Develop Reference

Django ViewSet, get data from model without foreign key

My Models
def ModelA(models.Model):
id = models.CharField(primary_key=True, max_length=50)
val_a = models.CharField(db_index=True, max_length=100)
val_b = models.CharField(db_index=True, max_length=100)
modelB = models.ForeignKey(modelB, on_delete=models.CASCADE, db_constraint=False)
def ModelB(models.Model):
id = models.CharField(primary_key=True, max_length=50)
val_c = models.CharField(db_index=True, max_length=100)
val_d = models.CharField(db_index=True, max_length=100)
def ModelC(PostgresModel):
id = models.CharField(primary_key=True, max_length=50)
val_e = models.CharField(db_index=True, max_length=100)
modelB = models.OneToOneField(ModelB, on_delete=models.CASCADE, null=False, blank=False)
My ViewSet
class ModelAViewSet(ListDataResponseMixin, APIKeyViewSet):
endpoint_permissions = [APILicenseKeyPermission.Codes.A]
queryset = ModelA.objects.all()
serializer_class = ModelASerializer
filterset_class = ModelAFilter
filter_backends = [DjangoFilterBackend]
My Serializer
class ModelASerializer(serializers.ModelSerializer):
class Meta:
model = ModelA
fields = (
"id",
"val_a",
"val_b"
)
When querying ModelA I would like to get val_e from ModelC. I am learning django, and previously when I needed to do something like this, I would use select_related, however, since there is no clear path from ModelA -> ModelC using foreign keys, I am not sure how to proceed. (My base models cannot change). How would I modify my ViewSet to include the needed ModelC data in my queryset? And then for my ModelASerializer I would like to just be able to add in val_e.

You can simply use a CharField, like this:
class ModelASerializer(serializers.ModelSerializer):
val_e = serializers.CharField(source='modelB.modelc.val_e')
class Meta:
model = ModelA
fields = (
"id",
"val_a",
"val_b",
"val_e"
)
This is possible because ModelA has a ForeignKey to ModelB and ModelB has One To One relation to ModelC. More information on source can be found in documentation.

Unable to POST JSON data from multiple select element with Django REST Framework

I would like to be able to send an AJAX POST request to my API endpoint to create a new instance of my Asset model with multiple Category instances referenced in my Asset model, hence the many-to-many field type in my Asset model.
I'm able to successfully POST and create new Asset instances, however my category field won't accept any data at all. The category field remains empty when a new Asset instance is created. I think it has something to do with my CategorySerializer. I'm still learning how to use Django REST Framework so I'd appreciate if I could get some help figuring out how to work with serializers in Django REST Framework.
I've already tried modifying the AssetSerializer create method to handle parsing the JSON and validating the data but that hasn't worked. I've also tried other solutions suggested in other posts I've found on StackOverflow but haven't found anything that works for my situation.
Here's my serializers.py file:
class CategorySerializer(serializers.ModelSerializer):
name = serializers.CharField(required=False, read_only=True)
class Meta:
model = Category
fields = ('id', 'name')
class AssetSerializer(serializers.ModelSerializer):
name = serializers.CharField(allow_null=True)
description = serializers.CharField(allow_null=True)
manufacturer = serializers.CharField(allow_null=True)
uid = serializers.UUIDField(read_only=True, allow_null=True)
borrower = BorrowerSerializer(allow_null=True, read_only=True)
condition = serializers.ChoiceField(choices=Asset.CONDITION_TYPE, default='g', allow_null=True)
owner = serializers.ReadOnlyField(source='owner.username')
return_date = serializers.DateField(allow_null=True)
checked_out = serializers.BooleanField(allow_null=True)
category = CategorySerializer(required=False, many=True)
class Meta:
model = Asset
fields = ('uid',
'name',
'manufacturer',
'model',
'description',
'owner',
'condition',
'category',
'borrower',
'checked_out',
'return_date',
'is_dueback',
)
def update(self, instance, validated_data):
instance.borrower = validated_data.get('borrower', instance.borrower)
instance.return_date = validated_data.get('return_date', instance.return_date)
instance.checked_out = validated_data.get('checked_out', instance.checked_out)
instance.name = validated_data.get('name', instance.name)
instance.manufacturer = validated_data.get('manufacturer', instance.manufacturer)
instance.model = validated_data.get('model', instance.model)
instance.description = validated_data.get('description', instance.description)
instance.condition = validated_data.get('condition', instance.condition)
instance.category = validated_data.get('category', instance.category)
instance.save()
return instance
def create(self, validated_data):
return Asset.objects.create(**validated_data)
Here's my Asset model:
class Asset(models.Model):
"""Model representing an Asset"""
uid = models.UUIDField(primary_key=True, default=uuid.uuid4)
name = models.CharField(max_length=200)
manufacturer = models.CharField(max_length=64)
model = models.CharField(max_length=128)
description = models.TextField()
category = models.ManyToManyField(Category)
owner = models.ForeignKey(settings.AUTH_USER_MODEL, on_delete=models.CASCADE)
borrower = models.ForeignKey(Borrower, on_delete=models.CASCADE, null=True, blank=True)
checked_out = models.BooleanField(default=False)
return_date = models.DateField(null=True, blank=True)
CONDITION_TYPE = (
('e', 'Excellent'),
('g', 'Good'),
('f', 'Fair'),
('p', 'Poor'),
)
condition = models.CharField(
max_length=1,
choices=CONDITION_TYPE,
blank=True,
help_text='Asset condition')
class Meta:
ordering = ['return_date']
#property
def is_dueback(self):
if self.return_date and date.today() > self.return_date:
return True
return False
def display_category(self):
"""Create a string for the Category. This is required to display category in Admin."""
return ', '.join(category.name for category in self.category.all())
display_category.short_description = 'Category'
def __str__(self):
return f'{self.uid} - {self.name}'
def get_absolute_url(self):
return reverse('asset-detail', args=[str(self.uid)])
Here's my Category model:
class Category(models.Model):
"""Model representing an Asset category"""
name = models.CharField(max_length=128)
def __str__(self):
return self.name
I'd appreciate any help you could provide. Thank you in advance.

