python - django.db.utils.IntegrityError : (1062, "Duplicate entry ' ' 键 'slug' ")

Question

我正在尝试遵循 tangowithdjango 这本书，并且必须添加一个 slug 来更新类别表。但是，我在尝试迁移数据库后遇到错误。

http://www.tangowithdjango.com/book17/chapters/models_templates.html#creating-a-details-page

我没有为 slug 提供默认值，所以 Django 要求我提供一个默认值，并按照书上的指示输入 ''。

值得注意的是，我没有像原书中那样使用 sqlite，而是使用 mysql。

models.py
from django.db import models
from django.template.defaultfilters import slugify

# Create your models here.
class Category(models.Model):
      name = models.CharField(max_length=128, unique=True)
      views = models.IntegerField(default=0)
      likes = models.IntegerField(default=0)
      slug = models.SlugField(unique=True)

      def save(self, *args, **kwargs):
              self.slug = slugify(self.name)
              super(Category, self).save(*args, **kwargs)

       class Meta:
              verbose_name_plural = "Categories"

       def __unicode__(self):
              return self.name

class Page(models.Model):
        category = models.ForeignKey(Category)
        title = models.CharField(max_length=128)
        url = models.URLField()
        views = models.IntegerField(default=0)

        def __unicode__(self):
                return self.title

命令提示符

sudo python manage.py migrate       
Operations to perform:
   Apply all migrations: admin, rango, contenttypes, auth, sessions
Running migrations:
  Applying rango.0003_category_slug...Traceback (most recent call last):
  File "manage.py", line 10, in <module>
    execute_from_command_line(sys.argv)
  File "/usr/local/lib/python2.7/dist-packages/django/core/management/__init__.py", line 385, in  execute_from_command_line
utility.execute()
 File "/usr/local/lib/python2.7/dist-packages/django/core/management/__init__.py", line 377, in execute
self.fetch_command(subcommand).run_from_argv(self.argv)
  File "/usr/local/lib/python2.7/dist-packages/django/core/management/base.py", line 288, in run_from_argv
self.execute(*args, **options.__dict__)
  File "/usr/local/lib/python2.7/dist-packages/django/core/management/base.py", line 338, in execute
output = self.handle(*args, **options)
  File "/usr/local/lib/python2.7/dist-packages/django/core/management/commands/migrate.py", line 160, in handle
executor.migrate(targets, plan, fake=options.get("fake", False))
  File "/usr/local/lib/python2.7/dist-packages/django/db/migrations/executor.py", line 63, in migrate
self.apply_migration(migration, fake=fake)
  File "/usr/local/lib/python2.7/dist-packages/django/db/migrations/executor.py", line 97, in apply_migration
migration.apply(project_state, schema_editor)
  File "/usr/local/lib/python2.7/dist-packages/django/db/migrations/migration.py", line 107, in apply
operation.database_forwards(self.app_label, schema_editor, project_state, new_state)
  File "/usr/local/lib/python2.7/dist-packages/django/db/migrations/operations/fields.py", line 37, in database_forwards
field,
  File "/usr/local/lib/python2.7/dist-packages/django/db/backends/mysql/schema.py", line 42, in add_field
super(DatabaseSchemaEditor, self).add_field(model, field)
  File "/usr/local/lib/python2.7/dist-packages/django/db/backends/schema.py", line 411, in add_field
self.execute(sql, params)
  File "/usr/local/lib/python2.7/dist-packages/django/db/backends/schema.py", line 98, in execute
cursor.execute(sql, params)
  File "/usr/local/lib/python2.7/dist-packages/django/db/backends/utils.py", line 81, in execute
return super(CursorDebugWrapper, self).execute(sql, params)
  File "/usr/local/lib/python2.7/dist-packages/django/db/backends/utils.py", line 65, in execute
return self.cursor.execute(sql, params)
  File "/usr/local/lib/python2.7/dist-packages/django/db/utils.py", line 94, in __exit__
six.reraise(dj_exc_type, dj_exc_value, traceback)
  File "/usr/local/lib/python2.7/dist-packages/django/db/backends/utils.py", line 65, in execute
return self.cursor.execute(sql, params)
  File "/usr/local/lib/python2.7/dist-packages/django/db/backends/mysql/base.py", line 128, in execute
return self.cursor.execute(query, args)
  File "/usr/local/lib/python2.7/dist-packages/MySQLdb/cursors.py", line 205, in execute
self.errorhandler(self, exc, value)
  File "/usr/local/lib/python2.7/dist-packages/MySQLdb/connections.py", line 36, in defaulterrorhandler
raise errorclass, errorvalue
django.db.utils.IntegrityError: (1062, "Duplicate entry '' for key 'slug'")

Answer 1

我们一步步来分析:

1. 您正在添加 slug字段 unique = True , 即:每条记录必须有不同的值， slug 中不能有两条记录具有相同的值
2. 您正在创建迁移:django 要求您为数据库中已存在的字段提供默认值，因此您提供了 ''(空字符串)作为该值。
3. 现在 django 正在尝试迁移您的数据库。在数据库中我们至少有 2 条记录
4. 迁移了第一条记录，slug 列填充了空字符串。这很好，因为 slug 中没有其他记录有空字符串领域
5. 迁移了第二条记录，slug 列填充了空字符串。那失败了，因为第一个记录在 slug 中已经有空字符串 field 。引发异常并中止迁移。

这就是您的迁移失败的原因。你应该做的就是编辑迁移，复制migrations.AlterField操作两次，在第一次操作中删除 unique=True。在这些操作之间你应该放 migrations.RunPython操作并为其提供 2 个参数:generate_slugs和 migrations.RunPython.noop .

现在您必须在迁移类之前在迁移函数中创建，将该函数命名为 generate_slugs .函数应采用 2 个参数:apps和 schema_editor .在你的函数放在第一行:

Category = apps.get_model('your_app_name', 'Category')

现在使用 Category.objects.all()循环所有记录并为每个记录提供唯一的 slug。