Question

我正在尝试使用现有数据转发模型。该模型有一个新的字段，其约束唯一= True和null = False。当我做的时候

./manage.py schemamigration myapp --auto

South让我通过询问：

为新字段指定默认值

Specify a one-off value to use for existing columns now

通常我将此设置为无，但由于此字段必须是唯一的，我想知道是否可以通过以下方式传递南方的唯一值：

 >>> import uuid; uuid.uuid1().hex[0:35]

这给了我一条错误消息

! Invalid input: invalid syntax

在通过命令行迁移时是否可以传递南方随机唯一默认值？

感谢。

Answer 1

不幸的是，只有datetime模块可用作模式迁移中的一次性值。

但是，您可以通过将其拆分为三次迁移来实现相同的效果：

在没有约束的情况下向模型添加新字段（使用null = True，unique = False）
使用数据迁移将UUID添加到新字段
在新字段上添加约束（使用null = False，unique = True）

数据迁移教程：http://south.readthedocs.org/en/0.7.6/tutorial/part3.html#data-migrations

Answer 2

在django 1.7+中，您可以执行以下操作。它首先添加没有索引的字段，也没有唯一的。然后它分配唯一值（我根据名称和你需要创建的slugify方法），最后再次改变字段以添加索引和唯一属性。

char* result = NULL;
char delims[] = {'"', ' '}; // split on spaces and double quotes
char check[] = {"Date","Time","Volt","Amp","Wirkfaktor"};
result = (char*)strtok( data, delims );
int i = 0;
while(result != NULL) {
    if(strcmp(result,check[i]) {
        printf("File Invalid\n");
        exit(0);
    }
    result = (char*)strtok( NULL, delims);
    i++;
}
// If we get here than the file was good.

Answer 3

Here是Django关于迁移独特字段的官方方法。

Migrations that add unique fields
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

 Applying a "plain" migration that adds a unique non-nullable field to a table
 with existing rows will raise an error because the value used to populate
 existing rows is generated only once, thus breaking the unique constraint.

 Therefore, the following steps should be taken. In this example, we'll add a
 non-nullable :class:`~django.db.models.UUIDField` with a default value. Modify
 the respective field according to your needs.

 * Add the field on your model with ``default=...`` and ``unique=True``
   arguments. In the example, we use ``uuid.uuid4`` for the default.

 * Run the :djadmin:`makemigrations` command.

 * Edit the created migration file.

   The generated migration class should look similar to this::

     class Migration(migrations.Migration):

         dependencies = [
             ('myapp', '0003_auto_20150129_1705'),
         ]

         operations = [
             migrations.AddField(
                 model_name='mymodel',
                 name='uuid',
                 field=models.UUIDField(max_length=32, unique=True, default=uuid.uuid4),
             ),
         ]

   You will need to make three changes:

   * Add a second :class:`~django.db.migrations.operations.AddField` operation
     copied from the generated one and change it to
     :class:`~django.db.migrations.operations.AlterField`.

   * On the first operation (``AddField``), change ``unique=True`` to
     ``null=True`` -- this will create the intermediary null field.

   * Between the two operations, add a
     :class:`~django.db.migrations.operations.RunPython` or
     :class:`~django.db.migrations.operations.RunSQL` operation to generate a
     unique value (UUID in the example) for each existing row.

   The resulting migration should look similar to this::

     # -*- coding: utf-8 -*-
     from __future__ import unicode_literals

     from django.db import migrations, models
     import uuid

     def gen_uuid(apps, schema_editor):
         MyModel = apps.get_model('myapp', 'MyModel')
         for row in MyModel.objects.all():
             row.uuid = uuid.uuid4()
             row.save()

     class Migration(migrations.Migration):

         dependencies = [
             ('myapp', '0003_auto_20150129_1705'),
         ]

         operations = [
             migrations.AddField(
                 model_name='mymodel',
                 name='uuid',
                 field=models.UUIDField(default=uuid.uuid4, null=True),
             ),
             # omit reverse_code=... if you don't want the migration to be reversible.
             migrations.RunPython(gen_uuid, reverse_code=migrations.RunPython.noop),
             migrations.AlterField(
                 model_name='mymodel',
                 name='uuid',
                 field=models.UUIDField(default=uuid.uuid4, unique=True),
             ),
         ]
* Now you can apply the migration as usual with the :djadmin:`migrate` command.

   Note there is a race condition if you allow objects to be created while this
   migration is running. Objects created after the ``AddField`` and before
   ``RunPython`` will have their original ``uuid``’s overwritten.

Answer 4

您可以手动编辑迁移文件：

我需要在某些字段中添加随机字符，因此我导入了随机和randint

import random
import string

并将默认值更改为

default=random.choice(string.lowercase)

有效。

Answer 5

有办法为South的每一行做唯一的值。

将models.py中的slug定义为：

class Foo(models.Model):
  slug = models.SlugField(unique=True, default='')
  ....

创建新迁移

运行python manage.py schemamigration --auto foo

打开新的迁移文件，然后对其进行编辑：

# Change add_column to this:
db.add_column(u'account_funnel', 'slug',
            self.gf('django.db.models.foo.Foo')(default='', 
                  unique=False,  
                  max_length=50),
            keep_default=False)

# right above this add such python code:
foos = orm['foo.Foo'].objects.all()
for foo in foos:
        foo.slug = slugify(funnel.name)
        foo.save()

# Modify slug as unique field
db.create_unique(u'foo_foo', ['slug'])

ps mark this migration as no_dry_run = True
pss do not forget to import slugify function from django.template.defaultfilters import slugify

迁移时传递South随机唯一默认值

5 个答案:

将models.py中的slug定义为：

创建新迁移

打开新的迁移文件，然后对其进行编辑：