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How to deal with nested serializer fields in Django Rest Framework?

I have nested serializer (AmountSerializer). I need a field meal_name in one ViewSet. But when this field is nested, I don't need it to be seen in endpoint(in MealSerializer). How to exclude field from nested serializer when is it actually nested?
models.py:
class MealType(models.Model):
name = models.TextField()
def __str__(self):
return self.name
class Ingredient(models.Model):
name = models.TextField()
def __str__(self):
return self.name
class Meal(models.Model):
name = models.TextField()
type = models.ForeignKey(MealType, on_delete=models.CASCADE, default=None)
recipe = models.TextField()
photo = models.ImageField(null=True, height_field=None, width_field=None, max_length=None,upload_to='media/')
ingredients = models.ManyToManyField(Ingredient)
def __str__(self):
return self.name
class IngredientAmount(models.Model):
ingredient_name = models.ForeignKey(Ingredient, on_delete=models.CASCADE, default=None)
amount = models.FloatField(default=None)
meal = models.ForeignKey(Meal, on_delete=models.CASCADE, default=None, related_name='meal_id')
class Meta:
ordering = ['meal']
def __str__(self):
return self.ingredient_name
serializers.py:
class AmountSerializer(serializers.ModelSerializer):
ingredient_name= serializers.ReadOnlyField(source='ingredient_name.name')
-->#meal_name = serializers.ReadOnlyField(source='meal.name')
#I CAN'T use ReadOnlyField( #with write_only=True)
#i trired use PrimaryKeyRelatedField
# butgot AssertionError: Relational field must provide a `queryset` argument, override `get_queryset`, or set read_only=`True`.
class Meta:
model = IngredientAmount
fields = ('ingredient_name','amount','meal_name')
class MealSerializer(serializers.ModelSerializer):
type_name= serializers.ReadOnlyField(source='type.name')
ingredients = serializers.SlugRelatedField(read_only=True, slug_field='name', many=True)
amount = AmountSerializer(read_only=True, many=True,source='meal_id')
class Meta:
model = Meal
fields = ('id', 'name', 'type_name', 'recipe', 'photo', 'ingredients','amount')

I'd rather use a trick to exclude some of the fields that are not needed in certain situations. You can inherit your serializer from ExcludeFieldsModelSerializer, and exclude any fields that you want so that the serializer will not serialize that field.
class ExcludeFieldsModelSerializer(serializers.ModelSerializer):
"""
A ModelSerializer that takes an additional `exclude_fields` argument that
controls which fields should be excluded from the serializer.
Plagiarised from https://www.django-rest-framework.org/api-guide/serializers/#dynamically-modifying-fields
"""
def __init__(self, *args, **kwargs):
# Don't pass the 'exclude_fields' arg up to the superclass
exclude_fields = kwargs.pop('exclude_fields', None)
# Instantiate the superclass normally
super(ExcludeFieldsModelSerializer, self).__init__(*args, **kwargs)
if exclude_fields is not None:
# Drop any fields that are specified in the `exclude_fields` argument.
drop = set(exclude_fields)
for field_name in drop:
self.fields.pop(field_name)
class AmountSerializer(ExcludeFieldsModelSerializer):
ingredient_name= serializers.ReadOnlyField(source='ingredient_name.name')
meal_name = serializers.CharField(read_only=True, source='meal.name')
class Meta:
model = IngredientAmount
fields = ('ingredient_name','amount','meal_name')
class MealSerializer(serializers.ModelSerializer):
type_name= serializers.ReadOnlyField(source='type.name')
ingredients = serializers.SlugRelatedField(read_only=True, slug_field='name', many=True)
amount = AmountSerializer(read_only=True, many=True, source='meal_id', exclude_fields={'meal_name'})
class Meta:
model = Meal
fields = ('id', 'name', 'type_name', 'recipe', 'photo', 'ingredients','amount')

