Converting a QuerySet to dictionary without iterating in Python?

Question

I would like to store certain fields from a QuerySet object into a python object (e.g. dictionary), but I wonder if it is possible to do this without looping, at least explicitly, in Python?

For example, if the content of the QuerySet are as follows:

>> queryset.values_list('parents', 'children', 'x', 'y')
>> [('parent1', 'child1', 1.1, 1.03), ('parent1', 'child2', 1.4, 1.05), ('parent2', 'child1', 0.1, 0.2), ('parent2', 'child2', 1.3, 2.2)]

Now, I would like to convert this into a dictionary. The actual structure of the dictionary is of secondary importance, as long as all the information is contained. E.g.:

d = {
  'child1': {
    'parent1' : [1.1, 1.03], 
    'parent2' : [0.1, 0.2], 
  ...
}

# or
d = {
  'parent1': {
    'child1': [1.1, 1.03], 
    'child2': [1.4, 1.05]
  ...
}

# or even: 
d = {
  'child1': [
    # parent1   # parent2
    (1.1, 1.03), (0.1, 0.2)
  ]
  ...
}

Of course, I can do this if I loop through the queryset in Python, but is it really necessary to do an explicit for loop? Is there a way to populate the dictionary directly from the queryset, similar to how list(queryset) gives you a list?

I mostly worry that a for loop will not scale well in terms of performance if I need to retrieve tens of thousands of similar entries. I know that possibly iteration is unavoidable, but at least I'd like to avoid doing that explicitly.

Everything I found online shows how to do this by iterating over the queryset in Python, which is clear to me, but I wonder if there are other, perhaps more performant, ways of doing this.

What about values method? docs.djangoproject.com/en/4.1/ref/models/querysets/… — vinkomlacic
– vinkomlacic, Commented Oct 3, 2022 at 18:54
I have considered it, but that still returns a queryset object. I need the output to be a python dictionary :/ — besi
– besi, Commented Oct 3, 2022 at 18:59

Mahmoud Nasser · Accepted Answer · 2022-10-03 18:56:08Z

1

Use Serializers:

from rest_framework import serializers
class SomeModelSerializer(serializers.ModelSerializer):
    class Meta:
        model = SomeModel
        fields = "__all__"

SomeModelSerializer(instance).data

returns

{'auto_now_add': '2018-12-20T21:34:29.494827Z',
 'foreign_key': 2,
 'id': 1,
 'many_to_many': [2],
 'normal_value': 1,
 'readonly_value': 2}

I think this solution has good performance.I trust Django REST Framework team :)

answered Oct 3, 2022 at 18:56

Mahmoud Nasser

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7 Comments

besi Over a year ago

This is really interesting and something I have not considered at all. Will definitely give it a try. Thanks for the suggestion!

Mahmoud Nasser Over a year ago

Your Welcome My Friend please do upvote to encourage me helping more people :)

besi Over a year ago

If I understand correctly, this works on a model instance, not queryset, correct? So this is just like doing vars(instance)? Maybe I am not using it correctly, but I don't see how this does what I am going for?

Mahmoud Nasser Over a year ago

You could pass to it a querset the set the many attribute to true

besi Over a year ago

This is really cool! I think this is quite close to what I am trying to do. One thing about my case is that I also want to get related fields (e.g. parent__value). Is it possible to include those fields with the above ModelSerializer? Currently, it gives me an ImproperlyConfigured error saying the field name is not valid for my model.

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