How to create a Django queryset from a list of values

Question

I am given a list like so

a = [1, 2, 3, 4]

This list matches the id’s stored in a django model we will call Books.

I am trying to return a queryset of Books with the id’s in the list. I am thinking of using Q objects and grab them by doing something like this

Books.objects.filter(Q(id = 1) | Q(id=2) | Q(id=3) | Q(id=4))

Now i would just use the index like this:

Books.objects.filter(Q(id = a[0]) | Q(id=a[1]) | Q(id=a[2]) | Q(id=a[3]))

BUT, These list will be varying in length up to around 30 and hardcoding the index wont work, and hardcoding the query won’t satisfy the varying length of lists.

Is it possible to go this route? And if so, how can I accomplish returning the books with the id’s that match the list?

Asked By: Mfreeman

||

Source

Answer 1

You should use the __in lookup [Django-doc] here:

Books.objects.filter(pk__in=a)

As the documentation says:

In a given iterable; often a list, tuple, or queryset. It’s not a common use case, but strings (being iterables) are accepted.

Answered By: Willem Van Onsem

Answer 2

For a simple case, use __in lookup as per the answer above

However, Q objects connected with | is not magic syntax, so it ought to be possible to build chains of them using loops, like

qlst = []
for x in some_iterable
    qel = Q( something based on x)
    qlst.append(qel)
if len(qlst) == 0:
    # oops -- must handle somehow, or code below will crash
filter = qlst[0]
for qel in qlst[1:]:
    filter = filter | qel

queryset = Books.objects.filter( filter)

Caveat: I’ve never actually needed to try this.

Answered By: nigel222

Answer 3

Work: this Working for me very help full this …
i have dynamic list and this code very easy my w

Answered By: dark army

How to create a Django queryset from a list of values

Question:

Answers: