我有以下模型：
class Work(models.Model):
title = models.CharField(max_length=30)
amount = models.PositiveIntegerField()
percent = models.FloatField(validators=[MaxValueValidator
(100),MinValueValidator(0)])
drop = models.PositiveIntegerField(default=0)
assignments = models.ManyToManyField(Assignment)
但是当我创建一些“工作”时，它的行为很奇怪：
In [6]: homework = Work("homework",12,15)
In [7]: homework.save()
---------------------------------------------------------------------------
ValueError Traceback (most recent call last)
...
#lots and lots of stuff...I will post the extend at the bottom
...
ValueError: invalid literal for int() with base 10: 'homework'
当第一个参数需要 CharField 时，为什么读取第一个参数应该是 int？
我觉得我说的很有道理。homework.title应该是“作业”，homework.amount应该是 12，homework.percent应该是 15，并且homework.drop应该是默认值：0。
有人可以解释为什么会出现此错误以及如何修复它。提前致谢。
完整的错误结果：
In [6]: homework = Work("homework",12,15)
In [7]: homework.save()
---------------------------------------------------------------------------
ValueError Traceback (most recent call last)
/opt/local/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site-packages/django/core/management/commands/shell.pyc in <module>()
----> 1 homework.save()
/opt/local/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site-packages/django/db/models/base.pyc in save(self, force_insert, force_update, using, update_fields)
544
545 self.save_base(using=using, force_insert=force_insert,
--> 546 force_update=force_update, update_fields=update_fields)
547 save.alters_data = True
548
/opt/local/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site-packages/django/db/models/base.pyc in save_base(self, raw, cls, origin, force_insert, force_update, using, update_fields)
620 # no force_insert)
621 if ((force_update or update_fields) or (not force_insert and
--> 622 manager.using(using).filter(pk=pk_val).exists())):
623 if force_update or non_pks:
624 values = [(f, None, (raw and getattr(self, f.attname) or f.pre_save(self, False))) for f in non_pks]
/opt/local/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site-packages/django/db/models/query.pyc in filter(self, *args, **kwargs)
665 set.
666 """
--> 667 return self._filter_or_exclude(False, *args, **kwargs)
668
669 def exclude(self, *args, **kwargs):
/opt/local/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site-packages/django/db/models/query.pyc in _filter_or_exclude(self, negate, *args, **kwargs)
683 clone.query.add_q(~Q(*args, **kwargs))
684 else:
--> 685 clone.query.add_q(Q(*args, **kwargs))
686 return clone
687
/opt/local/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site-packages/django/db/models/sql/query.pyc in add_q(self, q_object, used_aliases, force_having)
1257 else:
1258 self.add_filter(child, connector, q_object.negated,
-> 1259 can_reuse=used_aliases, force_having=force_having)
1260 if force_having:
1261 self.having.end_subtree()
/opt/local/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site-packages/django/db/models/sql/query.pyc in add_filter(self, filter_expr, connector, negate, trim, can_reuse, process_extras, force_having)
1188 else:
1189 self.where.add((Constraint(alias, col, field), lookup_type, value),
-> 1190 connector)
1191
1192 if negate:
/opt/local/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site-packages/django/db/models/sql/where.pyc in add(self, data, connector)
69
70 if hasattr(obj, "prepare"):
---> 71 value = obj.prepare(lookup_type, value)
72
73 super(WhereNode, self).add(
/opt/local/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site-packages/django/db/models/sql/where.pyc in prepare(self, lookup_type, value)
337 def prepare(self, lookup_type, value):
338 if self.field:
--> 339 return self.field.get_prep_lookup(lookup_type, value)
340 return value
341
/opt/local/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site-packages/django/db/models/fields/__init__.pyc in get_prep_lookup(self, lookup_type, value)
320 return value
321 elif lookup_type in ('exact', 'gt', 'gte', 'lt', 'lte'):
--> 322 return self.get_prep_value(value)
323 elif lookup_type in ('range', 'in'):
324 return [self.get_prep_value(v) for v in value]
/opt/local/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site-packages/django/db/models/fields/__init__.pyc in get_prep_value(self, value)
553 if value is None:
554 return None
--> 555 return int(value)
556
557 def contribute_to_class(self, cls, name):
ValueError: invalid literal for int() with base 10: 'homework'