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)
Related
Let's say we have three Models : ModelA, related to ModelB and ModelC.
ModelA is defined as :
class ModelA(models.Model):
field_b = models.ForeignKey(ModelB, on_delete=models.CASCADE)
field_c = models.ForeignKey(ModelC, on_delete=models.CASCADE)
other_field = models.CharField(max_length=30)
class Meta:
constraints = [
models.UniqueConstraint(fields=['field_b', 'field_c'], name='unique_modelA')
]
How to generate a ModelASerializer instance from instances of ModelB
and ModelC ?
Then, will there be a serialized representation of
field_b and field_c into ModelASerializer ?
The UniqueConstraint will
it be checked when calling .is_valid() onto ModelASerializer
instance ?
I tried the following :
class ModelASerializer(serializers.ModelSerializer):
field_b = ModelBSerializer(read_only=True)
field_c = ModelCSerializer(read_only=True)
other_field = serializers.CharField(required=False)
class Meta:
model = ModelA
fields = ('field_b', 'field_c', 'other_field',)
validators = [
UniqueTogetherValidator(
queryset=ModelA.objects.all(),
fields=['field_b', 'field_c'],
message='A Model A instance for this couple of ModelB and ModelC instances already exists.'
)
]
def create(self, validated_data):
"""
Create and return a new `ModelA` instance, given the validated data.
"""
return ModelA.objects.create(**validated_data)
def update(self, instance, validated_data):
"""
Update and return an existing `ModelA` instance, given the validated data.
"""
instance.other_field= validated_data.get('other_field', instance.other_field)
instance.save()
return instance
But I cannot find any way to create the serializer :
model_b = ModelB()
model_c = ModelC()
model_b.save()
model_c.save()
other_field = "Dummy content"
First try
model_a_serializer = ModelASerializer(model_b, model_c, other_field)
The serializer is looking for an ID field and can't find it
Anyway, no data field being provided, we can't call .is_valid() onto the serializer, and thus, can't check the integrity constraint
Second try
model_b_serializer = ModelBSerializer(model_b)
model_c_serializer = ModelCSerializer(model_c)
data = {'model_b':model_b_serializer , 'model_c':model_c_serializer , 'other_field':other_field}
model_a_serializer = ModelASerializer(data=data)
if model_a_serializer.is_valid():
model_a_serializer.save()
Here, the serializer tries to recreate the ModelB and ModelC instances when is_valid() is called... And I don't want that.
Any ideas? Thank you very much by advance.
Not sure if I understood your question properly but...
How to generate a ModelASerializer instance from instances of ModelB and ModelC ?
If you want to generate a ModelA instance from ModelB and ModelCthen you should remove read_only=True argument and you have to explictly specify the relationship in create and update method.
class ModelBSerializer(serializers.ModelSerializer):
modelA_set = ModelASerializer() # this field name can be changed by adding related_name attribute in ModelA in models.py
class Meta:
model = ModelB
fields = ('modelA_set' , 'other_fields')
def create(self,validate_data):
modelA_data = validate_data.pop('modelA_data') # whatever field name you will use to send data for modelA
b = ModelB.objects.create(**validate_data)
for data in modelA_data:
modelA_instance = ModelA.objects.create(field_b=b ,**data)
return b
modelA_set is an automatically generated field name when we are trying to serialize ModelA from ModelB serializer . It can be changed by passing related_name='some_name' argument like this:
field_b = models.ForeignKey(ModelB, on_delete=models.CASCADE , related_name="field_a")
Then, will there be a serialized representation of field_b and field_c into ModelASerializer ?
Yes there will be.
Again correct me if I misunderstood your question.
I have a model which contains sensitive data, let's say a social security number, I would like to transform that data on serialization to display only the last four digits.
I have the full social security number stored: 123-45-6789.
I want my serializer output to contain: ***-**-6789
My model:
class Employee (models.Model):
name = models.CharField(max_length=64,null=True,blank=True)
ssn = models.CharField(max_length=16,null=True,blank=True)
My serializer:
class EmployeeSerializer(serializers.ModelSerializer):
id = serializers.ReadOnlyField()
class Meta:
model = Employee
fields = ('id','ssn')
read_only_fields = ['id']
You can use SerializerMethodField:
class EmployeeSerializer(serializers.ModelSerializer):
id = serializers.ReadOnlyField()
ssn = SerializerMethodField()
class Meta:
model = Employee
fields = ('id','ssn')
read_only_fields = ['id']
def get_ssn(self, obj):
return '***-**-{}'.format(obj.ssn.split('-')[-1]
If you don't need to update the ssn, just shadow the field with a SerializerMethodField and define get_ssn(self, obj) on the serializer.
Otherwise, the most straightforward way is probably to just override .to_representation():
def to_representation(self, obj):
data = super(EmployeeSerializer, self).to_representation(obj)
data['ssn'] = self.mask_ssn(data['ssn'])
return data
Please add special case handling ('ssn' in data) as necessary.
