Finally, in Django 1.8, we have a specific method to do this. It's called refresh_from_db and it's a new method of the class django.db.models.Model.
An example of usage:
def update_result(self):
obj = MyModel.objects.create(val=1)
MyModel.objects.filter(pk=obj.pk).update(val=F('val') + 1)
# At this point obj.val is still 1, but the value in the database
# was updated to 2. The object's updated value needs to be reloaded
# from the database.
obj.refresh_from_db()
If your version of Django is less than 1.8 but you want to have this functionality, modify your model to inherit from RefreshableModel:
from django.db import models
from django.db.models.constants import LOOKUP_SEP
from django.db.models.query_utils import DeferredAttribute
class RefreshableModel(models.Model):
class Meta:
abstract = True
def get_deferred_fields(self):
"""
Returns a set containing names of deferred fields for this instance.
"""
return {
f.attname for f in self._meta.concrete_fields
if isinstance(self.__class__.__dict__.get(f.attname), DeferredAttribute)
}
def refresh_from_db(self, using=None, fields=None, **kwargs):
"""
Reloads field values from the database.
By default, the reloading happens from the database this instance was
loaded from, or by the read router if this instance wasn't loaded from
any database. The using parameter will override the default.
Fields can be used to specify which fields to reload. The fields
should be an iterable of field attnames. If fields is None, then
all non-deferred fields are reloaded.
When accessing deferred fields of an instance, the deferred loading
of the field will call this method.
"""
if fields is not None:
if len(fields) == 0:
return
if any(LOOKUP_SEP in f for f in fields):
raise ValueError(
'Found "%s" in fields argument. Relations and transforms '
'are not allowed in fields.' % LOOKUP_SEP)
db = using if using is not None else self._state.db
if self._deferred:
non_deferred_model = self._meta.proxy_for_model
else:
non_deferred_model = self.__class__
db_instance_qs = non_deferred_model._default_manager.using(db).filter(pk=self.pk)
# Use provided fields, if not set then reload all non-deferred fields.
if fields is not None:
fields = list(fields)
db_instance_qs = db_instance_qs.only(*fields)
elif self._deferred:
deferred_fields = self.get_deferred_fields()
fields = [f.attname for f in self._meta.concrete_fields
if f.attname not in deferred_fields]
db_instance_qs = db_instance_qs.only(*fields)
db_instance = db_instance_qs.get()
non_loaded_fields = db_instance.get_deferred_fields()
for field in self._meta.concrete_fields:
if field.attname in non_loaded_fields:
# This field wasn't refreshed - skip ahead.
continue
setattr(self, field.attname, getattr(db_instance, field.attname))
# Throw away stale foreign key references.
if field.rel and field.get_cache_name() in self.__dict__:
rel_instance = getattr(self, field.get_cache_name())
local_val = getattr(db_instance, field.attname)
related_val = None if rel_instance is None else getattr(rel_instance, field.related_field.attname)
if local_val != related_val:
del self.__dict__[field.get_cache_name()]
self._state.db = db_instance._state.db
class MyModel(RefreshableModel):
# Your Model implementation
pass
obj = MyModel.objects.create(val=1)
obj.refresh_from_db()
