Let's say I have models like this:
class A(models.Model):
...some fields here
class B(models.Model):
...some fields here
a = models.ForeignKey(A, on_delete=CASCADE)
class C(models.Model):
...some fields here
b = models.ForeignKey(B, on_delete=CASCADE)
...
And I want my API endpoint to return something like this
{
...some fields here
b: [
{
...some field here
c: [{...}, {...} ...]
},
{
...some field here
c: [{...}, {...} ...]
}
...
]
}
I know I can do something like this:
class Bserializer(serializers.ModelSerializer):
c = Cserializer(source="c_set", many=True, read_only=True,)
class Meta:
model = B
fields = [...some fields, "c"]
class Aserializer(serializers.ModelSerializer):
b = Bserializer(source="b_set", many=True, read_only=True,)
class Meta:
model = A
fields = [...some fields, "b"]
But if this goes deeper or/and models have more foreign keys it starts to become really complicated. Is there a way to add recursively all instances referencing the model.
You can specify a depth value in the serializer Meta class, however, this won't' work if you want to customize any part of the nested data, as this will automatically create model serializers (with all fields) for nested relations. Check docs here
class Aserializer(serializers.ModelSerializer):
class Meta:
model = A
fields = [...some fields, "b"]
depth = 2
The bottom line, if you don't do any customization of the nested serializers, use it, otherwise, stick with custom serializers for each of the relations. But I'll suggest keeping the nested data at a minimum as it will impact performance
Related
I have 2 models
class Tag(models.Model):
id = models.AutoField(primary_key=True)
name = models.CharField(max_length=255)
def __str__(self):
return self.name
class Question(models.Model):
ques_id = models.IntegerField(default=0)
name = models.CharField(max_length=255)
Tag_name = models.ManyToManyField(Tag)
class Meta:
ordering = ['ques_id']
def __str__(self):
return self.name
searlizers.py
class TagSerializers(serializers.ModelSerializer):
class Meta:
model = Tag
fields = '__all__'
class QuestionSerializers(serializers.ModelSerializer):
class Meta:
model = Question
fields = '__all__'
This is my searilzers class.
I want the response like
{
"id": 1,
"name": "QUES 1",
"tags": [{
"id": 1,
"name": "Abcd"
}]
}
what will be query to get Fetch 10 questions, given some input tag ids
e.g Tag_id = 1 or 2 or 3.
You need to add tags field as another serializer data to your QuestionSerializer.
Your QuestionSerializer code should look like that:
class QuestionSerializers(serializers.ModelSerializer):
Tag_name = TagSerializer(many=True)
class Meta:
model = Question
fields = '__all__'
If you want exactly tags name in response, you can specify SerializerMethodField like that:
class QuestionSerializer(serializers.ModelSerializer):
tags = serializers.SerializerMethodField()
get_tags(self, instance):
return TagSerializer(instance.Tag_name, many=True).data
class Meta:
model = Question
fields = ('ques_id', 'name', 'tags')
First: I would suggest that you refactor your Question Model, since it has a ques_id, and I think it is considered a duplicate (since Django already creates an id field by default)
Then You need to change your ManyToManyField's name to tags, and makemigrations, then migrate
class Question(models.Model):
name = models.CharField(max_length=255)
tags = models.ManyToManyField(Tag)
class Meta:
ordering = ['id']
def __str__(self):
return self.name
# run make migrations
python manage.py makemigrations <<<YOUR QUESTIONS APP NAME>>>
# It will prompt you to check if you change the many to many relationship say yes
Did you rename question.Tag_name to question.tags (a ManyToManyField)? [y/N] y
# Then Run migrate
python manage.py migrate
Second: Update your QuestionSerializers to make the tags field serialize the relation
class QuestionSerializers(serializers.ModelSerializer):
tags = TagSerializers(many=True)
class Meta:
model = Question
fields = '__all__'
This way you make your code cleaner. And you are good to go.
Answer Updated (Filtering, and Pagination)
Now if you wanted to filter questions based on provided tag ids.
You need to use PageNumberPagination for your view, and for filtering use DjangoFilterBackend.
I recommend you to make them the default of DRF settings.
Make sure you have django-filter installed.
