无法使Django外键工作

我是Django的新手，但看起来这一次应该很容易。我使用的是Django 1.5 beta2，但我认为它应该足够稳定，可以用于像这样简单的事情。 以下是我在注册应用程序中的课程

class Shift(models.Model):
    begin_date = models.DateTimeField()
    finish_date = models.DateTimeField(null=True)

    def __unicode__(self):
        return str(self.begin_date) + ' to ' + str(self.end_date)

class Transaction(models.Model):
    begin_date = models.DateTimeField()
    finish_date = models.DateTimeField(null=True)
    status = models.CharField(max_length=10, default='Started')
    shift = models.ForeignKey(Shift)

    def __unicode__(self):
        return str(self.begin_date) + ' to ' + self(self.end_date)

但当我尝试创建一个子事务时，它失败了

david@fink:~/orthosie$ python manage.py shell
Python 2.7.3 (default, Sep 26 2012, 21:53:58) 
[GCC 4.7.2] on linux2
Type "help", "copyright", "credits" or "license" for more information.
(InteractiveConsole)
>>> from register.models import Shift, Transaction
>>> from django.utils import timezone
>>> s = Shift(begin_date=timezone.now())
>>> s.transaction_set.create(begin_date=timezone.now())
Traceback (most recent call last):
  File "<console>", line 1, in <module>
  File "/usr/local/lib/python2.7/dist-packages/django/db/models/fields/related.py", line 529, in create

    return super(RelatedManager, self.db_manager(db)).create(**kwargs)
  File "/usr/local/lib/python2.7/dist-packages/django/db/models/manager.py", line 149, in create
    return self.get_query_set().create(**kwargs)
  File "/usr/local/lib/python2.7/dist-packages/django/db/models/query.py", line 394, in create
    obj.save(force_insert=True, using=self.db)
  File "/usr/local/lib/python2.7/dist-packages/django/db/models/base.py", line 537, in save
    force_update=force_update, update_fields=update_fields)
  File "/usr/local/lib/python2.7/dist-packages/django/db/models/base.py", line 632, in save_base
    result = manager._insert([self], fields=fields, return_id=update_pk, using=using, raw=raw)
  File "/usr/local/lib/python2.7/dist-packages/django/db/models/manager.py", line 215, in _insert
    return insert_query(self.model, objs, fields, **kwargs)
  File "/usr/local/lib/python2.7/dist-packages/django/db/models/query.py", line 1646, in insert_query

return query.get_compiler(using=using).execute_sql(return_id)
  File "/usr/local/lib/python2.7/dist-packages/django/db/models/sql/compiler.py", line 935, in execute_sql
    cursor.execute(sql, params)
  File "/usr/local/lib/python2.7/dist-packages/django/db/backends/util.py", line 41, in execute
    return self.cursor.execute(sql, params)
  File "/usr/local/lib/python2.7/dist-packages/django/db/backends/sqlite3/base.py", line 364, in execute
    six.reraise(utils.IntegrityError, utils.IntegrityError(*tuple(e.args)), sys.exc_info()[2])
  File "/usr/local/lib/python2.7/dist-packages/django/db/backends/sqlite3/base.py", line 362, in execute
    return Database.Cursor.execute(self, query, params)
IntegrityError: register_transaction.shift_id may not be NULL
>>> 

---

我觉得我一定少了一些小东西。

s

没有id，因为它还没有保存

---

在进行调用之前调用

s.save（）

，或者使用

Shift.objects.create

而不是

Shift（）

s

没有id，因为它尚未保存

---

在进行调用之前调用

s.save（）

，或者使用

Shift.objects.create

而不是

Shift（）

我知道这将是一件愚蠢而简单的事情。非常感谢。我就知道这会是件愚蠢而简单的事。非常感谢你。

-- Describe REGISTER_TRANSACTION
CREATE TABLE "register_transaction" (
    "id" integer NOT NULL PRIMARY KEY,
    "begin_date" datetime NOT NULL,
    "finish_date" datetime,
    "status" varchar(10) NOT NULL,
    "shift_id" integer NOT NULL REFERENCES "register_shift" ("id")
)