Retrieving a Foreign Key value with django-rest-fr

Question

I'm using the django rest framework to create an API. I have the following models:

class Category(models.Model):
    name = models.CharField(max_length=100)

    def __unicode__(self):
        return self.name


class Item(models.Model):
    name = models.CharField(max_length=100)
    category = models.ForeignKey(Category, related_name='items')

    def __unicode__(self):
        return self.name

To create a serializer for the categories I'd do:

class CategorySerializer(serializers.ModelSerializer):
    items = serializers.RelatedField(many=True)

    class Meta:
        model = Category

... and this would provide me with:

[{'items': [u'Item 1', u'Item 2', u'Item 3'], u'id': 1, 'name': u'Cat 1'},
 {'items': [u'Item 4', u'Item 5', u'Item 6'], u'id': 2, 'name': u'Cat 2'},
 {'items': [u'Item 7', u'Item 8', u'Item 9'], u'id': 3, 'name': u'Cat 3'}]

How would I go about getting the reverse from an Item serializer, ie:

[{u'id': 1, 'name': 'Item 1', 'category_name': u'Cat 1'},
{u'id': 2, 'name': 'Item 2', 'category_name': u'Cat 1'},
{u'id': 3, 'name': 'Item 3', 'category_name': u'Cat 1'},
{u'id': 4, 'name': 'Item 4', 'category_name': u'Cat 2'},
{u'id': 5, 'name': 'Item 5', 'category_name': u'Cat 2'},
{u'id': 6, 'name': 'Item 6', 'category_name': u'Cat 2'},
{u'id': 7, 'name': 'Item 7', 'category_name': u'Cat 3'},
{u'id': 8, 'name': 'Item 8', 'category_name': u'Cat 3'},
{u'id': 9, 'name': 'Item 9', 'category_name': u'Cat 3'}]

I've read through the docs on reverse relationships for the rest framework but that appears to be the same result as the non-reverse fields. Am I missing something obvious?

Answer 1

Another thing you can do is to:

• create a property in your Item model that returns the category name and
• expose it as a ReadOnlyField.

Your model would look like this.

class Item(models.Model):
    name = models.CharField(max_length=100)
    category = models.ForeignKey(Category, related_name='items')

    def __unicode__(self):
        return self.name

    @property
    def category_name(self):
        return self.category.name

Your serializer would look like this. Note that the serializer will automatically get the value of the category_name model property by naming the field with the same name.

class ItemSerializer(serializers.ModelSerializer):
    category_name = serializers.ReadOnlyField()

    class Meta:
        model = Item

Answer 2

Worked on 08/08/2018 and on DRF version 3.8.2:

class ItemSerializer(serializers.ModelSerializer):
    category_name = serializers.ReadOnlyField(source='category.name')

    class Meta:
        model = Item
        read_only_fields = ('id', 'category_name')
        fields = ('id', 'category_name', 'name',)

Using the Meta read_only_fields we can declare exactly which fields should be read_only. Then we need to declare the "foreign" field on the Meta fields (better be explicit as the mantra goes: zen of python).

Answer 3

Just use a related field without setting many=True.

Note that also because you want the output named category_name, but the actual field is category, you need to use the source argument on the serializer field.

The following should give you the output you need...

class ItemSerializer(serializers.ModelSerializer):
    category_name = serializers.RelatedField(source='category', read_only=True)

    class Meta:
        model = Item
        fields = ('id', 'name', 'category_name')

Answer 4

Simple solution source='category.name' where category is foreign key and .name it's attribute.

from rest_framework.serializers import ModelSerializer, ReadOnlyField
from my_app.models import Item

class ItemSerializer(ModelSerializer):
    category_name = ReadOnlyField(source='category.name')

    class Meta:
        model = Item
        fields = __all__

Answer 5

this worked fine for me:

class ItemSerializer(serializers.ModelSerializer):
    category_name = serializers.ReadOnlyField(source='category.name')
    class Meta:
        model = Item
        fields = "__all__"

Answer 6

In the current DRF(3.6.3) version this worked for me

class ItemSerializer(serializers.ModelSerializer):
    category_name = serializers.CharField(source='category.name')

    class Meta:
        model = Item
        fields = ('id', 'name', 'category_name')