i'm almost new in DRF but i try to help. why you writing all the field in serializer when you using ModelsSerializer? not need to telling ModelSerializer what type of field should be because you are pointing to model in class Meta and DRF know about fields and type and etc . second about allow_null=True in serializer, when Model haven't null=True you can't except DRF can create a not null-able field for instance with null=True so if you wnt a field can be null just add null=True in Model class . for your problem about ManytoMantry field try to use Primary key relation for ManyToMany fields in your serializers then pass id of Category instances in list:
class AssetSerializer(serializers.ModelSerializer):
borrower = BorrowerSerializer(allow_null=True, read_only=True)
category = serializers.PrimaryKeyRelatedField(many=True, queryset=Category.objects.all())
class Meta:
model = Asset
fields = ('uid',
'name',
'manufacturer',
'model',
'description',
'owner',
'condition',
'category',
'borrower',
'checked_out',
'return_date',
'is_dueback',
)
read_only_fields = ( 'uid' , ) # this fields will be read_only
depending on how you using this serializer in your view for save and update have difference way. if your view is generics class so will do create and update itself by POST and PUT method .and for other class view that isn't belong to generics DRF view you can using serializer.save() to create a new instance.wish help you.
pass data something like:
{
"name" : "foo",
"manufacture" : "foo",
.
.
.
"category" : [1,2,3,24,65]
}

Many to Many model with a dropdown in Django Rest Framework?

I am trying to create a Many to Many relation with a model in between, I have a Client model, and a Zone model, each client may have access to different zones, and each zone may have multiple clients.
Therefore I created a model called Access Permission, that stores said relation, and I want to show a dropdown selector in the post form that shows the existing clients and zones, or to ask for the Id of an existing object, instead of showing the form to create new ones.
These are my models:
class Zone(models.Model):
name = models.TextField()
created = models.DateTimeField(auto_now=True)
def __str__(self):
return '%s' % (self.name)
class Client(models.Model):
name = models.TextField()
birthDate = models.DateField()
created = models.DateTimeField(auto_now=True)
def __str__(self):
return '%s' % (self.name)
class AccessPermission(models.Model):
idClient = models.ForeignKey(Client, on_delete=models.CASCADE, null=False)
idZone = models.ForeignKey(Zone, on_delete=models.CASCADE, null=False)
And these my current serializers:
class ZoneSerializer(serializers.HyperlinkedModelSerializer):
class Meta:
model = Zone
fields = ('name',)
class ClientSerializer(serializers.HyperlinkedModelSerializer):
zones = ZonesSerializer(source='accesspermission_set', many=True, read_only=True)
class Meta:
model = Client
fields = ('name', 'birthDate', 'zones')
class AccessPermissionSerializer(serializers.ManyRelatedField):
idClient = ClientSerializer(many=False)
idZone = ZoneSerializer(many=False)
class Meta:
model = AccessPermission
fields = ('idClient', 'idZone')
Is there any way to ask for the Id of an existing object, or show the existing ones, instead of the fields to create new ones?

