Develop Reference

Serializer validate function is not called DRF

class ChildSerializer(serializers.ModelSerializer):
class Meta:
model = Child
fields = '__all__'
class ParentSerializer(serializers.ModelSerializer):
"""
Serializer for task
"""
def validate_title(self, data):
if not data.get('title'):
raise serializers.ValidationError('Please set title')
return data
Validate Function is not called when Post ,Also how can i give custom errors to ChildSerializer ,

I ran into a similar problem where my custom validation field was not being called. I was writing it to bypass an incorrect DRF validation (more details shown below, but not necessary for the answer).
Looking into the DRF source code I found my problem: DRF always validates your field using its code before validating with your custom code.
''' rest-framework/serializers.py '''
for field in fields:
validate_method = getattr(self, 'validate_' + field.field_name, None)
primitive_value = field.get_value(data)
try:
# DRF validation always runs first!
# If DRF validator throws, then custom validation is not called
validated_value = field.run_validation(primitive_value)
if validate_method is not None:
# this is your custom validation
validated_value = validate_method(validated_value)
except ValidationError as exc:
errors[field.field_name] = exc.detail
except DjangoValidationError as exc:
errors[field.field_name] = get_error_detail(exc)
Answer: Custom validators cannot be used to bypass DRF's validators, as they will always run first and will raise an exception before you can say it is valid.
(for those interested, the validation error I hit was like this: ModelSerializer used for ModelA, which has a OneToOne relation to ModelB. ModelB has a UUID for its pk. DRF throws the error '53abb068-0286-411e-8729-0174635c5d81' is not a valid UUID. when validating, which is incorrect, and really infuriating.)

Your ParentSerializer validation method has some issues. Assumes that there is a title field in your ParentSerializer model. For field level validation, you will get the field instead of whole data. That is validate_title function should have title(title field of the data) as parameter not data. So you dont have to check data.get('title') for the existance of title. Reference
class ParentSerializer(serializers.ModelSerializer):
"""
Serializer for task
"""
def validate_title(self, title):
if not title:
raise serializers.ValidationError('Please set title')
return title

In addition to #sean.hudson's answer I was trying to figure out how to override the child serializer validation.
It might be possible to "skip" or more accurately ignore children serializer validation errors, by overriding to_internal_value of the ParentSerialzer:
class ParentSerializer(serializers.ModelSerializer):
children = ChildSerializer(many=True)
def to_internal_value(self, *args, **kwargs):
try:
# runs the child serializers
return super().to_internal_value(*args, **kwargs)
except ValidationError as e:
# fails, and then overrides the child errors with the parent error
return self.validate(self.initial_data)
def validate(self, attrs):
errors = {}
errors['custom_override_error'] = 'this ignores and overrides the children serializer errors'
if len(errors):
raise ValidationError(errors)
return attrs
class Meta:
model = Parent

My problem was that I had my own custom to_internal_value method. Removing it fixed the issue.
class EventSerializer(serializers.Serializer):
end_date = serializers.DateTimeField(format=DATE_FORMAT, required=True)
start_date = serializers.DateTimeField(format=DATE_FORMAT, required=True)
description = serializers.CharField(required=True)
def validate_start_date(self, start_date):
return start_date
def validate_end_date(self, end_date):
return end_date
# def to_internal_value(self, data):
# if data.get('start_date', False):
# data['start_date'] = datetime.strptime(data['start_date'], DATE_FORMAT)
# if data.get('end_date', False):
# data['end_date'] = datetime.strptime(data['end_date'], DATE_FORMAT)
# return data

I would like to add what the official documentation says, I hope it can be of help.
Field-level validation
You can specify custom field-level validation by adding .validate_<field_name> methods to your Serializer subclass. These are similar to the .clean_<field_name> methods on Django forms.
These methods take a single argument, which is the field value that requires validation.
Your validate_<field_name> methods should return the validated value or raise a serializers.ValidationError. For example:
from rest_framework import serializers
class BlogPostSerializer(serializers.Serializer):
title = serializers.CharField(max_length=100)
content = serializers.CharField()
def validate_title(self, value):
"""
Check that the blog post is about Django.
"""
if 'django' not in value.lower():
raise serializers.ValidationError("Blog post is not about Django")
return value`