# In your settings.py
REST_FRAMEWORK = {
'DEFAULT_PAGINATION_CLASS': 'rest_framework.pagination.PageNumberPagination',
'DEFAULT_FILTER_BACKENDS': (
'django_filters.rest_framework.DjangoFilterBackend',
),
'PAGE_SIZE': 10
}
Now create your custom filter
# Inside filters.py
import re
import django_filters
from questions.models import Question
class QuestionsFilterSet(django_filters.FilterSet):
tags = django_filters.CharFilter(field_name='tags__id', method='tags_ids_in')
def tags_ids_in(self, qs, name, value):
ids_list = list(map(lambda id: int(id), filter(lambda x: x.isdigit(), re.split(r'\s*,\s*', value))))
return qs.filter(**{f"{name}__in": ids_list}).distinct()
class Meta:
model = Question
fields = ('tags',)
Now use ListAPIView to list your questions
class QuestionsListAPIView(ListAPIView):
queryset = Question.objects.all()
serializer_class = QuestionSerializers
filter_class = QuestionsFilterSet
Now if you hit
http://<PATH_TO_VIEW>?tags=1,2,3
You will receive all Questions that have tag id 1, 2, or 3.
and all of them will be paginated 10 results at a time.
You just need to write a field tags like this in your QuestionSerializers
class QuestionSerializers(serializers.ModelSerializer):
tags = TagSerializers(source='Tag_name', many=True)
class Meta:
model = Question
fields = ('id', 'name', 'tags')
It will give you response like this
{
"id": 1,
"name": "QUES 1",
"tags": [{
"id": 1,
"name": "Abcd"
}]
}
Your query to fetch on the basis of tags will be like this
Question.objects.filter(Tag_name__in=[1, 2, 4])
Is there a way to group fields in Serializer/ModelSerializer or to modify JSON structure?
There is a Location model:
class Location(Model):
name_en = ...
name_fr = ...
...
If I use ModelSerializer I get plain representation of the object fields like:
{'name_en':'England','name_fr':'Angleterre'}
I want to group some fields under "names" key so I get
{'names':{'name_en':'England','name_fr':'Angleterre'}}
I know I can create custom fields but I want to know if there is a more straightforward way. I tried
Meta.fields = {'names':['name_en','name_fr']...}
which doesn't work
I think it is better using a property. Here is the whole example.
class Location(models.Model):
name_en = models.CharField(max_length=50)
name_fr = models.CharField(max_length=50)
#property
def names(self):
lst = {field.name: getattr(self, field.name)
for field in self.__class__._meta.fields
if field.name.startswith('name_')}
return lst
In views:
class LocationViewSet(viewsets.ModelViewSet):
model = models.Location
serializer_class = serializers.LocationSerializer
queryset = models.Location.objects.all()
And in serializers:
class LocationSerializer(serializers.ModelSerializer):
class Meta:
model = Location
fields = ('id', 'names')
My result for my fake data:
[{
"id": 1,
"names": {
"name_en": "England",
"name_fr": "Angleterre"}
}]
Try to create a wrapper serialzer and place the LocationSerializer inside it
class LocationSerialzer(serializers.ModelSerialzer):
name_en = ...
name_fr = ...
...
class MySerializer(serializers.ModelSerializer):
name = LocationSerialzer()
...
Using the above method , you can apply your own customization without being limited to drf custom fields.
You could also not use a property on the model and but use a SerializerMethodField on your serializer like in this implementation.
We used here a _meta.fields, like in the other implementation, to get all the fields that starts with name_ so we can dynamically get the output you desired
class LocationSerializer(serializers.ModelSerializer):
names = serializers.SerializerMethodField()
def get_names(self, obj):
lst = {field.name: getattr(obj, field.name)
for field in obj.__class__._meta.fields
if field.name.startswith('name_')}
return lst
class Meta:
model = Location
fields = ('id', 'names')
I have two serializers with same model. I want to nest them.
Unfortunately this approach does not work:
class BookSerializer(serializers.ModelSerializer):
class Meta:
model = Book
fields = ['name', 'word_count']
class BetterBookSerializer(serializers.ModelSerializer):
book = BookSerializer(many=False)
class Meta:
model = Book
fields = ('id', 'book')
Expected result:
{
"id": 123,
"book": {
"name": "book_name",
"word_count": 123
}
}
Use source=* instead of many=True as
class BetterBookSerializer(serializers.ModelSerializer):
book = BookSerializer(source='*')
class Meta:
model = Book
fields = ('id', 'book')
From the doc,
The value source='*' has a special meaning, and is used to indicate that the entire object should be passed through to the field. This can be useful for creating nested representations, or for fields which require access to the complete object in order to determine the output representation.
You can achieve the desired output like this:
class BookSerializer(serializers.ModelSerializer):
class Meta:
model = Book
fields = ['name', 'word_count']
class BetterBookSerializer(serializers.ModelSerializer):
book = serializers.SerializerMethodField(read_only=True)
class Meta:
model = Book
fields = ('id', 'book')
def get_book(self, obj):
return BookSerializer(obj).data
Small Update:
Although my approach to solve your problem works just fine, the answer from #JPG mentioning source='*' option is a good way to go. In that way you can easily use the nested serializer when creating new object.
