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DRF Serializers

[!danger] Don't use DRF Serializers to create model instances! [[Scaling Django - Where to put business logic]]

Nested model

Dashboard
    name
    pages

Pages
    name
    widgets

Widgets
    name

Deserializing (usage)

Database to JSON

dashboards = DashboardSerializer(
    Dashboard.objects.all(),
    many=True)
.data

Creating the Serializer

SerializerMethodField

  • return anything you want in the serializer data
  • read-only 
class DashboardSerializer(serializers.ModelSerializer):
    dashboard_pages = serializers.SerializerMethodField("get_dashboard_pages")
    # just want an array of pages?
    # dashboard_pages = PageSerializer(many=True)

    class Meta:
        model = Page
        fields = ("id", "name", "dashboard_pages")

    def get_dashboard_pages(self, dashboard: Dashboard):
        page_query_set = Page.objects.filter(dashboard=dashboard)
        pages = PageSerializer(page_query_set, many=True, read_only=True).data
        return {page["id"]: page for page in pages}

Serializing

JSON to database

Code in view.py

try:
    dashboard = Dashboard.objects.get(id=id)
except Dashboard.DoesNotExist:
    pass

# updates if you pass an instance of the model
# DashboardSerializer(data=data) to create
serialized_dashboard = DashboardSerializer(dashboard, data=data)
if serialized_dashboard.is_valid(raise_exception=True):
    serialized_dashboard.save()  # triggers serializer update() or create()

update()

def update(self, instance: Dashboard, validated_data: dict):
    instance.name = validated_data.get("name", instance.name)
    instance.save()

    for page_data in pages:
        page = Page.objects.get(id=page_data["id"])
        serialized_page = PageSerializer(page, data=page_data)
        if serialized_page.is_valid(raise_exception=True):
            serialized_page.save()

Overriding .save() directly

What is validated_data

When you pass in some data

DashboardSerializer(dashboard, data=data)

Django Rest Framework by default strips all of the properties that are

  • read-only
  • not listed in the fields of the serializer

Update a 1 to 1 foreign key

DashboardWidget <-> DashboardQuery

DashboardWidget.query_file_path

  • string foreign key to DashboardQuery
  • need to set the model
instance.query = DashboardQuery.objects.get(file_path=file_path)

because we can't do .update() because we're given the instance and not a query set

How do I add custom field to the validated_data?

add values to 

DashboardSerializer(data=data).save(name="my_dash")

# dynamic values
key_name = "name"
.save(**{key_name: "my_dash"})

?????

TODO: I don't know what to_internal_value does

implement your own to_internal_value

def to_internal_value(self, data):
    # `data` <=> `self.initial_data`
    if not data.get("query_file_path"):  
        data["query_file_path"] = None  
    return super().to_internal_value(data)

Custom fields

class ColorField(serializers.Field):
    """
    Color objects are serialized into 'rgb(#, #, #)' notation.
    """
    def to_representation(self, value):
        return "rgb(%d, %d, %d)" % (value.red, value.green, value.blue)

    def to_internal_value(self, data):
        data = data.strip('rgb(').rstrip(')')
        red, green, blue = [int(col) for col in data.split(',')]
        return Color(red, green, blue)

https://github.com/beda-software/drf-writable-nested

Custom fields are for serialization or deserialization

If you want a custom nested field that does something like

PageSerializer(many=True)

Except it can return anything you want, ???

Last update: 2023-04-24