Django: Add a list to a QuerySet

Question

I am new to django so apologies if this is not possible or easy.

I have a view that takes a subset of a model

data = Terms.objects.filter(language = language_id)

The subset is one language. The set has a number of concepts for a language. Some languages might use the same word for multiple concepts, and I want to colour these the same in an SVG image. So I do this next:

for d in data:
    if d.term is None:
        d.colour = "#D3D3D3"
    else:
        d.colour = termColours[d.term]

Where termColours is a dictionary with keys as the unique terms and values as the hexadecimal colour I want.

I thought this would add a new colour attribute to my queryset. However, when I convert the queryset to json (in order to pass it to JS) the colour object is not there.

    terms_json = serializers.serialize('json', data)

How can I add a new colour element to my queryset?

.values() will turn your queryset into a list of dictionaries. As such, they can be modified as you please. — Paolo Stefan, May 02 '18 at 13:34

score 1 · Accepted Answer · answered May 02 '18 at 13:29

1

Convert your Queryset to Dict and then modify values.

Ex:

data = Terms.objects.filter(language = language_id).values()
for d in data:
    if d.term is None:
        d.colour = "#D3D3D3"
    else:
        d.colour = termColours[d.term]

answered May 02 '18 at 13:29

Rakesh

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This breaks the serialisation line with "AttributeError: 'dict' object has no attribute '_meta'" – SamPassmore May 02 '18 at 13:35
This should help. https://stackoverflow.com/questions/46062242/queryset-serialize-attributeerror-dict-object-has-no-attribute-meta – Rakesh May 02 '18 at 13:37

score 0 · Answer 2 · answered May 02 '18 at 15:10

If I understand correctly - you need Django ORM annotation. And it might look like that:

from django.db.models import Case, When, Value

data = Terms.objects.filter(language = language_id)
                     .annotate(color = Case(
                               When(term__isnull = True, then = "#D3D3D3"),
                               When(term__isnull = False, then = termColours[Value(term)]),))

Only problem here - I don't exactly know this moment - termColours[Value(term)], you need to test different combinations of that expressions to get the value of field term.

Django: Add a list to a QuerySet

2 Answers2