Elaborating on #dhke’s answer, if you want to be able to reuse this logic to modify serialization across multiple serializers, you can write your own field and use that as a field in your serializer, such as:
from rest_framework import serializers
from rest_framework.fields import CharField
from utils import mask_ssn
class SsnField(CharField):
def to_representation(self, obj):
val = super().to_representation(obj)
return mask_ssn(val) if val else val
class EmployeeSerializer(serializers.ModelSerializer):
ssn = SsnField()
class Meta:
model = Employee
fields = ('id', 'ssn')
read_only_fields = ['id']
You can also extend other fields like rest_framework.fields.ImageField to customize how image URLs are serialized (which can be nice if you’re using an image CDN on top of your images that lets you apply transformations to the images).
I have this code
# Models
class NestedSample(models.Model):
something = models.CharField(max_length=255)
class Sample(models.Model):
thing = models.BooleanField()
nested = models.ForeignKey(NestedSample)
# Serializers
class NestedSampleSerializer(serializers.HyperlinkedModelSerializer):
class Meta:
model = api_models.NestedSample
class SampleSerializer(serializers.HyperlinkedModelSerializer):
nested = NestedSampleSerializer() # HERE filter delete=false
nested2 = NestedSample2Serializer() # HERE filter deletefalse
class Meta:
model = api_models.Sample
In my view I am overrding the queryset for delete=False but it is not applying to nested serializers.
delete=False in queryset will only filter Sample. To filter queryset in nested serializer you can use serializers.ListSerializer like:
class FilterDeleteListSerializer(serializers.ListSerializer):
def to_representation(self, data):
data = data.filter(delete=False)
return super(FilterDeleteListSerializer, self).to_representation(data)
class NestedSampleSerializer(serializers.HyperlinkedModelSerializer):
class Meta:
model = api_models.NestedSample
list_serializer_class = FilterDeleteListSerializer
class NestedSample2Serializer(serializers.HyperlinkedModelSerializer):
class Meta:
model = api_models.NestedSample2
list_serializer_class = FilterDeleteListSerializer
class SampleSerializer(serializers.HyperlinkedModelSerializer):
nested = NestedSampleSerializer() # HERE filter delete=false
nested2 = NestedSample2Serializer() # HERE filter deletefalse
class Meta:
model = api_models.Sample
Learn more here
I didn't exactly understand your question, but from what I figured you've got a boolean field in your Model which is set to True if you delete the object instead of actually deleting it from the database (SQL DELETE).
Now coming to your question, if you just want to filter the nested serializer then you could use the SerializerMethodField. You need to specify the method to call as an argument or add a method with the name 'get_' followed by the field name. In this method you can filter the queryset serialize it and return the data of that queryset.
class UserSerializer(serializers.ModelSerializer):
delete_filtered_items = serializers.SerializerMethodField()
class Meta:
model = User
def get_delete_filtered_items(self, obj):
items = Item.objects.filter(user=obj,deleted=False)
serializer = ItemsSerializer(instance=items, many=True)
return serializer.data
The above solution should work for your requirements, but if what you've implemented is similar to a soft delete then it would seem cleaner and more moduler to create a custom model manager.
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
I have used Django Filters successfully before to filter models like so:
class ProductFilter(django_filters.FilterSet):
minCost = django_filters.NumberFilter(name="cost", lookup_type='gte')
maxCost = django_filters.NumberFilter(name="cost", lookup_type='lte')
class Meta:
model = Product
fields = ['name', 'minPrice', 'maxPrice', 'manufacturer',]
Now I want to use a Django Filter to filter between many different models which all inherit from a base model, for example (my models are not this simple but to illustrate the point):
class BaseProduct(models.Model):
name = models.CharField(max_length=256)
cost = models.DecimalField(max_digits=10,decimal_places=2)
class FoodProduct(BaseProduct):
farmer = models.CharField(max_length=256)
class ClothingProduct(BaseProduct):
size = models.CharField(max_length=256)
Is there a way to use a Django filter that would work with all models that inherit from BaseProduct? In my case there would be a large number of models some with a large number of variables.
Add to your BaseProduct
class Meta:
abstract = True
https://docs.djangoproject.com/en/dev/topics/db/models/#abstract-base-classes
Base model will not be used to create any database table. Instead, when it is used as a base class for other models, its fields will be added to those of the child class.
https://django-filter.readthedocs.org/en/latest/usage.html#the-filter
Just like with a ModelForm we can also override filters, or add new ones using a declarative syntax
class BaseProductFilter(django_filters.FilterSet):
name = django_filters.CharFilter(lookup_type='icontains')
cost = django_filters.NumberFilter(lookup_type='lt')
class FoodProductFilter(BaseProductFilter):
farmer = django_filters.CharFilter(lookup_type='icontains')
class Meta:
model = FoodProduct
fields = ['name', 'cost', 'farmer']
class ClothingProductFilter(BaseProductFilter):
# size lookup_type will be 'exact'
class Meta:
model = ClothingProduct
fields = ['name', 'cost', 'size']