You can do it like:
models
class AccessPermission(models.Model):
client = models.ForeignKey(Client, on_delete=models.CASCADE, null=False)
zone = models.ForeignKey(Zone, on_delete=models.CASCADE, null=False)
serializers
class AccessPermissionSerializer(serializers.ManyRelatedField):
id = serializers.IntegerField(read_only=True)
client_id = serializers.PrimaryKeyRelatedField(
queryset=Client.objects.all(), source='client', allow_null=False, required=True
)
zone_id = serializers.PrimaryKeyRelatedField(
queryset=Zone.objects.all(), source='zone', allow_null=False, required=True
)
class Meta:
model = AccessPermission
fields = (
'id', 'client_id', 'zone_id'
)

Django rest framework serializer with reverse relation

I have two models where employee have relation with person model but person have no relation with employee model.
Like:
class Person(models.Model):
name = models.CharField(max_length=100)
address = models.CharField(max_length=100)
class Employee(models.Model):
person = models.ForeignKey(Person, related_name='person_info')
code = models.CharField()
In such cases I want code field data in person serializer.
I can solved this with writing method in person model or using SerializerMethodField in person serializer
like this:
def get_employee_code(self):
return Employee.objects.get(person=self).id
and add this as source in person serializer
employee_code = serializers.CharField(source='get_employee_code')
Or adding employee serializer into person serialiszer
class PersonSerializer(serializers.ModelSerializer):
employee = EmployeeSerializer()
class Meta:
model = Person
fields = ('name', 'address', 'employee')
But i was trying to do this with reverse relation but i can't. I have tried like this, it gives an error
Serializer:
class PersonSerializer(serializers.ModelSerializer):
employee_code = serializers.CharField(source='person_info.code')
class Meta:
model = Person
fields = ('name', 'address', 'employee_code')
How can i solve this with reverse relation?

At the moment because you are using a ForeignKey field on the person attribute, it means that its returning a list when you access the reverse relation.
One solution would be to use a slug related field, though this must have many and read_only set to True, and will return a list because of the ForeignKey field.
class PersonSerializer(serializers.ModelSerializer):
employee_code = serializers.SlugRelatedField(
source='person_info',
slug_field='code',
many=True,
read_only=True,
)
class Meta:
model = Person
fields = ('name', 'address', 'employee_code')
The other option is to change your ForeignKey into a OneToOneField, which would still need read_only set to True but it will not return a list.
class Person(models.Model):
name = models.CharField(max_length=100)
address = models.CharField(max_length=100)
class Employee(models.Model):
person = models.OneToOneField(Person, related_name='person_info')
code = models.CharField()
class PersonSerializer(serializers.ModelSerializer):
employee_code = serializers.SlugRelatedField(
source='person_info',
slug_field='code',
read_only=True,
)
class Meta:
model = Person
fields = ('name', 'address', 'employee_code')
Or, if you don't want to change the ForeignKey, you could add a employee_code property method to the model instead to return the first employee code in the person_info relation.
class Person(models.Model):
name = models.CharField(max_length=100)
address = models.CharField(max_length=100)
#property
def employee_code(self):
employees = self.person_info.filter()
if employees.exists():
return employees.first().code
return ''
class Employee(models.Model):
person = models.OneToOneField(Person, related_name='person_info')
code = models.CharField()
class PersonSerializer(serializers.ModelSerializer):
employee_code = serializers.CharField(
read_only=True,
)
class Meta:
model = Person
fields = ('name', 'address', 'employee_code')

you can access the reverse relation with custom SerializerMethodField()
class PersonSerializer(serializers.ModelSerializer):
employee_code = serializers.SerializerMethodField()
def get_employee_code(self, obj):
return obj.person_info.code
class Meta:
model = Person
fields = ('name', 'address', 'employee_code')

django rest serialize level 2 field

Hi I need to add a field in a serializer of a 2 level reference item.
I have the following model:
model.py:
class Company(models.Model):
companyName = models.CharField(max_length=50, blank=True)
class Poll(models.Model):
questionString = models.CharField(max_length=500, blank=True)
companyId = models.ForeignKey(Company, null=True, db_column='companyId', blank=True)
class PossibleAnswer(models.Model):
answerString = models.CharField(max_length=100, blank=True)
pollId = models.ForeignKey(Poll, null=True, db_column='pollId', blank=True,related_name='answers')
token = models.CharField(max_length=10, blank=True)
serializers.py:
class PossibleAnswerSerializer(serializers.ModelSerializer):
#companyId = serializers.RelatedField()
class Meta:
model = PossibleAnswer
fields = ('answerString', 'token', 'pollId', 'companyId')
I want to make a Serializer for the PossibleAnswer object that has a field named company. How to make a this reference? Something similar to: pollId__companyId in a django query set filter.

Another solution...
class PossibleAnswerSerializer(serializers.ModelSerializer):
companyId = serializers.SerializerMethodField()
def get_companyId(self, obj):
return obj.pollId.companyId
class Meta:
model = PossibleAnswer
fields = ('answerString', 'token', 'pollId', 'companyId',)

I the field is read-only you can easily achieve this with a serializers.Field, which accept dotted paths to the source.
Your Serializer would be:
class PossibleAnswerSerializer(serializers.ModelSerializer):
companyId = serializers.Field(source='pollId.companyId')
class Meta:
model = PossibleAnswer
fields = ('answerString', 'token', 'pollId', 'companyId')
I too agree with Erik, that naming model attributes with Id is a bad idea even though the DB representation is only the ID.