[英]How to create an alias for Django Model field?
My Django Model has a datetime field named 'updatedOn', I need to use a library function on this model to calculate some statistics, but the function assumes the datetime field name to be 'time', here is how the function uses the datetime: 我的Django模型有一个名为'updatedOn'的日期时间字段,我需要在此模型上使用库函数来计算一些统计信息,但该函数假定日期时间字段名称为'时间',这是函数使用日期时间的方式:
c = qset.filter(time__year=tt.year, time__month=tt.month, time__day=tt.day).count();
Without touching the library code, how can I create an alias 'time' to refer to 'updatedOn' field, so that I can use the function? 在不触及库代码的情况下,如何创建别名'time'来引用'updatedOn'字段,以便我可以使用该函数?
I haven't looked into this very deeply, but intuitively, some of the following ways might get you started. 我没有深入研究过这个问题,但直观地说,以下一些方法可能会让你开始。
A custom manager with a modified get_queryset
method to look for updatedOn
when filtering for time
. 具有修改的
get_queryset
方法的自定义管理器 ,用于在过滤time
时查找updatedOn
。
It might be possible to create a custom field type which only acts as a reference to another field. 可以创建自定义字段类型 ,该类型仅用作对另一个字段的引用。
The model object's _meta.fields
seems to contain the list of fields in that object. 模型对象的
_meta.fields
似乎包含该对象中的字段列表。 Maybe you could try adding some kind of dummy field called time
, which refers to the updatedOn
field. 也许你可以尝试添加一种称为
time
的虚拟字段,它指的是updatedOn
字段。
This old Django Snippet , worked for me, until Django 1.11. 这个老Django Snippet ,为我工作,直到Django 1.11。 As @Jaberwocky commented
virtual_only
gets removed in Django 2.0 正如@Jaberwocky评论的那样,在Django 2.0中删除了
virtual_only
However, the deprecation warning reads that this field is deprecated in favor of private_only
, although this is not mentioned in the features removed of the above link. 但是, 弃用警告会读取此字段已弃用而不支持
private_only
,尽管在上述链接中删除的功能中未提及此字段。
class AliasField(models.Field):
# def contribute_to_class(self, cls, name, virtual_only=False):
# '''
# virtual_only is deprecated in favor of private_only
# '''
# super(AliasField, self).contribute_to_class(cls, name, virtual_only=True)
# setattr(cls, name, self)
def contribute_to_class(self, cls, name, private_only=False):
'''
virtual_only is deprecated in favor of private_only
'''
super(AliasField, self).contribute_to_class(cls, name, private_only=True)
setattr(cls, name, self)
def __get__(self, instance, instance_type=None):
return getattr(instance, self.db_column)
class Order(models.Model):
"""
The main order model
"""
number = AliasField(db_column='id')
Create a property for the field in your model: 为模型中的字段创建属性:
class MyModel(moels.Model):
updated_on = models.DateTimeField()
def _get_time(self):
return self.updated_on
time = property(_get_time)
following miikkas's suggestion re model.Manager, I came up with the following that works for the much simpler case of retrieving the id field by querying uuid. 遵循miikkas的建议re model.Manager,我提出了以下内容,它适用于通过查询uuid来检索id字段的更简单的情况。 the database was created with the ID being a varchar field used for a hexadecimal string, and I'm retrofitting a sequential integer ID field so I can use Django's auth module which requires it.
创建数据库的ID是一个用于十六进制字符串的varchar字段,我正在改进一个顺序整数ID字段,所以我可以使用需要它的Django的auth模块。 and I want to do this in steps, hence the hack.
我想分步进行,因此黑客攻击。
if DEVELOPMENT['merging_to_sequential_ids_incomplete']:
class ModelManager(models.Manager):
def get(self, *args, **kwargs):
if 'uuid' in kwargs:
kwargs['id'] = kwargs.pop('uuid')
return super(ModelManager, self).get(*args, **kwargs)
class Model(models.Model):
if DEVELOPMENT['merging_to_sequential_ids_incomplete']:
print >>sys.stderr, 'WARNING: uuid now a synonym to id'
id = models.CharField(max_length = 32,
primary_key = True, default = uuid_string)
objects = ModelManager() # for Client.objects.get(uuid=...)
uuid = property(lambda self: self.id) # for client.uuid
else:
id = models.AutoField(primary_key = True)
uuid = models.CharField(max_length = 32, ...
now I can: 现在我能:
cd myapp && ../djangopython manage.py shell
WARNING: uuid now a synonym to id
setting up special admin settings
Python 2.7.8 (default, Nov 18 2014, 16:29:10)
[GCC 4.9.2] on linux2
Type "help", "copyright", "credits" or "license" for more information.
(InteractiveConsole)
>>> from myapp.models import *
>>> Client.objects.get(uuid=u'18b86bd7b58e4c0186f7654045ce81d9')
<Client: jc@example.net>
>>> _.uuid
u'18b86bd7b58e4c0186f7654045ce81d9'
filter
could be done the same way. filter
可以以相同的方式完成。
maybe this can help guide someone else looking for a way to use an "alias" or "synonym" for a Django model field. 也许这可以帮助指导其他人寻找一种方法来为Django模型字段使用“别名”或“同义词”。 I don't believe it will help the OP though.
我不相信它会对OP有所帮助。 the custom field type might be the better general approach.
自定义字段类型可能是更好的通用方法。
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