python - 如何在额外字段上过滤 Django 查询集？

Question

这是我的 Django 模型:

from django.db import models
class MyModel(models.Model):
    a = models.IntegerField()
    b = models.IntegerField()
    c = models.IntegerField()

我想检索此模型的所有实例，其中 a = 5 和 b + c > 10。我该怎么做？

当我尝试这样做时:

print MyModel.objects.filter(a=5).extra(
    select={"total_count": "b + c"},
    where=["total_count > 10"],
)

我收到这个错误:

OperationalError: (1054, "Unknown column 'total_count' in 'where clause'")

Answer 1

您可以将 b + c > 10 转换为 b > 10 - c 然后使用 F built-in function

MyModel.objects.filter(a=5).filter((b__gt=10-models.F('c'))

使用 Django extra() 不是很安全

You should be very careful whenever you use extra(). Every time you use it, you should escape any parameters that the user can control by using params in order to protect against SQL injection attacks . Please read more about SQL injection protection.