My design is as following about Django ModelSerializer.
There are model A and model B. Model B has a foreign key field of Model A. For some reasons, I can not use the primary key directly to serialize Model B. As my thought, what I need is to serialize two other fields(unique together in Model A).
And I see the SlugRelatedField must be used for one slug field.
I searched there is a NaturalKeyField can support NaturalKeyField. But it looks like it is superseeded by django-rest-framework. But I checked the django-rest-framework, there is no such field at all.
Can anyone help?? What should I do?
The code is as following.
Model A
class AssetModel(models.Model):
org = models.ForeignKey(Org, related_name='models')
name = models.CharField(max_length=128)
model_type = models.SmallIntegerField(default = 3,choices = MODEL_TYPE )
directory = models.CharField(max_length = 128)
...
class Meta:
unique_together = ('org', 'name',)
Model B
class Dataitem(models.Model):
mod = models.ForeignKey(AssetModel, related_name='dataitems')
name = models.CharField(max_length=128)
data_type = models.SmallIntegerField(default =0,choices = DATAITEM_DATATYPE)
...
Serializer of model A
class AssetModelSerializer(serializers.ModelSerializer):
org = serializers.SlugRelatedField(queryset=Org.objects.all(), slug_field='name')
class Meta:
model = AssetModel
fields = ('org', 'name', 'model_type',..
Serializer of model B
class DataitemSerializer(serializers.ModelSerializer):
class Meta:
model = Dataitem
fields = ('mod', 'name','data_type'...)
The primary key of Model A is just a id Django auto added. When serialize the model B, I need to get the org and name of model A. Both read and write are needed.
Nested Serializer
You can do something like this, define a serializer for Dataitem that can reuse a serializer of the AssetModel model
class AssetModelSerializer(serializers.ModelSerializer):
class Meta:
model = AssetModel
# Fields org and name of AssetModel will be inlcuded by default
class DataitemSerializer(serializers.ModelSerializer):
class Meta:
model = Dataitem
mod = AssetModelSerializer()
# This is the Dataitem.mod field
# which is a FK to AssetModel,
# Now it'll be serilized using the AssetModelSerializer
# and include the org and name fields of AssetModelSerializer
I prefer this approach because of the control I get.
If you serialize using the above you get a structure like this:
data_item = {'name': ..., 'mod': {'org': ..., 'name': ...}}
^
|___ AssetModel fields
Alternatively you can also use depth = n
You can also use depth = 1 in Dataitem
class DataitemSerializer(serializers.ModelSerializer):
class Meta:
model = Dataitem
depth = 1 # Will include fields from related models
# e.g. the mod FK to AssetModel
Writable Nested Serializer
Because the behavior of nested creates and updates can be ambiguous,
and may require complex dependencies between related models, REST
framework 3 requires you to always write these methods explicitly.
We have to implement create/update to make this writable as per DRF's documentation
class DataitemSerializer(serializers.ModelSerializer):
class Meta:
model = Dataitem
# Nested serializer
mod = AssetModelSerializer()
# Custom create()
def create(self, validated_data):
# First we create 'mod' data for the AssetModel
mod_data = validated_data.pop('mod')
asset_model = AssetModel.objects.create(**mod_data)
# Now we create the Dataitem and set the Dataitem.mod FK
dataitem = Dataitem.objects.create(mod=asset_model, **validated_data)
# Return a Dataitem instance
return dataitem
There seems to be a library that does this
drf-writable-nested
it handles the creation and serialisation of these types
OneToOne (direct/reverse)
ForeignKey (direct/reverse)
ManyToMany (direct/reverse excluding m2m relations with through model)
GenericRelation (this is always only reverse)
I have some models like these:
class TypeBase(models.Model):
name = models.CharField(max_length=20)
class Meta:
abstract=True
class PersonType(TypeBase):
pass
class CompanyType(TypeBase):
pass
Having this, I want to create just one serializer that holds all these field types (serialization, deserialization, update and save).
To be more specific, I want only one serializer (TypeBaseSerializer) that print the Dropdown on the UI, serialize the json response, deserialize it on post and save it for all my based types.
Something like this:
class TypeBaseSerializer(serializers.Serializer):
class Meta:
model = TypeBase
fields = ('id', 'name')
Is it possible?
