Django Queryset - 获取最后一个相关对象并按其数据过滤

Question

I have two Django Models:

class Person(models.Model):
    unique_id = models.CharField()

class PersonData(models.Model):
    person = models.ForeignKey('Person')
    phone = models.CharField()
    email = models.CharField()
    date = models.DateTimeField()

New PersonData objects are added when their information changes, but old ones are kept. And then I want to have a filter, which will filter persons by their data from the latest PersonData object they are related to.

I have the following queryset:

filter_email = "email@example.com"
filter_phone = "964477425"

qs = Person.objects.all()

if filter_email:
    qs = qs.filter(persondata__email__icontains=filter_email)
if filter_phone:
    qs = qs.filter(persondata__phone__icontains=filter_phone)

But that filter searches through every PersonData object associated with Person . Is it possible to restrict this filter to only the latest PersonData object?

Answer 1

It is a popular type of query where latest/oldest entry against unique values of one field are desired.

I would like to say that if you think over what other answers suggest deeply, you'll understand they do not serve the purpose.

There is no way to fetch the whole object with desired filter in single django query ( Note that it is possible to get one field but not all fields, also it is possible to fetch all fields in raw **sql** queries ).

One of the ways I know to tackle this problem is to have a foreign-key in Person to the latest PersonData object, and update it each time new object of PersonData is created.

Answer 2

So you could try query to PersonData model:

qs = PersonData.objects.filter()

if filter_email:
    qs = PersonData.objects.filter(email__icontains=filter_email)
if filter_phone:
    qs = PersonData.objects.filter(phone__icontains=filter_phone)

# Cache Person object and pick the last
qs = qs.select_related('person').last()