Modifying the output from a serializer in the Django Rest Framework

Question

I am using the django rest framework to output the content of an article. It works splendid, except now I want to modify the behavior to not return the full "content", but rather a teaser (of say the first 200 characters of the content but ideally I would like to be able to add any logic, say the end of the first sentence after 200 characters):

class ArticleSerializer(serializers.HyperlinkedModelSerializer):
    user = UserSerializer(many=False, read_only=True)

    class Meta:
        model = models.Article
        fields = (
            'id'
            ,'title'
            , 'date_added'
            , 'content'
            , 'user'
        )

I looked at GenericAPIView where I thought there may be something to override - but nothing looks obvious - can someone lend some insight? Thank you in advance

Answer 1

I'm pretty sure that is what you need:

http://django-rest-framework.org/api-guide/fields.html#serializermethodfield

class ArticleSerializer(serializers.HyperlinkedModelSerializer):
    user = UserSerializer(many=False, read_only=True)
    teaser = serializers.SerializerMethodField('get_teaser')

    class Meta:
        model = models.Article
        fields = (
            'id'
            ,'title'
            , 'date_added'
            , 'user'
            , 'teaser'
        )

    def get_teaser(self, obj):
        return force_text(obj.content[:20])

Answer 2

I am accepting mariodev's solution - as it does work and what I was originally thinking. I did extend my requirements and want to apply the teaser functionality to other fields and thus I ended up with:

from django import forms
from rest_framework.compat import force_text
from rest_framework import serializers, fields

class TeaserField(fields.Field):

    def __init__(self, teaser_length=None, original_field=None):
        self.teaser_length = teaser_length
        self.original_field = original_field
        super(fields.Field, self).__init__()

    def field_to_native(self, obj, field_name):
        if(self.original_field != None):
            field_name = self.original_field

        value = getattr(obj, field_name)
        return self.to_native(value)

    def to_native(self, value):
        def joinEm(chunk):
            teaser = ''
            i=0
            while len(teaser) < self.teaser_length:
                teaser += chunk[i] + '.'
                i += 1

            return teaser

        chunk = value.split('.')
        teaser = joinEm(chunk)

        strongOpenTag = '<strong>'
        strongOpen = teaser.find(strongOpenTag)
        strongClose = teaser.find('</strong>')

        if(strongOpen > 0 and strongClose < 0):
            teaser  = teaser.replace(strongOpenTag,'')

        return force_text(teaser)

---

Previous solution

This is my current working solution, would love to know opinions on this.

from django import forms
from rest_framework.compat import force_text

class TeaserField(fields.CharField):
    def __init__(self, teaser_length=None, *args, **kwargs):
        self.teaser_length = teaser_length
        super(TeaserField, self).__init__(*args, **kwargs)

    def to_native(self, value):
        return force_text(value[:self.teaser_length])


class ArticleSerializer(serializers.HyperlinkedModelSerializer):
    user = UserSerializer(many=False, read_only=True)
    content = TeaserField(teaser_length=20)
    class Meta:
        model = models.Article
        fields = (
            'id'
            ,'title'
            , 'date_added'
            , 'content'
            , 'user'
        )


class IdeaSerializer(serializers.HyperlinkedModelSerializer):
    user = UserSerializer(many=False, read_only=True)
    teaser = myFields.TeaserField(teaser_length=200, original_field='content')

    class Meta:
        model = myModels.Idea
        fields = (
            'id'
            ,'title'
            , 'date_added'
            , 'user'
            , 'content'
            , 'teaser'
        )