[Fixed]-Always True Q object

by

19👍

✅

Here’s one way to get an always true Q object:

always_true = ~Q(pk__in=[])

The ORM optimizer recognises that Q(pk__in=[]) always evaluates to False, and the ~ negates it to make it True.

👤Flimm

4👍

as Alasdair answered in comment:

Obj.filter(
    Q(some_f1=some_v1) if some else Q(), 
    f1=v1,
    f2=v2,
    f3=v3,
    f4=v4,
    ...
)
👤Ivan Borshchov

3👍

Try this;

conditions = {'f1':f1,'f2':f2, 'f3':f3}
if some:
    conditions['some_f1'] = some_v1

Obj.objects.filter(**conditions)
👤Geo Jacob

1👍

Based on this answer we can make conditional argument passing

Obj.filter(
    *( (Q(some_f1=some_v1),) if some  else ()),    
    f1=v1,
    f2=v2,
    f3=v3,
    f4=v4,
    ...
)

So, if some is True we add tuple (Q(some_f1=some_v1),) to arguments list, in other case we add empty tuple (), also we need to wrap it in *(), as always when we passing tuple of non-keyword args

👤Ivan Borshchov

1👍

An “always true” Q object is equivalent to No Q object when using AND (basic filter syntax; i.e. x and True == x), thus a DRYer alternative for your use case is as follows:

filters = dict(f1=v1,
               f2=v2,
               f3=v3,
               f4=v4,
               ...)
if some:
    filters['some_f1'] = some_v1

qs = obj.filter(**filters)

Modify according to your needs.

👤DylanYoung

0👍

Since QuerySets are lazy, you can create the default filter, and then add others base on your conditions. Django won’t run the query until the QuerySet is evaluated (for example, iterating through it in a for loop)

filtered_objects = Obj.filter(
    some_f1=some_v1,
    f1=v1,
    f2=v2,
    f3=v3,
    f4=v4,
    ...
)
if some:
    filtered_objects.filter(some_f1=some_v1)
👤dnaranjo

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