Django Rest Framework - Interrelated serializers

Question

Given the following models for which two have a ManyToMany relationship with the first, how can I construct a serializer for all three models?

This is where the importance of ordering in Python is turning to be an issue.

class Trail(models.Model):
    '''
    Main model for this application.  Contains all information for a particular trail
    '''
    trail_name = models.CharField(max_length=150)
    active = models.BooleanField(default=True)
    date_uploaded = models.DateTimeField(default=now())
    owner = models.ForeignKey(Account, default=1)


    class Meta:
        ordering = ('trail_name', )

class Activity(models.Model):
    '''
    A many to many join table to map an activity name to a trail.  A trail can have many
    activities
    '''
    name = models.CharField(max_length=40, unique=True)
    trails = models.ManyToManyField(Trail)

    class Meta:
        ordering = ('name', )


class Surface(models.Model):
    '''
    A many to many join table to map a surface type to many trails.  A trail can have many
    surface types.
    '''
    type = models.CharField(max_length=50, db_column='surface_type', unique=True)
    trails = models.ManyToManyField(Trail)

    class Meta:
        ordering = ('type', )

I have the following serializers in serializers.py :

class TrailSerializer(serializers.ModelSerializer):
    owner = AccountSerializer()
    activities = ActivitySerializer()

    class Meta:
        model = Trail
        fields = ('trail_name', 'active', 'date_uploaded', 'owner', 'activities', )


class ActivitySerializer(serializers.ModelSerializer):
    trails = TrailSerializer()

    class Meta:
        model = Activity
        fields = ('trails', 'name', )


class SurfaceSerializer(serializers.ModelSerializer):
    trails = TrailSerializer()

    class Meta:
        model = Surface
        fields = ('trails', 'type', )

My question is, short of creating another file to contain ActivitySerializer and SurfaceSerializer , how can I ensure that TrailSerializer works as expected in order to include Activity and Surface references during serialization?

Answer 1

Use Marshmallow (serialization library inspired in part by DRF serializers). It solves this problem, by allowing nested schemas to be reference as strings. See Marshmallow: Two Way Nesting

class AuthorSchema(Schema):
    # Make sure to use the 'only' or 'exclude' params to avoid infinite recursion
    books = fields.Nested('BookSchema', many=True, exclude=('author', ))
    class Meta:
        fields = ('id', 'name', 'books')

class BookSchema(Schema):
    author = fields.Nested(AuthorSchema, only=('id', 'name'))
    class Meta:
        fields = ('id', 'title', 'author')

You can use directly or use via django-rest-marshmellow by Tom Christie , which allows use of Marshmallow, while maintaining the same API as REST framework's Serializer class.

I'm not aware of a way to achieve the same result using just DRFs serializers.

See also: Why Marshmallow?