how solve django create model class dynamically - python-3.x

Question

When dynamically creating and generating Model class, modify some
properties, fill in the information required by the sub-table, the
first time can return the normal result, the second result error,
after the analysis of the second result field to retain the first
table name:
class Object:
def __init__(self, **kwargs):
self.__dict__.update(kwargs)
def _model_new(cls, *args, **kwargs):
return cls(*args, **kwargs)enter code here
class ShardModel(object):
_shard_db_models = {}
temp_class = []
def __new__(cls, *args, **kwargs):
shard_key = kwargs.pop('shard_key', 0) % cls.Config.table_num
model_name = cls.__name__
model_name += '_%s' % shard_key
model_class = cls._shard_db_models.get(model_name)
if model_class is not None:
return model_class
# Deep copy attrs
attrs = dict()
attrs.update(cls.__dict__)
if 'objects' in attrs:
attrs['objects'] = attrs['objects'].__class__()
# Set table name with shard_key
meta = Object(**cls.Meta.__dict__)
meta.db_table = meta.db_table % shard_key
meta.abstract = False
attrs['Meta'] = meta
attrs['new'] = classmethod(_model_new)
attrs['__module__'] = cls.__name__
cursor = connection.cursor()
tables = [table_info.name for table_info in connection.introspection.get_table_list(cursor)]
# Create model class dynamically
model_class = type(model_name, tuple([models.Model] + list(cls.__bases__[1:])), attrs)
print(model_class)
if meta.db_table not in tables:
for cmd in ('makemigrations', 'migrate'):
exec_command(cmd, meta.app_label)
cls._shard_db_models[model_name] = model_class
return model_class
this is my model
class Nice(ShardModel):
user_id = models.IntegerField()
user_name = models.CharField(max_length=256)
password = models.CharField(max_length=256)
class Config:
table_num = 3
class Meta:
app_label = 'Test'
db_table = 'test_%s'
abstract = True
this my view
def NiceView(request):
user_id = int(request.GET.get('user_id'))
user = Nice(shard_key=user_id).objects.get(user_id=user_id)
return HttpResponse(json.dumps(model_to_dict(user)))
Here are the two times test results
url:http://127.0.0.1:8000/test?user_id=7
results:{"id": 2, "user_id": 7, "user_name": "ni", "password": "hao"};url:http://127.0.0.1:8000/test?user_id=5;error:(1054, "Unknown column 'test_1.user_id' in 'field list'")