Django Rest Framework partial update

I'm trying to implement partial_update with Django Rest Framework but I need some clarification because I'm stuck.
Why do we need to specify partial=True?
In my understanding, we could easily update Demo object inside of partial_update method. What is the purpose of this?
What is inside of serialized variable?
What is inside of serialized variable in partial_update method? Is that a Demo object? What function is called behind the scenes?
How would one finish the implementation here?
Viewset
class DemoViewSet(viewsets.ModelViewSet):
serializer_class = DemoSerializer
def partial_update(self, request, pk=None):
serialized = DemoSerializer(request.user, data=request.data, partial=True)
return Response(status=status.HTTP_202_ACCEPTED)
Serializer
class DemoSerializer(serializers.ModelSerializer):
class Meta:
model = Demo
fields = '__all__'
def update(self, instance, validated_data):
print 'this - here'
demo = Demo.objects.get(pk=instance.id)
Demo.objects.filter(pk=instance.id)\
.update(**validated_data)
return demo

I when digging into the source code of rest_framework and got the following findings:
For question 1. Why do we need to specify partial=True?
This question is related to HTTP verbs.
PUT: The PUT method replaces all current representations of the target resource with the request payload.
PATCH: The PATCH method is used to apply partial modifications to a resource.
Generally speaking, partial is used to check whether the fields in the model is needed to do field validation when client submitting data to the view.
For example, we have a Book model like this, pls note both of the name and author_name fields are mandatory (not null & not blank).
class Book(models.Model):
name = models.CharField('name of the book', max_length=100)
author_name = models.CharField('the name of the author', max_length=50)
# Create a new instance for testing
Book.objects.create(name='Python in a nut shell', author_name='Alex Martelli')
For some scenarios, we may only need to update part of the fields in the model, e.g., we only need to update name field in the Book. So for this case, client will only submit the name field with new value to the view. The data submit from the client may look like this:
{"pk": 1, name: "PYTHON IN A NUT SHELL"}
But you may have notice that our model definition does not allow author_name to be blank. So we have to use partial_update instead of update. So the rest framework will not perform field validation check for the fields which is missing in the request data.
For testing purpose, you can create two views for both update and partial_update, and you will get more understanding what I just said.
Example:
views.py
from rest_framework.generics import GenericAPIView
from rest_framework.mixins import UpdateModelMixin
from rest_framework.viewsets import ModelViewSet
from rest_framework import serializers
class BookSerializer(serializers.ModelSerializer):
class Meta:
model = Book
class BookUpdateView(GenericAPIView, UpdateModelMixin):
'''
Book update API, need to submit both `name` and `author_name` fields
At the same time, or django will prevent to do update for field missing
'''
queryset = Book.objects.all()
serializer_class = BookSerializer
def put(self, request, *args, **kwargs):
return self.update(request, *args, **kwargs)
class BookPartialUpdateView(GenericAPIView, UpdateModelMixin):
'''
You just need to provide the field which is to be modified.
'''
queryset = Book.objects.all()
serializer_class = BookSerializer
def put(self, request, *args, **kwargs):
return self.partial_update(request, *args, **kwargs)
urls.py
urlpatterns = patterns('',
url(r'^book/update/(?P<pk>\d+)/$', BookUpdateView.as_view(), name='book_update'),
url(r'^book/update-partial/(?P<pk>\d+)/$', BookPartialUpdateView.as_view(), name='book_partial_update'),
)
Data to submit
{"pk": 1, name: "PYTHON IN A NUT SHELL"}
When you submit the above json to the /book/update/1/, you will got the following error with HTTP_STATUS_CODE=400:
{
"author_name": [
"This field is required."
]
}
But when you submit the above json to /book/update-partial/1/, you will got HTTP_STATUS_CODE=200 with following response,
{
"id": 1,
"name": "PYTHON IN A NUT SHELL",
"author_name": "Alex Martelli"
}
For question 2. What is inside of serialized variable?
serialized is a object wrapping the model instance as a serialisable object. and you can use this serialized to generate a plain JSON string with serialized.data .
For question 3. How would one finish the implementation here?
I think you can answer yourself when you have read the answer above, and you should have known when to use update and when to used partial_update.
If you still have any question, feel free to ask. I just read part of the source code of the rest framework, and may have not understand very deeply for some terms, and please point it out when it is wrong...

