django 中的临时模型

Question

在一个 celery 任务中，我需要在数据库中创建临时 table。在 this article 中，Daniel Roseman 解释了如何创建一个。但是这个解决方案在 Django 1.9 中不起作用。我试图查看 Django 文档和 Google 但我找不到任何有用的东西。

上述文章中可在 Django 1.8 中运行的代码：

from django.db import models, cursor
from django.contrib.contenttypes.management import update_contenttypes
from django.core.management import call_command

class TempCustomerAddress(models.Model):
    address = models.ForeignKey('accounts.Address')
    legacy_id = models.CharField(max_length=12, unique=True)

    class Meta:
        app_label = 'utils'


class Command(NoArgsCommand):

    def handle_noargs(self, **options):
        models.register_models('utils', TempCustomerAddress)
        models.signals.post_syncdb.disconnect(update_contenttypes)
        call_command('syncdb')

        # ... do importing and stuff referring to TempCustomerAddress ...

        cursor = connection.cursor()
        cursor.execute('DROP TABLE `utils_tempcustomeraddress`')

Answer 1

在 django 1.9 中你实际上不需要注册任何东西。您只需按照与 models.py 相同的方式创建模型，仅此而已。您只需要确保它不在 models.py 文件中，因为它将成为永久模型。此示例假设您已经运行所有迁移。

from django.db import models, cursor
from django.contrib.contenttypes.management import update_contenttypes
from django.core.management import call_command

class TempCustomerAddress(models.Model):
    address = models.ForeignKey('accounts.Address')
    legacy_id = models.CharField(max_length=12, unique=True)

    class Meta:
        app_label = 'utils'


class Command(NoArgsCommand):

    def handle_noargs(self, **options):
        with connection.cursor() as cursor:
            cursor.execute('DROP TABLE IF EXISTS utils_tempcustomeraddress')
            cursor.execute('''
                CREATE TABLE utils_tempcustomeraddress (
                    id INTEGER PRIMARY KEY NOT NULL,
                    address_id REFERENCES accounts_address (id),
                    legacy_id VARCHAR(12) UNIQUE
                );
            '''
            # ... do importing and stuff referring to TempCustomerAddress ...

            cursor.execute('DROP TABLE `utils_tempcustomeraddress`')

Answer 2

我需要创建一个从 "permanent" 模型派生的临时模型，并使用临时 table 存储以避免污染永久模型的 table。经过大量探索，包括一篇与 Django 0.96, some newer material it points to for Django 1.2 and some old material 有关的文章，该文章基于集成到 Django 中的迁移技术，我终于想出了一个适用于 Django 2.0 的方法。

首先，我需要使用 Meta:

显式指定数据库 table 名称

model_name = re.sub('[@.]', '_', 'some_string')

class Meta:
    app_label = original_model._meta.app_label
    #
    # Use the explicit name for the database table.
    #
    db_table = '"' + model_name.lower() + '"'

然后我通过复制我需要的原始模型创建了模型class：

attr = {'__module__': __name__, 'Meta': Meta}
local_fields = [field.name for field in original_model._meta.local_fields]
for field in original_model._meta.fields:
    #
    # Clone only the fields which we need, not forgetting that we only
    # want one primary key.
    #
    clone = field.clone()
    if field.name in local_fields:
        local_fields.remove(field.name)
    else:
        clone.primary_key = False
    if not isinstance(field, (db_models.AutoField, db_models.OneToOneField, db_models.ManyToManyField)):
        attr[field.name] = clone
new_model = type(model_name, (db_models.Model,), attr)

困难的部分是追踪如何为模型创建新的 table。一旦找到，答案很简单：

from django.db import connection

with connection.schema_editor() as schema_editor:
    schema_editor.create_model(new_model)

django 中的临时模型

Temporary models in django

django

django-models

django-orm