Showing extra field on ManyToMany relationship in Django serializer

I have a ManyToMany field in Django, like this:
class Dictionary(models.Model):
traditional = models.CharField(max_length=50)
simplified = models.CharField(max_length=50)
pinyin_numbers = models.CharField(max_length=50)
pinyin_marks = models.CharField(max_length=50)
translation = models.TextField()
level = models.IntegerField()
frequency = models.IntegerField()
idiom = models.BooleanField()
child_char = models.ManyToManyField('Dictionary', through='DictionaryChildChar', null=True)
class Meta:
db_table = 'dictionary'
indexes = [
models.Index(fields=['simplified', ]),
models.Index(fields=['traditional', ]),
]
class DictionaryChildChar(models.Model):
class Meta:
db_table = 'dictionary_child_char'
from_dictionary = models.ForeignKey(Dictionary, on_delete=models.CASCADE, related_name="from_dictionary")
to_dictionary = models.ForeignKey(Dictionary, on_delete=models.CASCADE, related_name="to_dictionary")
word_order = models.IntegerField()
Currently, I have a serializer like this:
class FuzzySerializer(serializers.ModelSerializer):
pinyin = serializers.CharField(
required=False, source="pinyin_marks")
definition = serializers.CharField(
required=False, source="translation")
hsk = serializers.CharField(required=False, source="level")
class Meta:
model = Dictionary
fields = ["id", "simplified", "pinyin", "pinyin_numbers","definition", "hsk", "traditional", "child_char"]
depth = 1
This gives me a dictionary entry, as well as the child dictionary entries associated with it (as a Chinese word is made up of several Chinese characters)
However, I need to know what order these child characters are in, and hence why I have word_order.
I would like this word_order field to appear on the individual child_char - how do I write my serializer in such a way that this additional field is present? Would I need to make a separate serializer for child_char?
EDIT: I have tried this serializer, it doesn't work:
class FuzzyChildCharSerializer(serializers.ModelSerializer):
class Meta:
model = DictionaryChildChar
fields = ["word_order"]

Easiest way is to create a dedicated FuzzyChildCharSerializer and then connect it to your original serializer as a nested relationship:
class FuzzyChildCharSerializer():
class Meta:
model = DictionaryChildChar
fields = ["word_order"] # And whatever other fields you want
class FuzzySerializer():
child_char = FuzzyChildCharSerializer(many=True)
...
You could also write a SerializerMethodField.

It appears I had to bridge the connection via the glue table, which makes sense.
class FuzzyChildCharSerializer(serializers.ModelSerializer):
pinyin = serializers.CharField(
required=False, source="pinyin_marks")
definition = serializers.CharField(
required=False, source="translation")
hsk = serializers.CharField(required=False, source="level")
class Meta:
model = Dictionary
fields = ["id", "simplified", "pinyin", "pinyin_numbers","definition", "hsk", "traditional",]
class FuzzyChildCharSerializerGlue(serializers.ModelSerializer):
to_dictionary = FuzzyChildCharSerializer()
class Meta:
model = DictionaryChildChar
fields = '__all__'
class FuzzySerializer(serializers.ModelSerializer):
pinyin = serializers.CharField(
required=False, source="pinyin_marks")
definition = serializers.CharField(
required=False, source="translation")
hsk = serializers.CharField(required=False, source="level")
from_dictionary = FuzzyChildCharSerializerGlue(many=True)
class Meta:
model = Dictionary
fields = ["id", "simplified", "pinyin", "pinyin_numbers","definition", "hsk", "traditional", "from_dictionary"]
depth = 1
This provides each character with its given word order

Order post by date

I've created a list of post and now I want order this list by date of publishing. If I use order_by(-post_publishing_date) in the view the shell show me this error:
NameError: name 'post_publishing_date' is not defined
models.py
class PostModel(models.Model):
post_title = models.CharField(max_length=70)
post_short_description = models.TextField(max_length=200)
post_contents = models.TextField()
post_publishing_date = models.DateTimeField(auto_now=False, auto_now_add=True)
post_author = models.ForeignKey(AuthorModel, on_delete=models.CASCADE, related_name="connected_author")
post_keyconcept = models.ManyToManyField(KeyConceptModel, related_name="connected_keyconcept")
slug = models.SlugField(verbose_name="Slug", unique="True")
post_highlighted = models.BooleanField(default=False)
def __str__(self):
return self.post_title
def get_absolute_url(self):
return reverse("singlepostManuscriptusView", kwargs={"slug": self.slug})
class Meta:
verbose_name = "Articolo"
verbose_name_plural = "Articoli"
views.py
class SinglePostGDV(DetailView):
model = PostModel
template_name = "manuscriptus_post_detail.html"
class ListPostGDV(ListView):
model = PostModel
template_name = "manuscriptus_home.html"
queryset = PostModel.objects.filter().order_by(-post_publishing_date)
urls.py
urlpatterns = [
path("it/blog/", ListPostGDV.as_view(), name="homeManuscriptusView"),
path("it/blog/<slug:slug>/", SinglePostGDV.as_view(), name="singlepostManuscriptusView"),
]
What I did wrong?

