我想获取所有代码模型对象并计算返回对象的长度 . 我收到一个我无法理解的错误 .
这是我的模特
class Codes(models.Model):
username = models.CharField(max_length=100)
code = models.CharField(max_length=10000)
language = models.CharField(max_length=100)
def __str__(self):
return self.language
我正在使用以下函数从模型中获取所有对象
def get_all_codes(lang):
queryset = Codes.objects.filter(language = lang)
return queryset
调用函数
all_codes_of_lang = get_all_codes(lang)
并尝试使用以下方法计算长度：
if len(all_codes_of_lang) > 0:
print("abc")
导致此错误：
if len(all_codes_of_lang) > 0:
File "/usr/local/lib/python2.7/site-packages/django/db/models/query.py", line 240, in __len__
self._fetch_all()
File "/usr/local/lib/python2.7/site-packages/django/db/models/query.py", line 1074, in _fetch_all
self._result_cache = list(self.iterator())
File "/usr/local/lib/python2.7/site-packages/django/db/models/query.py", line 52, in __iter__
results = compiler.execute_sql()
File "/usr/local/lib/python2.7/site-packages/django/db/models/sql/compiler.py", line 848, in execute_sql
cursor.execute(sql, params)
File "/usr/local/lib/python2.7/site-packages/django/db/backends/utils.py", line 79, in execute
return super(CursorDebugWrapper, self).execute(sql, params)
File "/usr/local/lib/python2.7/site-packages/django/db/backends/utils.py", line 64, in execute
return self.cursor.execute(sql, params)
File "/usr/local/lib/python2.7/site-packages/django/db/utils.py", line 95, in __exit__
six.reraise(dj_exc_type, dj_exc_value, traceback)
File "/usr/local/lib/python2.7/site-packages/django/db/backends/utils.py", line 64, in execute
return self.cursor.execute(sql, params)
ProgrammingError: relation "submissions_codes" does not exist
LINE 1: ...odes"."code", "submissions_codes"."language" FROM "submissio...
^
-->
2 回答
此问题不是
get_all_codes函数或计算长度，而是模型和数据库之间存在同步问题 .运行
python manage.py makemigrations和python manage.pymigrate进行修复 .模型没有迁移，这就是你遇到这个错误的原因 . 运行以下命令
python manage.py makemigrationspython manage.py migrate