在我的模型中我有:
class Alias(MyBaseModel):
remote_image = models.URLField(
max_length=500, null=True,
help_text='''
A URL that is downloaded and cached for the image.
Only used when the alias is made
'''
)
image = models.ImageField(
upload_to='alias', default='alias-default.png',
help_text="An image representing the alias"
)
def save(self, *args, **kw):
if (not self.image or self.image.name == 'alias-default.png') and self.remote_image :
try :
data = utils.fetch(self.remote_image)
image = StringIO.StringIO(data)
image = Image.open(image)
buf = StringIO.StringIO()
image.save(buf, format='PNG')
self.image.save(
hashlib.md5(self.string_id).hexdigest() + ".png", ContentFile(buf.getvalue())
)
except IOError :
pass
这在remote_image第一次改变的时候工作得很好。
当有人修改了别名上的remote_image时，我如何获取一个新的图像?其次，是否有更好的方法来缓存远程映像?
修改@ivanperelivskiy的回答:
@property
def _dict(self):
ret = {}
for field in self._meta.get_fields():
if isinstance(field, ForeignObjectRel):
# foreign objects might not have corresponding objects in the database.
if hasattr(self, field.get_accessor_name()):
ret[field.get_accessor_name()] = getattr(self, field.get_accessor_name())
else:
ret[field.get_accessor_name()] = None
else:
ret[field.attname] = getattr(self, field.attname)
return ret
这里使用了django 1.10的公共方法get_fields。这使得代码更经得起未来的考验，但更重要的是还包括了外键和edititable =False的字段。
作为参考，这里是.fields的实现
@cached_property
def fields(self):
"""
Returns a list of all forward fields on the model and its parents,
excluding ManyToManyFields.
Private API intended only to be used by Django itself; get_fields()
combined with filtering of field properties is the public API for
obtaining this field list.
"""
# For legacy reasons, the fields property should only contain forward
# fields that are not private or with a m2m cardinality. Therefore we
# pass these three filters as filters to the generator.
# The third lambda is a longwinded way of checking f.related_model - we don't
# use that property directly because related_model is a cached property,
# and all the models may not have been loaded yet; we don't want to cache
# the string reference to the related_model.
def is_not_an_m2m_field(f):
return not (f.is_relation and f.many_to_many)
def is_not_a_generic_relation(f):
return not (f.is_relation and f.one_to_many)
def is_not_a_generic_foreign_key(f):
return not (
f.is_relation and f.many_to_one and not (hasattr(f.remote_field, 'model') and f.remote_field.model)
)
return make_immutable_fields_list(
"fields",
(f for f in self._get_fields(reverse=False)
if is_not_an_m2m_field(f) and is_not_a_generic_relation(f) and is_not_a_generic_foreign_key(f))
)
改进所有领域的@josh答案:
class Person(models.Model):
name = models.CharField()
def __init__(self, *args, **kwargs):
super(Person, self).__init__(*args, **kwargs)
self._original_fields = dict([(field.attname, getattr(self, field.attname))
for field in self._meta.local_fields if not isinstance(field, models.ForeignKey)])
def save(self, *args, **kwargs):
if self.id:
for field in self._meta.local_fields:
if not isinstance(field, models.ForeignKey) and\
self._original_fields[field.name] != getattr(self, field.name):
# Do Something
super(Person, self).save(*args, **kwargs)
澄清一下，getattr的工作是获取像person.name这样带字符串的字段(即getattr(person， "name"))
这是另一种方法。
class Parameter(models.Model):
def __init__(self, *args, **kwargs):
super(Parameter, self).__init__(*args, **kwargs)
self.__original_value = self.value
def clean(self,*args,**kwargs):
if self.__original_value == self.value:
print("igual")
else:
print("distinto")
def save(self,*args,**kwargs):
self.full_clean()
return super(Parameter, self).save(*args, **kwargs)
self.__original_value = self.value
key = models.CharField(max_length=24, db_index=True, unique=True)
value = models.CharField(max_length=128)
根据文档:验证对象
full_clean()执行的第二步是调用Model.clean()。应该重写此方法，以便在模型上执行自定义验证。
此方法应用于提供自定义模型验证，并根据需要修改模型上的属性。例如，你可以使用它来自动为一个字段提供一个值，或者进行验证，需要访问多个字段:
