注意：我正在使用Django 1.9和Python 3.4.2
当我更改模型并执行迁移（./manage.py makemigrations），然后尝试应用该迁移（./manage.py migrate）时，我遇到了一个奇怪的错误。
类似的问题在这里有一个链接，但是没有答案，人们询问更多信息，评论中唯一可能的解决方案似乎是删除迁移文件并重新开始 - 但我真的很想知道是什么导致了这个问题以及如何正确地解决它。
错误信息如下：
当我更改模型并执行迁移（./manage.py makemigrations），然后尝试应用该迁移（./manage.py migrate）时，我遇到了一个奇怪的错误。
类似的问题在这里有一个链接，但是没有答案，人们询问更多信息，评论中唯一可能的解决方案似乎是删除迁移文件并重新开始 - 但我真的很想知道是什么导致了这个问题以及如何正确地解决它。
错误信息如下：
Operations to perform:
Apply all migrations: contenttypes, admin, auth, blog, sessions
Running migrations:
Rendering model states... DONE
Applying blog.0004_auto_20160103_1321...Traceback (most recent call last):
File "./manage.py", line 10, in <module>
execute_from_command_line(sys.argv)
File "/Users/owen/src/projects/owen/lib/python3.4/site-packages/django/core/management/__init__.py", line 350, in execute_from_command_line
utility.execute()
File "/Users/owen/src/projects/owen/lib/python3.4/site-packages/django/core/management/__init__.py", line 342, in execute
self.fetch_command(subcommand).run_from_argv(self.argv)
File "/Users/owen/src/projects/owen/lib/python3.4/site-packages/django/core/management/base.py", line 348, in run_from_argv
self.execute(*args, **cmd_options)
File "/Users/owen/src/projects/owen/lib/python3.4/site-packages/django/core/management/base.py", line 399, in execute
output = self.handle(*args, **options)
File "/Users/owen/src/projects/owen/lib/python3.4/site-packages/django/core/management/commands/migrate.py", line 200, in handle
executor.migrate(targets, plan, fake=fake, fake_initial=fake_initial)
File "/Users/owen/src/projects/owen/lib/python3.4/site-packages/django/db/migrations/executor.py", line 92, in migrate
self._migrate_all_forwards(plan, full_plan, fake=fake, fake_initial=fake_initial)
File "/Users/owen/src/projects/owen/lib/python3.4/site-packages/django/db/migrations/executor.py", line 121, in _migrate_all_forwards
state = self.apply_migration(state, migration, fake=fake, fake_initial=fake_initial)
File "/Users/owen/src/projects/owen/lib/python3.4/site-packages/django/db/migrations/executor.py", line 198, in apply_migration
state = migration.apply(state, schema_editor)
File "/Users/owen/src/projects/owen/lib/python3.4/site-packages/django/db/migrations/migration.py", line 123, in apply
operation.database_forwards(self.app_label, schema_editor, old_state, project_state)
File "/Users/owen/src/projects/owen/lib/python3.4/site-packages/django/db/migrations/operations/fields.py", line 201, in database_forwards
schema_editor.alter_field(from_model, from_field, to_field)
File "/Users/owen/src/projects/owen/lib/python3.4/site-packages/django/db/backends/base/schema.py", line 482, in alter_field
old_db_params, new_db_params, strict)
File "/Users/owen/src/projects/owen/lib/python3.4/site-packages/django/db/backends/base/schema.py", line 564, in _alter_field
old_default = self.effective_default(old_field)
File "/Users/owen/src/projects/owen/lib/python3.4/site-packages/django/db/backends/base/schema.py", line 210, in effective_default
default = field.get_db_prep_save(default, self.connection)
File "/Users/owen/src/projects/owen/lib/python3.4/site-packages/django/db/models/fields/__init__.py", line 728, in get_db_prep_save
prepared=False)
File "/Users/owen/src/projects/owen/lib/python3.4/site-packages/django/db/models/fields/__init__.py", line 720, in get_db_prep_value
value = self.get_prep_value(value)
File "/Users/owen/src/projects/owen/lib/python3.4/site-packages/django/db/models/fields/__init__.py", line 1112, in get_prep_value
return self.to_python(value)
File "/Users/owen/src/projects/owen/lib/python3.4/site-packages/django/db/models/fields/__init__.py", line 1108, in to_python
return smart_text(value)
File "/Users/owen/src/projects/owen/lib/python3.4/site-packages/django/utils/encoding.py", line 42, in smart_text
return force_text(s, encoding, strings_only, errors)
File "/Users/owen/src/projects/owen/lib/python3.4/site-packages/django/utils/encoding.py", line 76, in force_text
s = six.text_type(s)
File "/Users/owen/src/projects/owen/lib/python3.4/site-packages/django/db/models/fields/__init__.py", line 188, in __str__
model = self.model
AttributeError: 'CharField' object has no attribute 'model'
变更前的模型：
from django.db import models
from django.utils import timezone
class Category(models.Model):
title = models.CharField(max_length=100, unique=True)
def __str__(self):
return self.title
def number_of_articles(self):
articles = Article.objects.filter(categories__pk=self.id)
return articles.count()
class Article(models.Model):
title = models.CharField(max_length=255, unique=True)
slug = models.SlugField(max_length=255, unique=True, default=title)
pub_date = models.DateTimeField('date published', default=timezone.now)
intro_text = models.TextField(blank=True)
body_copy = models.TextField(blank=False)
votes_helpful = models.IntegerField(default=0, blank=True)
votes_unhelpful = models.IntegerField(default=0, blank=True)
categories = models.ManyToManyField(Category, blank=True)
class Meta:
ordering = ('-pub_date',)
def __str__(self):
return self.title
def has_votes(self):
total_num_votes = self.votes_helpful + self.votes_unhelpful
return total_num_votes > 0
我的模型变更：
slug = models.SlugField(max_length=255, blank=True)
修改的地方是我从 Article 中删除了 unique=True, default=title，并添加了 blank=False。
我的迁移文件:
# -*- coding: utf-8 -*-
# Generated by Django 1.9 on 2016-01-03 13:21
from __future__ import unicode_literals
from django.db import migrations, models
class Migration(migrations.Migration):
dependencies = [
('blog', '0003_auto_20151230_1643'),
]
operations = [
migrations.AlterField(
model_name='article',
name='slug',
field=models.SlugField(blank=True, max_length=255),
),
]