Python Django:可查询的计算字段
是否有一种“最佳”方式来处理可查询的计算字段 例如:Python Django:可查询的计算字段,python,django,django-models,computed-properties,computed-field,Python,Django,Django Models,Computed Properties,Computed Field,是否有一种“最佳”方式来处理可查询的计算字段 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 or
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)
这使您能够为任何人员
获取全名
,但如果您希望基于全名执行数据库查询,则需要编写一个包含如何计算此属性的隐式知识的查询。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-您必须更改full_name
属性,以及基于full_name
工作方式的隐式知识进行查询的任何位置
我能想到的主要替代方法是重写save()
方法,以便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?我可以看到的一种方法是:在数据库中创建视图,在django中使用连接的全名和非托管模型,该模型将用于查询(
Person
模型也应存在于crud操作中):
视图(postgresql)
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
我可以看到的一种方法是:在数据库中创建视图,并使用连接的全名和django中的非托管模型,该模型将用于查询(
Person
model也应存在于crud操作中):
视图(postgresql)
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
答案可能在于django相当新的查询注释:
答案可能在于django相当新的查询注释:
company = Company.objects.annotate(
chairs_needed=F('num_employees') - F('num_chairs'))