这是我的好函数:
def is_serviceable(address):
"""
Checks if an address can be serviced by an Employee.
Returns True if address' lat-lng intersects with any of Employees' coverage.
If it doesn't, but address' locality is listed in world District model,
returns False and locality name.
Just returns False if nothing found.
-- address -- django-address Address object. Address should be geocoded (i.e
have latitude and longitude fields correctly filled)
"""
pnt = Point(address.longitude, address.latitude)
employee_exists = Employee.objects.filter(coverage__mpoly__intersects=pnt).exists()
district = District.objects.filter(mpoly__intersects=pnt).first()
if (employee_exists):
return employee_exists
elif district:
return False, district.name
else:
return False
为了获得我想要的结果，我必须执行两个数据库查询，首先查询 Employee 表，然后查询 District 表。这似乎不是一种可扩展的方法。但是，由于Employee的coverage属性实际上是与District模型的多对多关系字段:
class Employee(models.Model):
coverage = models.ManyToManyField(
District,
related_name="employees",
verbose_name=_("assigned districts")
)
class District(models.Model):
mpoly = models.MultiPolygonField()
...我很确定有一种方法可以将查询压缩到一个查询集中，或者，如果 Django ORM 不适合这种情况，则可以压缩到单个 SQL 语句。
不过，我不知道从哪里开始挖掘。有什么想法吗？
编辑:由于 Django 的注释功能而解决。
请您参考如下方法:
员工对象可以访问其相关的 District 对象:
x=Employee.objects.all()[0]
print x.district_set.all()