For partial update - PATCH http method
For full update - PUT http method
When doing an update with DRF, you are supposed to send request data that includes values for all (required) fields. This is at least the case when the request is via the PUT http method. From what I understand, you want to update one or at least not all model instance fields. In this case make a request with the PATCH http method. Django rest framework (DRF) will take care of it out of the box.
Example (with token auth):
curl -i -X PATCH -d '{"name":"my favorite banana"}' -H "Content-Type: application/json" -H 'Authorization: Token <some token>' http://localhost:8000/bananas/

So simple, just override init method of your serializer like that:
def __init__(self, *args, **kwargs):
kwargs['partial'] = True
super(DemoSerializer, self).__init__(*args, **kwargs)

Just a quick note as it seems that nobody has already pointed this out:
serialized = DemoSerializer(request.user, data=request.data, partial=True)
The first argument of DemoSerializer should be a Demo instance, not a user (at least if you use DRF 3.6.2 like me).
I don't know what you are trying to do, but this is a working example:
def partial_update(self, request, *args, **kwargs):
response_with_updated_instance = super(DemoViewSet, self).partial_update(request, *args, **kwargs)
Demo.objects.my_func(request.user, self.get_object())
return response_with_updated_instance
I do the partial update and then I do other things calling my_func and passing the current user and the demo instance already updated.
Hope this helps.

I had an issue where my multi-attribute/field validation in a rest_framework serializer was working with a POST /resources/ request but failing with a PATCH /resources/ request. It failed in the PATCH case because it was only looking for values in the supplied attrs dict and not falling back to values in self.instance. Adding a method get_attr_or_default to do that fallback seems to have worked:
class EmailSerializer(serializers.ModelSerializer):
def get_attr_or_default(self, attr, attrs, default=''):
"""Return the value of key ``attr`` in the dict ``attrs``; if that is
not present, return the value of the attribute ``attr`` in
``self.instance``; otherwise return ``default``.
"""
return attrs.get(attr, getattr(self.instance, attr, ''))
def validate(self, attrs):
"""Ensure that either a) there is a body or b) there is a valid template
reference and template context.
"""
existing_body = self.get_attr_or_default('body', attrs).strip()
if existing_body:
return attrs
template = self.get_attr_or_default('template', attrs)
templatecontext = self.get_attr_or_default('templatecontext', attrs)
if template and templatecontext:
try:
render_template(template.data, templatecontext)
return attrs
except TemplateRendererException as err:
raise serializers.ValidationError(str(err))
raise serializers.ValidationError(NO_BODY_OR_TEMPLATE_ERROR_MSG)

I don't know why, but for me, the only way to solve it was to override the validate method in the Serializer class.
Maybe it's related to the fact that I'm using MongoDB with Djongo
class DemoSerializer(serializers.ModelSerializer):
def validate(self, attrs):
self._kwargs["partial"] = True
return super().validate(attrs)

You forgot serializer.save()
You can finish it the following way . . .
class DemoViewSet(viewsets.ModelViewSet):
serializer_class = DemoSerializer
def partial_update(self, request, pk=None):
serializer = DemoSerializer(request.user, data=request.data, partial=True)
serializer.save()
serializer.is_valid(raise_exception=True)
return Response(serializer.data)
Also, you shouldn't need to override the update method in the serializer.

Multiple Models in Django Rest Framework?

I am using Django Rest framework. I want to serialize multiple models and send them as a response. Currently I can send only one model per view (like CartView below sends only Cart object). Following models (unrelated) can be there.
class Ship_address(models.Model):
...
class Bill_address(models.Model):
...
class Cart(models.Model):
...
class Giftwrap(models.Model):
...
I tried using DjangoRestMultipleModels, it works ok but has some limitations. Is there any in-built way? Can't I append to the serializer that's created in the following view?
from rest_framework.views import APIView
class CartView(APIView):
"""
Returns the Details of the cart
"""
def get(self, request, format=None, **kwargs):
cart = get_cart(request)
serializer = CartSerializer(cart)
# Can't I append anything to serializer class like below ??
# serializer.append(anotherserialzed_object) ??
return Response(serializer.data)
I really like DRF. But this use-case (of sending multiple objects) makes me wonder if writing a plain-old Django view will be better suited for such a requirement.

