How to generate a combined Q object from a list?

Question

I have a list of dictionaries with app_label and model keys that I got from the ContentType model:

model_list = [
    {
        'app_label': 'store',
        'model': 'product',
    },
    {
        'app_label': 'store',
        'model': 'profile',
    },
]

I need to generate a set of combined Q objects from this to use as a ForeignKey.limit_choices_to argument. This is the output I need:

limit = Q(app_label = 'store', model = 'product') | Q(app_label = 'store', model = 'profile')

So I can use it in a model like this:

class Review(models.Model):
    content_type = models.ForeignKey(ContentType, limit_choices_to = limit)
    object_id = models.PositiveIntegerField()
    content_object = generic.GenericForeignKey('content_type', 'object_id')
    # ...

Anyone know how to create a list of combined Q objects with the | operator by looping through this list of dictionaries?

score 1 · Accepted Answer · answered Jan 13 '15 at 15:08

1

Using reduce with operator.or_ (or lambda a, b: a | b):

limit = reduce(operator.or_, (Q(**condition) for condition in model_list))

answered Jan 13 '15 at 15:08

falsetru

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Why can't we use `|` instead of `operator.or_`? – Anshul Goyal Jan 13 '15 at 15:11
1

@mu無, `|` requires operands (It's an oeprator, not a function like `oeprator.or_`). You need to wrap it in a `lambda` to use it. – falsetru Jan 13 '15 at 15:17
@mu無, In other word, you can't pass an operator without calling it while you can pass functions without calling it – falsetru Jan 13 '15 at 15:38

How to generate a combined Q object from a list?

1 Answers1