Ad hoc ordering
Well Python is correct. There is no identifier post_publishing_date, you pass the name of the column through a string, so:
class ListPostGDV(ListView):
model = PostModel
template_name = "manuscriptus_home.html"
queryset = PostModel.objects.filter().order_by('-post_publishing_date')
Define an inherent ordering on the model
Note that you can also give a model an "inherent" ordering in the Meta class:
class PostModel(models.Model):
post_title = models.CharField(max_length=70)
post_short_description = models.TextField(max_length=200)
post_contents = models.TextField()
post_publishing_date = models.DateTimeField(auto_now=False, auto_now_add=True)
post_author = models.ForeignKey(AuthorModel, on_delete=models.CASCADE, related_name="connected_author")
post_keyconcept = models.ManyToManyField(KeyConceptModel, related_name="connected_keyconcept")
slug = models.SlugField(verbose_name="Slug", unique="True")
post_highlighted = models.BooleanField(default=False)
def __str__(self):
return self.post_title
def get_absolute_url(self):
return reverse("singlepostManuscriptusView", kwargs={"slug": self.slug})
class Meta:
ordering = ['-post_publishing_date']
verbose_name = "Articolo"
verbose_name_plural = "Articoli"
If you do this, all queries to this model will implicitly be ordered by -post_publishing_date. So this means that you can not "forget" to order the objects properly.
So then you do not have to order it in the views. You can of course only define one such "inherent" ordering, and it is not clear if you want to use one here.

order_by argument should be string:
queryset = PostModel.objects.filter().order_by('-post_publishing_date')

Lack of data with serialization model with ManyToManyField

Here's are examples I have:
models.py:
class Example(models.Model):
title = models.CharField(...)
description = models.CharField(...)
class Foo(models.Model):
example = models.ManyToManyField(Example)
serializers.py:
class FooSerializer(serializers.ModelSerializer):
class Meta:
model = Foo
fields = '__all__'
depth = 1
views.py:
...
serialized_data = [FooSerializer(foo).data for foo in Foo.objects.all().get]
In output, I receive only Example's IDs, but is there any way I could get title and description fields also (details of m2mfield)? As I understand, Foo.objects.all().get simply doesn't contain this data, but maybe I could somehow get it and use it?
I could also rebuild models if needed, but currently I use m2mf because of needs to contain multiple objects as related to this model data.
update
models.py:
class Event(models.Model):
ts = models.BigIntegerField(editable=False)
class Foo(Event):
user = models.ForeignKey(User, ...)
example = *...(remains to be the same)*
foos = models.ForeignKey('self', **somemore** null=True)
serializers.py:
class EventSerializer(serializers.ModelSerializer):
class Meta:
model = Event
fields = '__all__'
def to_representation(self, instance):
result = {'ts': instance.ts}
if isinstance(instance, Foo):
result['foo'] = FooSerializer(instance).data
return result
class UserSerializer(serializers.ModelSerializer):
class Meta:
model = User
fields = ('id', 'username')
class FooSerializer(serializers.ModelSerializer):
# user = UserSerializer(read_only=True) # with this I have an error: Got AttributeError when attempting to get a value for field 'username' on #serializer 'UserSerializer'
class Meta:
model = Foo
fields = '__all__'
depth = 1

You could use depth attribute to achieve desired output.
The default ModelSerializer uses primary keys for relationships, but
you can also easily generate nested representations using the depth
option.The depth option should be set to an integer value that
indicates the depth of relationships that should be traversed before
reverting to a flat representation.
class FooSerializer(serializers.ModelSerializer):
class Meta:
model = Foo
fields = '__all__'
depth = 1
Apart from the answer, I would like to change your views.py code, cause it seems like very bad :(. Do it on DRF Way as
serialized_data = FooSerializer(Foo.objects.all(), many=True).data<br>
Example View
from rest_framework.viewsets import ModelViewSet
class FooViewset(ModelViewSet):
serializer_class = FooSerializer
queryset = Foo.objects.all()
UPDATE-1
class UserSerializer(serializers.ModelSerializer):
class Meta:
model = User
exclude = ('password',) # add fields that are need to be excluded
class FooSerializer(serializers.ModelSerializer):
user = UserSerializer()
class Meta:
model = Foo
fields = '__all__'
depth = 1
depth = 1 will serializer all fields in the model, (It's same as setting the fields=='__all__' in Meta class of serializer)
UPDATE-2
class FooSerializer(serializers.ModelSerializer):
user = UserSerializer()
class Meta:
model = Foo
fields = '__all__'
depth = 1
def to_representation(self, instance):
real_data = super().to_representation(instance).copy()
# DO YOUR EXTRA CHECKS
child = UserSerializer(instance.child_foo).data
if child:
real_data.update({"child_data": child})
# After your checks, add it to "real_data"
return real_data
and I assumed I have a Foo model as
class Foo(models.Model):
example = models.ManyToManyField(Example)
user = models.ForeignKey(User)
child_foo = models.ForeignKey('self', null=True, blank=True)

