CODEWITHSUNDEEP
djangodjango-models
Skander
Skander

Reputation: 230

Django: Add arbitrary additional data to a queryset

I am trying to display a map of my data based on a search. The easiest way to handle the map display would be to serialized the queryset generated by the search, and indeed this works just fine using . However, I'd really like to allow for multiple searches, with the displayed points being shown in a user chosen color. The user chosen color, obviously cannot come from the database, since it is not a property of these objects, so none of the aggregators make sense here.

I have tried simply making a utility class, since what I really need is a somewhat complex join between two model classes that then gets serialized into geojson. However, once I created that utility class, it became evident that I lost a lot of the benefits of having a queryset, especially the ability to easily serialize the data with django-geojson (or natively once I can get 1.8 to run smoothly).

Basically, I want to be able to do something like:

querySet = datumClass.objects.filter(...user submitted search parameters...).annotate(color='blue')

Is this possible at all? It seems like this would be more elegant and would work better than my current solution of a non-model utility class which has some serious serialization issues when I try to use python-geojson to serialize.

Upvotes: 4

Views: 4491

Answers (3)

wobbily_col
wobbily_col

Reputation: 11879

Not quite sure what you are trying to achieve, but you can add extra attributes to your objects iterating over the queryset in the view. These can be accessed from the template.

for object in queryset :
    if object.contition = 'a'
        object.color = 'blue'
    else:
        object.color = 'green'

Upvotes: 2

codeblur
codeblur

Reputation: 438

The problem is that extra comes with all sorts of warning about usefulness or deprecation... But this works:

.extra(select={'color': "'blue'"})

Notice the double quotes wrapping the string value.

This translates to:

SELECT ('blue') AS "color"

Upvotes: 2

C.B.
C.B.

Reputation: 8326

if you have a dictionary that maps fields to values, you can do things like

filter_dictionary = {
    'date__lte' : '2014-03-01'
}
qs = DatumClass.objects.filter(**filter_dictionary)

And qs would have all dates less than that date (if it has a date field). So, as a user, I could submit any key, value pairs that you could place in your dictionary.

Upvotes: 0

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