Serialization of parent model including child models

Question

I have models - Commodity, Clother and child models, as Acessories, Outwear, etc.:

class Commodity(models.Model):
    atribute = models.CharField()

class Clother(models.Model):
    commodity = models.ForeignKey(Commodity)
    clother_atribute = models.CharField()

class Acessories(models.Model):
    clother = models.ForeignKey(Clother)
    acessories_atribute = models.CharField() 

class Outwear(models.Model):
    clother = models.ForeignKey(Clother)
    outwear_atribute = models.CharField()

How can I serialize the parent model Commodity to call all vertical dependencies? I suppose to query Commodity id and get all Clother attributes and Acessories or Outwear attributes.

Well since there is no concept in Django like "vertical dependencies", you probably have to list those yourself. Yes, you can walk through the model-relation graph, but detecting cycles make things complicated. — Willem Van Onsem, Jun 21 '18 at 12:57

score 12 · Accepted Answer · answered Jun 21 '18 at 12:59

12

If I understood your problem you can define ClotherSerializer. You can use depth = 1 to serialize nested objects in this serializer:

class ClotherSerializer(serializers.ModelSerializer):
    class Meta:
        model = Clother
        fields = ('id', 'acessories_set', 'outwear_set')
        depth = 1

Later in your CommoditySerializer you can use ClotherSerializer to serialize clother and all it's relation:

class CommoditySerializer(serializers.ModelSerializer):
    clother_set = ClotherSerializer(many=True)
    class Meta:
        model = Commodity
        fields = ('id', 'clother_set')

answered Jun 21 '18 at 12:59

neverwalkaloner

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Can you actually passe a list of children in the parent's object, to create a parent and multiple children at the same time? Have tried but for some reason it seems that the parent object doesn't accept a list of children objects, although their relationship has been clearly defined in their models. Any hint on how to manage this? – Seb Oct 06 '20 at 10:09
@Seb try to check writable nested serializer part in the docs: https://www.django-rest-framework.org/api-guide/relations/#writable-nested-serializers – neverwalkaloner Oct 06 '20 at 12:02
Thanks for the reply. So have tried but am still getting an error "Invalid data. Expected a dictionary, but got list." in the parent's object field corresponding to its children. Any hint on why it behaves that way when I have a many to one relationship between the children and the parent? – Seb Oct 08 '20 at 02:04
1

You my friend saved me so much time. For whatever reason I could not figure out this simple `depth = 1` fix. Thank you!! :) – Emmet Arries Aug 17 '22 at 00:05

mrehan · Answer 2 · 2018-06-22T16:15:32.483

Alternatively, this can also be achieved using SerializerMethodField: http://www.django-rest-framework.org/api-guide/fields/#serializermethodfield

class ClotherSerializer(serializers.ModelSerializer):
    """
    Serializer for Clother data model.
    """
    acessories = serializers.SerializerMethodField()
    outwears = serializers.SerializerMethodField()

    class Meta:
        model = Clother
        fields = ('id', 'acessories', 'outwears')

    def get_acessories(self, clother):
        return AcessoriesSerializer(clother.acessories_set.all(), many=True).data

    def get_outwears(self, clother):
        return OutwearSerializer(clother.outwear_set.all(), many=True).data


class CommoditySerializer(serializers.ModelSerializer):
    """
    Serializer for Commodity data model.
    """
    clother = serializers.SerializerMethodField()

    class Meta:
        model = Commodity
        fields = ('id', 'clother')

    def get_clother(self, commodity):
        return ClotherSerializer(commodity.clother_set.all(), many=True).data

score 2 · Answer 3 · answered Jun 21 '18 at 13:03

You can use the drf-writable-nested [GitHub] package for that and specify in a serializer how to serialize certain fields. By using another serializer, you thus specify that it it serialized by calling the serializer for these children:

class CommoditySerializer(WritableNestedModelSerializer):
    clother_set = ClotherSerializer(many=True)

    class Meta:
        model = Commodity
        fields = ("atribute", 'clother_set')


class ClotherSerializer(WritableNestedModelSerializer):

    class Meta:
        model = Clother
        fields = ("clother_atribute",)

Of course you can add more such relations, for example to specify Acessories for a Clother.

I advice you look at the GitHub page, and use this as a template for your own serializer.

score 0 · Answer 4 · answered Jul 21 '22 at 09:28

To achieve this functionality natively without any extra methods, you need only get the Clother dependency to the Commodity using it's related name. In this case, since the related_name reference is not defined, use the default related name like so:

...
class ClotherSerializer(serializers.ModelSerializer):
    """
    Serializer for Clother data model.
    """
    acessories_set = AccesoriesSerializer(many=True, read_only=True)
    outwears_set = OutwearsSerializer(many=True,read_only=True)

    class Meta:
        model = Clother
        fields = ('id', 'acessories_set', 'outwears_set')


class CommoditySerializer(serializers.ModelSerializer):
    """
    Serializer for Commodity data model.
    """
    clother_set = ClotherSerializer(many=True, read_only=True)

    class Meta:
        model = Commodity
        fields = ('id', 'clother_set')

Serialization of parent model including child models

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