You can customize it, and it wouldn't be too weird, because this is an APIView (as opposed to a ModelViewSet from which a human being would expect the GET to return a single model) e.g. you can return several objects from different models in your GET response
def get(self, request, format=None, **kwargs):
cart = get_cart(request)
cart_serializer = CartSerializer(cart)
another_serializer = AnotherSerializer(another_object)
return Response({
'cart': cart_serializer.data,
'another': another_serializer.data,
'yet_another_field': 'yet another value',
})

Django : how to Identify who is saving the model from program?

How do I check from the django code, which User is saving a model currently ?
I need to throw Validation Errors or assign some permissions to him from that.

Assuming you execute the model.save() from a view function, you can get the current user with request.user.
from django.contrib.auth.models import Permission
def myview(request):
model = Model(...)
model.save()
permission = Permission.objects.get(codename="...")
request.user.user_permissions.add(permission)
EDIT: Access the request in a form
The simplest way to get at the request from your form validation code is probably to set a attribute on the form instance:
def myview(request):
...
form = SomeForm(...)
form.request = request
Inside your form validation logic you can now use self.request to access the user:
class SomeForm(...):
def clean_somefield(self):
data = self.cleaned_data["somefield"]
if self.request.user....:
raise ValidationError()

Django Admin - how to prevent deletion of some of the inlines

I have 2 models - for example, Book and Page.
Page has a foreign key to Book.
Each page can be marked as "was_read" (boolean), and I want to prevent deleting pages that were read (in the admin).
In the admin - Page is an inline within Book (I don't want Page to be a standalone model in the admin).
My problem - how can I achieve the behavior that a page that was read won't be deleted?
I'm using Django 1.4 and I tried several options:
Override "delete" to throw a ValidationError - the problem is that the admin doesn't "catch" the ValidationError on delete and you get an error page, so this is not a good option.
Override in the PageAdminInline the method - has_delete_permission - the problem here -it's per type so either I allow to delete all pages or I don't.
Are there any other good options without overriding the html code?
Thanks,
Li

The solution is as follows (no HTML code is required):
In admin file, define the following:
from django.forms.models import BaseInlineFormSet
class PageFormSet(BaseInlineFormSet):
def clean(self):
super(PageFormSet, self).clean()
for form in self.forms:
if not hasattr(form, 'cleaned_data'):
continue
data = form.cleaned_data
curr_instance = form.instance
was_read = curr_instance.was_read
if (data.get('DELETE') and was_read):
raise ValidationError('Error')
class PageInline(admin.TabularInline):
model = Page
formset = PageFormSet

You could disable the delete checkbox UI-wise by creating your own custom
formset for the inline model, and set can_delete to False there. For
example:
from django.forms import models
from django.contrib import admin
class MyInline(models.BaseInlineFormSet):
def __init__(self, *args, **kwargs):
super(MyInline, self).__init__(*args, **kwargs)
self.can_delete = False
class InlineOptions(admin.StackedInline):
model = InlineModel
formset = MyInline
class MainOptions(admin.ModelAdmin):
model = MainModel
inlines = [InlineOptions]

Another technique is to disable the DELETE checkbox.
This solution has the benefit of giving visual feedback to the user because she will see a grayed-out checkbox.
from django.forms.models import BaseInlineFormSet
class MyInlineFormSet(BaseInlineFormSet):
def add_fields(self, form, index):
super().add_fields(form, index)
if some_criteria_to_prevent_deletion:
form.fields['DELETE'].disabled = True
This code leverages the Field.disabled property added in Django 1.9. As the documentation says, "even if a user tampers with the field’s value submitted to the server, it will be ignored in favor of the value from the form’s initial data," so you don't need to add more code to prevent deletion.

In your inline, you can add the flag can_delete=False
EG:
class MyInline(admin.TabularInline):
model = models.mymodel
can_delete = False

I found a very easy solution to quietly avoid unwanted deletion of some inlines. You can just override delete_forms property method.
This works not just on admin, but on regular inlines too.
from django.forms.models import BaseInlineFormSet
class MyInlineFormSet(BaseInlineFormSet):
#property
def deleted_forms(self):
deleted_forms = super(MyInlineFormSet, self).deleted_forms
for i, form in enumerate(deleted_forms):
# Use form.instance to access object instance if needed
if some_criteria_to_prevent_deletion:
deleted_forms.pop(i)
return deleted_forms