是否有一种“最佳”方法来执行可查询的计算字段?
例如:
from django.db import models
class Person(models.Model):
given_name = models.CharField(max_length=30)
family_name = models.CharField(max_length=30)
NAME_ORDER_CONVENTION_CHOICES = (
# "Eastern" name order: family name followed by given name
('E', 'Eastern'),
# "Western" name order: given name followed by family name
('W', 'Western')
)
name_order_convention = models.CharField(
length=1,
choices=NAME_ORDER_CONVENTION_CHOICES,
)
@property
def full_name(self):
"""
Return full name, calculated on the basis of given name,
family name and name order convention.
"""
template = "{} {}"
if self.name_order_convention == "W":
return template.format(self.given_name, self.family_name)
return template.format(self.family_name, self.given_name)
这使您能够获取任何Person
的full_name
,但是如果您想根据全名进行数据库查询,则需要编写查询隐式了解如何计算此属性。这似乎违反了 DRY,因为不再有任何中心位置可以更改计算字段的计算方式 - 您必须在任何地方更改 full_name
属性它基于 full_name
工作原理的隐式知识进行查询。
我能想到的主要替代方案是重写 save()
方法以在每次更新时更新这些字段。
from django.db import models
class Person(models.Model):
given_name = models.CharField(max_length=30)
family_name = models.CharField(max_length=30)
NAME_ORDER_CONVENTION_CHOICES = (
('E', 'Eastern'),
('W', 'Western')
)
name_order_convention = models.CharField(
length=1,
choices=NAME_ORDER_CONVENTION_CHOICES,
)
# Computed fields
full_name = models.CharField(max_length=60)
def _calculate_full_name(self):
template = "{} {}"
if self.name_order_convention == "W":
self.full_name = template.format(self.given_name, self.family_name)
else:
self.full_name = template.format(self.family_name, self.given_name)
def save(self, *args, **kwargs):
self._calculate_full_name()
super(Model, self).save(*args, **kwargs)
对于我可能缺少的可查询计算字段,是否有一个通用的“最佳实践”解决方案?
最佳答案
我可以看到的一种方法:在数据库中创建 View ,并使用连接的全名而不是django中的托管模型来用于查询(Person
模型也应该存在于增删改查操作):
查看(postgresql)
CREATE OR REPLACE VIEW appname_viewperson AS
SELECT id,
given_name,
family_name,
given_name || ' ' || family_name AS full_name,
FROM appname_person
非托管模型:
class ViewPerson(models.Model):
given_name = models.CharField(max_length=30)
family_name = models.CharField(max_length=30)
full_name = models.CharField(max_length=60)
class Meta:
managed = False
关于python - Django:可查询的计算字段,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/49032297/