In your serializer add depth = 1. Example where 'users' is the related field:
FooSerializer(serializers.ModelSerializer):
class Meta:
model = Foo
fields = ('id', 'account_name', 'users', 'created')
depth = 1

How to serialize a one to many relation in django-rest using Model serializer?

These are my models and serializers. I want a representation of Question Model along with a list of people the question was asked to.
I am trying this:
#api_view(['GET', 'PATCH'])
def questions_by_id(request,user,pk):
question = Question.objects.get(pk=pk)
if request.method == 'GET':
serializer = QuestionSerializer(question)
return Response(serializer.data)
But I get an empty dictionary ({}). However when I remove the asked field from QuestionSerializer I get a complete representation of Question along with Places serialized nicely. What am I missing ?
class AskedToSerializer(serializers.ModelSerializer):
class Meta:
model = AskedTo
fields = ('to_user', 'answered')
class QuestionSerializer(serializers.ModelSerializer):
class Meta:
model = Question
places = PlaceSerializer(many=True, required=False)
asked = AskedToSerializer(source='askedto_set', many=True)
fields = ('id', 'created_on', 'title', 'places', 'answered','asked')
extra_kwargs = {'created_by': {'read_only': True}}
class Question(BaseModel):
title = models.CharField(max_length=200, null=False)
places = models.ManyToManyField(Place, blank=True)
answered = models.BooleanField(default=False)
class AskedTo(BaseModel):
ques = models.ForeignKey(Question, on_delete=models.CASCADE)
to_user = models.ForeignKey(settings.AUTH_USER_MODEL)
replied = models.BooleanField(default=False)
class Place(models.Model):
g_place_id = models.CharField(max_length=20,primary_key=True)
json = models.TextField(null=True)
name = models.CharField(max_length=40)

I figured it out. There were two errors.
Changed this:
class AskedToSerializer(serializers.ModelSerializer):
class Meta:
model = AskedTo
fields = ('to_user', 'answered')
to this (notice the change in fields, fields on model and serializer didn't match)
class AskedToSerializer(serializers.ModelSerializer):
class Meta:
model = AskedTo
fields = ('to_user', 'replied')
Secondly, I needed to define any extra fields outside class Meta
class QuestionSerializer(serializers.ModelSerializer):
places = PlaceSerializer(many=True, required=False)
asked = AskedToSerializer(source='askedto_set', many=True)
class Meta:
model = Question
fields = ('id', 'created_on', 'title', 'places', 'answered','asked')
extra_kwargs = {'created_by': {'read_only': True}}
Notice the change in definition of places and asked.

In my case, I have this models.py:
class Section(models.Model):
title = models.CharField(max_length=500)
description = models.TextField(blank=True)
user = models.ForeignKey(Profile, related_name="sections", on_delete=models.CASCADE)
class Feed(models.Model):
title = models.CharField(max_length=500)
link_rss = models.URLField(max_length=500)
link_web = models.URLField(max_length=500)
description = models.TextField(blank=True)
language = models.CharField(max_length=50, blank=True)
logo = models.URLField(blank=True)
sections = models.ManyToManyField(Section, related_name="feeds")
And I completed the serializers.py this:
class FeedSerializer(serializers.ModelSerializer):
sections = serializers.PrimaryKeyRelatedField(many=True, read_only=True)
class Meta:
model = Feed
fields = '__all__'
class SectionSerializer(serializers.ModelSerializer):
feeds = FeedSerializer(many=True, read_only=True)
class Meta:
model = Section
exclude = ('user',)