷入循环并最终抛出maximum recursion depth exceeded in cmp.

与往常一样，任何帮助将不胜感激，如果我找错了树，请告诉我。

经过大量研究和阅读 Django 文档后，我想出了一个看起来相当不错、简单的解决方案。

def archive_calc(self, rev_num, primary_field):
    model_a = Calc.objects.get(calc_details__calc_serial_number = primary_field, revision_number = rev_num)
    model_b = CalcArchive()

    object_list_annual = model_a.calcreview_set.filter(calc__calc_details = primary_field)
    object_list_ageing = model_a.calcitem_set.filter(calc__calc_details = primary_field)

    for obj in object_list_annual:
        obj.calc_id = self.object.id
        obj.save()
    for obj in object_list_ageing:
        obj.calc_id = self.object.id
        obj.save()

    for field in model_a._meta.fields:
        setattr(model_b, field.name, getattr(model_a, field.name))
    model_b.pk = None
    model_b.current_revision = False
    model_b.save()

    model_a.delete()

这通过设置“移动”相关对象_id字段与self.object.id.

我已经运行了几次测试，这似乎完全达到了我所寻找的目标，只需最少的代码，无需额外安装。

希望这对某人有帮助，并请随时指出我的回答中任何潜在的陷阱。