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问题描述

我正在使用Django应用程序的Postgres,我想进行模型更改,重置一行,因此它不再是主键。



这是我在Django目前看起来像我的模型:

  class Meeting(TimeStampedModel):
row = models.CharField(max_length = 20,primary_key = True)
total_items = models.IntegerField()

我已经运行 django-admin.py flush 以从数据库中删除所有数据。如果我运行 python manage.py makemigrations 我看到没有检测到变化。所以我们从一个干净的基地开始。



现在我在models.py中编辑,所以它不再主键:

  row = models.CharField(max_length = 20)
/ pre>

并运行 python manage.py makemigrations 并设置 1 作为默认值:

 您正在尝试添加一个不可为空的字段'id'默认;我们不能这样做(数据库需要填充现有行的东西)。 
请选择一个修复:
1)现在提供一次性默认(将在所有现有行上设置)
2)退出,并让我在models.py $中添加一个默认值b $ b选择一个选项:1
请现在输入默认值作为有效的Python
可以使用datetime和django.utils.timezone模块,因此您可以timezone.now()
>>> 1
'frontend'的迁移:
0007_auto_20150305_1129.py:
- 添加字段ID以满足
- 在会议上更改字段行

似乎运行正常。然后,如果我运行 python manage.py migrate

  $ python manage .py migrate 
要执行的操作:
同步未迁移的应用程序:debug_toolbar
应用所有迁移:contenttypes,前端,站点,auth,会话
不迁移同步应用程序:
创建表...
安装自定义SQL ...
安装索引...
运行迁移:
应用frontend.0007_auto_20150305_1129 ...追溯(最近的呼叫最后):
文件manage.py,第10行,在< module>
execute_from_command_line(sys.argv)
文件/Users/me/.virtualenvs/meetings/lib/python2.7/site-packages/django/core/management/__init__.py,第385行,在execute_from_command_line
utility.execute()
...
文件/Users/me/.virtualenvs/meetings/lib/python2.7/site-packages/django/db/backends/ utils.py,第65行,执行
return self.cursor.execute(sql,params)
django.db.utils.ProgrammingError:为表frontend_meeting的id列指定了多个默认值

为什么告诉我我有多个默认值



我需要设置一个唯一的主键值作为默认值 - 如果是,我该怎么做?



这是迁移文件的样子:

  class Migration(migrations.Migration):

依赖关系= [
('frontend','0006_auto_20150305_1050'),
]

operations = [
migrations.AddField(
model_name ='meeting',
name ='id',
field = models.AutoField(auto_created = True,primary_key = True,default = 1,serialize = False, verbose_name ='ID'),
preserve_default = False,
),
migrations.AlterField(
model_name ='meeting',
name ='row',
field = models.CharField(max_length = 20),
preserve_default = True,
),
]


解决方案

尝试使用中间迁移来实现:



1)添加 id = models.IntegerField()到你的模型。
运行 makemigrations ,然后迁移



2)从行中删除primary_key = True -field,并删除'id'字段。再次运行 makemigrations 迁移


I am working with Postgres on a Django app and I want to make a model change, resetting a row so it is no longer the primary key.

This is what my model currently looks like in Django:

class Meeting(TimeStampedModel):
    row = models.CharField(max_length=20, primary_key=True)
    total_items = models.IntegerField()

I have run django-admin.py flush to remove all data from the database. If I run python manage.py makemigrations I see No changes detected. So we are starting from a clean base.

Now I edit row in models.py so it is no longer the primary key:

row = models.CharField(max_length=20)

And run python manage.py makemigrations and set 1 as the default when asked:

You are trying to add a non-nullable field 'id' to meeting without a default; we can't do that (the database needs something to populate existing rows).
Please select a fix:
 1) Provide a one-off default now (will be set on all existing rows)
 2) Quit, and let me add a default in models.py
Select an option: 1
Please enter the default value now, as valid Python
The datetime and django.utils.timezone modules are available, so you can do e.g. timezone.now()
>>> 1
Migrations for 'frontend':
  0007_auto_20150305_1129.py:
    - Add field id to meeting
    - Alter field row on meeting

That seems to run OK. Then if I run python manage.py migrate:

$ python manage.py migrate
Operations to perform:
  Synchronize unmigrated apps: debug_toolbar
  Apply all migrations: contenttypes, frontend, sites, auth, sessions
Synchronizing apps without migrations:
  Creating tables...
  Installing custom SQL...
  Installing indexes...
Running migrations:
  Applying frontend.0007_auto_20150305_1129...Traceback (most recent call last):
  File "manage.py", line 10, in <module>
    execute_from_command_line(sys.argv)
  File "/Users/me/.virtualenvs/meetings/lib/python2.7/site-packages/django/core/management/__init__.py", line 385, in execute_from_command_line
    utility.execute()
  ...
  File "/Users/me/.virtualenvs/meetings/lib/python2.7/site-packages/django/db/backends/utils.py", line 65, in execute
    return self.cursor.execute(sql, params)
django.db.utils.ProgrammingError: multiple default values specified for column "id" of table "frontend_meeting"

Why is it telling me I have multiple default values?

Do I need to set a unique primary key value as a default - and if so, how can I do this?

This is what the migrations file looks like:

class Migration(migrations.Migration):

    dependencies = [
        ('frontend', '0006_auto_20150305_1050'),
    ]

    operations = [
        migrations.AddField(
            model_name='meeting',
            name='id',
            field=models.AutoField(auto_created=True, primary_key=True, default=1, serialize=False, verbose_name='ID'),
            preserve_default=False,
        ),
        migrations.AlterField(
            model_name='meeting',
            name='row',
            field=models.CharField(max_length=20),
            preserve_default=True,
        ),
    ]
解决方案

Try to use an intermediate migration to achieve this:

1) Add id = models.IntegerField() to your model.Run makemigrations and then migrate.

2) Remove primary_key=True from the 'row'-field, and also remove the 'id'-field. Again run makemigrations and migrate.

这篇关于Django迁移:使行不是主键,获取“ProgrammingError:多个默认值”?的文章就介绍到这了,希望我们推荐的答案对大家有所帮助,也希望大家多多支持!

08-14 03:24