I think the following approach is more cleaner. You can set "abstract" field to true for the base serializer and add your common logic for all child serializers.
class TypeBaseSerializer(serializers.ModelSerializer):
class Meta:
model = TypeBase
fields = ('id', 'name')
abstract = True
def func(...):
# ... some logic
And then create child serializers and use them for data manipulation.
class PersonTypeSerializer(TypeBaseSerializer):
class Meta:
model = PersonType
fields = ('id', 'name')
class CompanyTypeSerializer(TypeBaseSerializer):
class Meta:
model = CompanyType
fields = ('id', 'name')
Now you can use the both of these serializers normally for every model.
But if you really want to have one serializers for both the models, then create a container model and a serializer for him too. That is much cleaner :)
You can't use a ModelSerializer with an abstract base model.
From restframework.serializers:
if model_meta.is_abstract_model(self.Meta.model):
raise ValueError(
'Cannot use ModelSerializer with Abstract Models.'
)
I wrote a serializer_factory function for a similar problem:
from collections import OrderedDict
from restframework.serializers import ModelSerializer
def serializer_factory(mdl, fields=None, **kwargss):
""" Generalized serializer factory to increase DRYness of code.
:param mdl: The model class that should be instanciated
:param fields: the fields that should be exclusively present on the serializer
:param kwargss: optional additional field specifications
:return: An awesome serializer
"""
def _get_declared_fields(attrs):
fields = [(field_name, attrs.pop(field_name))
for field_name, obj in list(attrs.items())
if isinstance(obj, Field)]
fields.sort(key=lambda x: x[1]._creation_counter)
return OrderedDict(fields)
# Create an object that will look like a base serializer
class Base(object):
pass
Base._declared_fields = _get_declared_fields(kwargss)
class MySerializer(Base, ModelSerializer):
class Meta:
model = mdl
if fields:
setattr(Meta, "fields", fields)
return MySerializer
You can then use the factory to produce serializers as needed:
def typebase_serializer_factory(mdl):
myserializer = serializer_factory(
mdl,fields=["id","name"],
#owner=HiddenField(default=CurrentUserDefault()),#Optional additional configuration for subclasses
)
return myserializer
Now instanciate different subclass serializers:
persontypeserializer = typebase_serializer_factory(PersonType)
companytypeserializer = typebase_serializer_factory(CompanyType)
As already mentioned in Sebastian Wozny's answer, you can't use a ModelSerializer with an abstract base model.
Also, there is nothing such as an abstract Serializer, as some other answers have suggested. So setting abstract = True on the Meta class of a serializer will not work.
However you need not use use a ModelSerializer as your base/parent serializer. You can use a Serializer and then take advantage of Django's multiple inheritance. Here is how it works:
class TypeBaseSerializer(serializers.Serializer):
# Need to re-declare fields since this is not a ModelSerializer
name = serializers.CharField()
id = serializers.CharField()
class Meta:
fields = ['id', 'name']
def someFunction(self):
#... will be available on child classes ...
pass
class PersonTypeSerializer(TypeBaseSerializer, serializers.ModelSerializer):
class Meta:
model = PersonType
fields = TypeBaseSerializer.Meta.fields + ['another_field']
class CompanyTypeSerializer(TypeBaseSerializer, serializers.ModelSerializer):
class Meta:
model = CompanyType
fields = TypeBaseSerializer.Meta.fields + ['some_other_field']
So now since the fields name and id are declared on the parent class (TypeBaseSerializer), they will be available on PersonTypeSerializer and since this is a child class of ModelSerializer those fields will be populated from the model instance.
You can also use SerializerMethodField on the TypeBaseSerializer, even though it is not a ModelSerializer.
class TypeBaseSerializer(serializers.Serializer):
# you will have to re-declare fields here since this is not a ModelSerializer
name = serializers.CharField()
id = serializers.CharField()
other_field = serializers.SerializerMethodField()
class Meta:
fields = ['id', 'name', 'other_field']
def get_other_field(self, instance):
# will be available on child classes, which are children of ModelSerializers
return instance.other_field
Just iterating a bit over #adki's answer:
it is possible to skip model for TypeBaseSerializer;
derived serializers can refer to TypeBaseSerializer.Meta, so you would change them in a single place.
class TypeBaseSerializer(serializers.Serializer):
class Meta:
fields = ('id', 'name', 'created')
abstract = True
def func(...):
# ... some logic
class PersonTypeSerializer(TypeBaseSerializer):
class Meta:
model = PersonType
fields = TypeBaseSerializer.Meta.fields + ('age', 'date_of_birth')
class CompanyTypeSerializer(TypeBaseSerializer):
class Meta:
model = CompanyType
fields = TypeBaseSerializer.Meta.fields