Enumerating model choices in a Django Rest Framework serializer

Question

I have a model that uses a Django choices field, like this:

class Question(models.Model):
QUESTION_TYPES = (
    (10,'Blurb'),
    (20,'Group Header'),
    (21,'Group Footer'),
    (30,'Sub-Group Header'),
    (31,'Sub-Group Footer'),
    (50,'Save Button'),
    (100,'Standard Question'),
    (105,'Text-Area Question'),
    (110,'Multiple-Choice Question'),
    (120,'Standard Sub-Question'),
    (130,'Multiple-Choice Sub-Question')
)
type = models.IntegerField(default=100,choices=QUESTION_TYPES)

I'm using Django Rest Framework to present this model as an API to an Angular web app. In my Angular web app, I want a combo box widget that drops down with all those choices. Not the integers, but the text choices, like "blurb", "standard question" and so on.

Now, I could hand code the combo box into the Angular app, but in the spirit of DRY, is it possible to write a DRF serializer that just returns those choices (ie the QUESTION_TYPES object), so I can populate the combo box with a ReST query?

And by "possible", I guess I mean "simple and elegant". And maybe I also mean "ReSTful". (Is it ReSTful to do it that way?)

Just wondering . . .

Thanks

John

Answer 1

I would probably try something like the following:

# models.py
class Question(models.Model):
    QUESTION_NAMES = (
        'Blurb',
        'Group Header',
        'Group Footer',
        'Sub-Group Header',
        'Sub-Group Footer',
        'Save Button',
        'Standard Question',
        'Text-Area Question',
        'Multiple-Choice Question',
        'Standard Sub-Question',
        'Multiple-Choice Sub-Question')
    QUESTION_VALS = (10, 20, 21, 30,
                     31, 50, 100, 105, 110,
                     120, 130)
    QUESTION_TYPES = tuple(zip(QUESTION_VALS, QUESTION_NAMES))
    # Personal choice here: I never name attribs after Python built-ins:
    qtype = models.IntegerField(default=100,choices=QUESTION_TYPES)

---

The following doesn't work as I thought it should

(Following was my original intuition on serializing a list of objects, but it did not work. I'm leaving it in here anyway, because it seems like it should work.)

Okay, so we have a way to access the strings on their own, now we just need to serialize them, and for that, I'd probably try to use the ListField in DRF3, which should support the source kwarg, I would think?

# serializers.py
from .models import Question
class YourSerializer(ModelSerializer):
    names = serializers.ListField(
       child=serializers.CharField(max_length=40),
       source=Question.QUESTION_NAMES
    )
    class Meta:
        model = Question
        fields = ('names', etc.)

---

The following does return a list of results

Fallback: use a SerializerMethodField:

from .models import Question

class YourSerializer(serializers.ModelSerializer):
    ...
    names = serializers.SerializerMethodField()

    def get_names(self, obj):
        return Question.QUESTION_NAMES

    class Meta:
        model = Question

Demo:

In [1]: q = Question.objects.create()
Out[1]: <Question: Question object>  

In [2]: ser = YourSerializer(q)

In [3]: ser.data
Out[3]: {'id': 1, 'names': ['Blurb', 'Group Header', 'Group Footer', 'Sub-Group Header', 'Sub-Group Footer', 'Save Button', 'Standard Question', 'Text-Area Question', 'Multiple-Choice Question', 'Standard Sub-Question', 'Multiple-Choice Sub-Question'], 'qtype': 100}

Answer 2

if you use a ModelViewSet in combination with a ModelSerializer, the OPTIONS request will return metadata that you can use to get the choice options.

from models import Question
from rest_framework import serializers

class QuestionSerializer(serializers.ModelSerializer):
    class Meta:
        model = Question


from rest_framework.viewsets import ModelViewSet
class QuestionChoicesViewSet(ModelViewSet):
    queryset = Question.objects.all()
    serializer_class = QuestionSerializer

This will give you a response that includes the actions attribute, that might look something like this:

"actions": {
    "POST": {
        "id": {
            "type": "integer",
            "required": false,
            "read_only": true,
            "label": "ID"
        },
        "qtype": {
            "type": "choice",
            "required": false,
            "read_only": false,
            "label": "Qtype",
            "choices": [
                {
                    "display_name": "Blurb",
                    "value": 10
                },
                {
                    "display_name": "Group Header",
                    "value": 20
                },
                {
                    "display_name": "Group Footer",
                    "value": 21
                },
                {
                    "display_name": "Sub-Group Header",
                    "value": 30
                },
                //...
        }
    }
}

You can iterate over the choices attribute on qtype to get all of the available choices.

To get more familiar with this topic you can read: Metadata