Django REST Framework adding additional field to ModelSerializer

Question

I want to serialize a model  but want to include an additional field that requires doing some database lookups on the model instance to be serialized   class FooSerializer serializers ModelSerializer     my field         result of some database queries on the input Foo object   class Meta          model   Foo         fields     id    name    myfield     What is the right way to do this  I see that you can pass in extra  context  to the serializer  is the right answer to pass in the additional field in a context dictionary  With that approach  the logic of getting the field I need would not be self-contained with the serializer definition  which is ideal since every serialized instance will need my field  Elsewhere in the DRF serializers documentation it says  extra fields can correspond to any property or callable on the model   Is extra fields what I m talking about  Should I define a function in Foo s model definition that returns my field value  and in the serializer I hook up my field to that callable  What does that look like   Thanks in advance  happy to clarify the question if necessary

User · Accepted Answer

I think SerializerMethodField is what you're looking for:

class FooSerializer(serializers.ModelSerializer):
  my_field = serializers.SerializerMethodField('is_named_bar')

  def is_named_bar(self, foo):
      return foo.name == "bar" 

  class Meta:
    model = Foo
    fields = ('id', 'name', 'my_field')

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

User · Answer

if you want read and write on your extra field  you can use a new custom serializer  that extends serializers Serializer  and use it like this  class ExtraFieldSerializer serializers Serializer       def to representation self  instance              this would have the same as body as in a SerializerMethodField         return  my logic here       def to internal value self  data             This must return a dictionary that will be used to           update the caller s validation data  i e  if the result           produced should just be set back into the field that this           serializer is set to  return the following          return             self field name   Any python object made with data   s    data            class MyModelSerializer serializers ModelSerializer       my extra field   ExtraFieldSerializer source           class Meta          model   MyModel         fields     id    my extra field     i use this in related nested fields with some custom logic

User · Answer

class Demo models Model                property     def property name self                If you want to use the same property name  class DemoSerializer serializers ModelSerializer       property name   serializers ReadOnlyField       class Meta          model   Product         fields      all      or you can choose your own fields  If you want to use different property name  just change this  new property name   serializers ReadOnlyField source  property name

User · Answer

With the last version of Django Rest Framework  you need to create a method in your model with the name of the field you want to add  No need for  property and source  field  raise an error   class Foo models Model                 def foo self           return  stuff             class FooSerializer ModelSerializer       foo   serializers ReadOnlyField        class Meta          model   Foo         fields     foo

User · Answer

You can change your model method to property and use it in serializer with this approach   class Foo models Model                  property     def my field self           return stuff            class FooSerializer ModelSerializer       my field   serializers ReadOnlyField source  my field        class Meta          model   Foo         fields     my field      Edit  With recent versions of rest framework  I tried 3 3 3   you don t need to change to property  Model method will just work fine

User · Answer

My response to a similar question  here  might be useful   If you have a Model Method defined in the following way   class MyModel models Model                def model method self           return  some calculated result    You can add the result of calling said method to your serializer like so   class MyModelSerializer serializers ModelSerializer       model method field   serializers CharField source  model method     p s  Since the custom field isn t really a field in your model  you ll usually want to make it read-only  like so   class Meta      model   MyModel     read only fields              model method field

User · Answer

This worked for me  If we want to just add an additional field in ModelSerializer  we can do it like below  and also the field can be assigned some val after some calculations of lookup  Or in some cases  if we want to send the parameters in API response  In model py class Foo models Model        quot  quot  quot Model Foo quot  quot  quot      name   models CharField max length 30  help text  quot Customer Name quot    In serializer py class FooSerializer serializers ModelSerializer       retrieved time   serializers SerializerMethodField             classmethod     def get retrieved time self  object            quot  quot  quot getter method to add field retrieved time quot  quot  quot          return None    class Meta          model   Foo         fields     id    name    retrieved time     Hope this could help someone

User · Answer

As Chemical Programer said in this comment  in latest DRF you can just do it like this   class FooSerializer serializers ModelSerializer       extra field   serializers SerializerMethodField        def get extra field self  foo instance           return foo instance a   foo instance b      class Meta          model   Foo         fields     extra field          DRF docs source

[django] Django REST Framework: adding additional field to ModelSerializer

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