Get several unique fields values in django - django

Question

I have a model:
class MyModel(models.Model):
a = models.CharField(...)
b = models.CharField(...)
And some substring "substring"
To get all unique values from fields a and b which contains those substring I can do that:
a_values = MyModel.objects.filter(a__icontains=substring).values_list("a", flat=True).distinct()
b_values = MyModel.objects.filter(b__icontains=substring).values_list("b", flat=True).distinct()
unique_values = list(set([*a_values, *b_values]))
Is it possible to rewrite it with one database request?
PS to clarify
from objects:
MyModel(a="x", b="y")
MyModel(a="xx", b="xxx")
MyModel(a="z", b="xxxx")
by substring "x" I expect to get:
unique_values = ["x", "xx", "xxx", "xxxx"]

Answer 1

You can here make a union of two queries that are never evaluated individually, like:
qa = MyModel.objects.filter(a__icontains=query).values_list('a', flat=True)
qb = MyModel.objects.filter(b__icontains=query).values_list('b', flat=True)
result = list(qa.union(qb))
Since qa and qb are lazy querysets, we never evaluate these. The query that will be performed is:
(
SELECT mymodel.a
FROM mymodel
WHERE mymodel.a LIKE %query%
)
UNION
(
SELECT mymodel.b
FROM mymodel
WHERE mymodel.b
LIKE %query%
)
The union furthermore will only select distinct values. Even if a value occurs both in a and in b, it will only be retrieved once.
For example:
>>> MyModel(a="x", b="y").save()
>>> MyModel(a="xx", b="xxx").save()
>>> MyModel(a="z", b="xxxx").save()
>>> query = 'x'
>>> qa = MyModel.objects.filter(a__icontains=query).values_list('a', flat=True)
>>> qb = MyModel.objects.filter(b__icontains=query).values_list('b', flat=True)
>>> list(qa.union(qb))
['x', 'xx', 'xxx', 'xxxx']

Answer 2

why not get both of them in the values and then flatten the list ?
unique_values = MyModel.objects.filter(
Q(a__icontains=substring) | Q(b__icontains=substring)
).values_list("a", "b").distinct()
unique_values = sum(unqiue_values, [])
if sum doesnt work here, then you can probably use flatten from itertools. Sum won't probably work because we getting a list of tuples instead of list of lists. Sorry i couldn't test this right now.