Django“ValueError：无法批量创建多表继承模型”

Question

问题

我正在使用 django-model-utils InheritanceManager。我有一个超级 Notification(models.Model) 类，我用它来创建许多通知子类，例如 PostNotification(Notification)、CommentNotification(Notification) 等，当尝试运行 CommentNotification.objects.bulk_create(list_of_comment_notification_objects) 时，我得到以下回溯：

File "/home/me/.virtualenvs/project/local/lib/python2.7/site-packages/django/db/models/query.py", line 429, in bulk_create
    raise ValueError("Can't bulk create a multi-table inherited model")
ValueError: Can't bulk create a multi-table inherited model

在检查 query.py 文件后，我们发现这会导致错误：

for parent in self.model._meta.get_parent_list():
      if parent._meta.concrete_model is not self.model._meta.concrete_model:
           raise ValueError("Can't bulk create a multi-table inherited model")

环境 Django 模型工具版本：3.1.1 Django 版本：1.11.7 Python 版本：2.7.3

示例

PostNotification.objects.bulk_create(
   [PostNotification(related_user=user, post=instance) for user in users]
)

抛出上述异常

我已经尝试过，虽然最初是成功的：

我虽然只是运行： BaseClass.objects.bulk_create(list_of_SubClass_objects) 而不是 SubClass.objects.bulk_create(list_of_SubClass_objects) 将起作用并返回子类值列表，但随后运行 SubClass.objects.all() 将返回空结果。 bulk_create() 只会为列表中的每个项目创建一个 Notification 基类对象。

Answer 1

我已经完成了bulk_create 的自定义实现，这似乎适用于我的情况（只有一个父关系，而不是自动递增的 pk）：

from django.db import models


class MultiTableChildQueryset(models.QuerySet):

    def bulk_create(self, objs, batch_size=None):
        assert batch_size is None or batch_size > 0
        if not objs:
            return objs

        self._for_write = True
        objs = list(objs)
        parent_model = self.model._meta.pk.related_model

        parent_objs = []
        for obj in objs:
            parent_values = {}
            for field in [f for f in parent_model._meta.fields if hasattr(obj, f.name)]:
                parent_values[field.name] = getattr(obj, field.name)
            parent_objs.append(parent_model(**parent_values))
            setattr(obj, self.model._meta.pk.attname, obj.id)
        parent_model.objects.bulk_create(parent_objs, batch_size=batch_size)

        with transaction.atomic(using=self.db, savepoint=False):
            self._batched_insert(objs, self.model._meta.local_fields, batch_size)

        return objs

Answer 2

找到了一个 hacky 解决方案。我希望它适用于你的情况。诀窍是动态创建一个模型（不是继承的），它有一些元（db_table）集。并使用此动态模型批量创建 Child 对象（即写入 Child 的 DB 表）。

    class Parent(models.Model):
        name = models.CharField(max_length=10)


    class Child(Parent):
        phone = models.CharField(max_length=12)

# just an example. Should be expanded to work properly.
field_type_mapping = {
    'OneToOneField': models.IntegerField,
    'CharField': models.CharField,
}

def create_model(Model, app_label='children', module='', options=None):
    """
    Create specified model
    """
    model_name = Model.__name__
    class Meta:
       managed = False
       db_table = Model._meta.db_table

    if app_label:
        # app_label must be set using the Meta inner class
        setattr(Meta, 'app_label', app_label)

    # Update Meta with any options that were provided
    if options is not None:
        for key, value in options.iteritems():
            setattr(Meta, key, value)

    # Set up a dictionary to simulate declarations within a class
    attrs = {'__module__': module, 'Meta': Meta}

    # Add in any fields that were provided
    fields = dict()
    for field in Model._meta.fields:
        if field.attname == 'id':
            continue
        if field.model.__name__ == model_name:
            field_class_name = type(field).__name__
            print(field.attname)
            fields[field.attname] = field_type_mapping[field_class_name]()
    # Create the class, which automatically triggers ModelBase processing
    attrs.update(fields)

    model = type(f'{model_name}Shadow', (models.Model,), attrs)


    return model

mod = create_model(Child)
parents = [Parent(name=i) for i in range(15)]
parents = Parent.objects.bulk_create(parents)
children = [mod(phone=parent.name, parent_ptr_id=parent.id) for parent in parents]
mod.objects.bulk_create(children)