Django qs1.difference(qs2, qs3) not supported by backend

问题

I need to check a table from a remote db and update another table in my db. The models have same fields but checking with difference method will return an error:

qs1 get the data from one postgresql db

qs2 get the data from one mysql db

qs1 = (Local.objects
            .values_list('ref')
)
qs2 = (Remote.objects
            .filter()
            .values_list('ref'))

>>> qs1.difference(qs1, qs2)

DatabaseError: intersection not supported on this database backend.

回答1:

I'm not exactly sure what you think your code is doind.

qs1 looks for a model Local in your default Databasengine. And qs2 looks for a model Remote also in your default Databasengine.

What you might want to do is defining a second Database in your settings.py naming it for Instance "remote" and then modify your q2 as follows :

qs2 = (Remote.objects.using("remote").filter().values_list('ref'))

This tells django that it shall contact your remote Database not your Local one.

Lemme know wether this helps or not.

回答2:

check = Qs1.objects.all()
prg=[]
[prg.append(x.ref) for x in check]
difference = (Qs2.objects
        .exclude(ref__in=prg)
        .values()
)

Maybe it's not elegant, but it just works.

来源：https://stackoverflow.com/questions/47282190/django-qs1-differenceqs2-qs3-not-supported-by-backend