In Django, is there a way to create a object, create its related objects, then save them all at once?
For example, in the code below:
from django.db import models
class Post(models.Model):
title = models.CharField(max_length=255)
body = models.CharField(max_length=255)
class Tag(models.Model):
post = models.ForeignKey(Post)
title = models.CharField(max_length=255)
post = Post(title='My Title', body='My Body')
post.tag_set = [Tag(post=post, title='test tag'), Tag(post=post, title='second test tag')]
post.save()
I create a Post object. I then also want to create and associate my Tag objects. I want to avoid saving the Post then saving the Tags because if a post.save() succeeds, then a tag.save() fails, I'm left with a Post with no Tags.
Is there a way in Django to save these all at once or at least enforce better data integrity?
transactions to the rescue !
from django.db import transaction
with transaction.atomic():
post = Post.objects.create('My Title', 'My Body')
post.tag_set = [Tag(post, 'test tag'), Tag(post, 'second test tag')]
As a side note: I think you really want a many to many relationship between Post and Tag...
override save...
class Post(models.Model):
...
def save(self, *args, **kwargs):
super(Post, self).save(*args, **kwargs)
for tag in self.tag_set:
tag.save()
This way you don't have to write the transaction thing over and over again. If you want to use transactions, just implement it in the save method instead of doing the loop.
Related
SOLUTION AT THE BOTTOM
Problem: Django form populating with list of objects rather than values
Summary: I have 2 models Entities and Breaks. Breaks has a FK relationship to the entity_id (not the PK) on the Entities model.
I want to generate an empty form for all the fields of Breaks. Generating a basic form populates all the empty fields, but for the FK it generates a dropdown list of all objects of the Entities table. This is not helpful so I have excluded this in the ModelForm below and tried to replace with a list of all the entity_ids of the Entities table. This form renders as expected.
class BreakForm(ModelForm):
class Meta:
model = Breaks
#fields = '__all__'
exclude = ('entity',)
def __init__(self, *args, **kwargs):
super(BreakForm, self).__init__(*args, **kwargs)
self.fields['entity_id'] = ModelChoiceField(queryset=Entities.objects.all().values_list('entity_id', flat=True))
The below FormView is the cbv called by the URL. As the below stands if I populate the form, and for the FK column entity_id choose one of the values, the form will not submit. By that field on the form template the following message appears Select a valid choice. That choice is not one of the available choices.
class ContactFormView(FormView):
template_name = "breaks/test/breaks_form.html"
form_class = BreakForm
My initial thoughts were either that the datatype of this field (string/integer) was wrong or that Django needed the PK of the row in the Entities table (for whatever reason).
So I added a post function to the FormView and could see that the request.body was populating correctly. However I can't work out how to populate this into the ModelForm and save to the database, or overcome the issue mentioned above.
Addendum:
Models added below:
class Entity(models.Model):
pk_securities = models.AutoField(primary_key=True)
entity_id = models.CharField(unique=True)
entity_description = models.CharField(blank=True, null=True)
class Meta:
managed = False
db_table = 'entities'
class Breaks(models.Model):
pk_break = models.AutoField(primary_key=True)
date = models.DateField(blank=True, null=True)
entity = models.ForeignKey(Entity, on_delete= models.CASCADE, to_field='entity_id')
commentary = models.CharField(blank=True, null=True)
active = models.BooleanField()
def get_absolute_url(self):
return reverse(
"item-update", args=[str(self.pk_break)]
)
def __str__(self):
return f"{self.pk_break}"
class Meta:
managed = False
db_table = 'breaks'
SOLUTION
Firstly I got this working by adding the following to the Entity Model class. However I didn't like this as it would have consequences elsewhere.
def __str__(self):
return f"{self.entity_id}"
I found this SO thread on the topic. The accepted answer is fantastic and the comments to it are helpful.
The solution is to subclass ModelChoiceField and override the label_from_instance
class EntityChoiceField(ModelChoiceField):
def label_from_instance(self, obj):
return obj.entity_id
I think your problem is two fold, first is not rendering the dropdown correctly and second is form is not saving. For first problem, you do not need to do any changes in ModelChoiceField queryset, instead, add to_field_name:
class BreakForm(ModelForm):
class Meta:
model = Breaks
#fields = '__all__'
def __init__(self, *args, **kwargs):
super(BreakForm, self).__init__(*args, **kwargs)
self.fields['entity_id'] = ModelChoiceField(queryset=Entities.objects.all(), to_field_name='entity_id')
Secondly, if you want to save the form, instead of FormView, use CreateView:
class ContactFormView(CreateView):
template_name = "breaks/test/breaks_form.html"
form_class = BreakForm
model = Breaks
In Django, the request object passed as parameter to your view has an attribute called "method" where the type of the request is set, and all data passed via POST can be accessed via the request. POST dictionary. The view will display the result of the login form posted through the loggedin. html.
I've been scratching my head about this problem for a couple of hours now. Basically, I have two models: User and Project:
class User(AbstractUser):
username = None
email = models.EmailField("Email Address", unique=True)
avatar = models.ImageField(upload_to="avatars", default="avatars/no_avatar.png")
first_name = models.CharField("First name", max_length=50)
last_name = models.CharField("Last name", max_length=50)
objects = UserManager()
USERNAME_FIELD = "email"
class Project(models.Model):
name = models.CharField("Name", max_length=8, unique=True)
status = models.CharField(
"Status",
max_length=1,
choices=[("O", "Open"), ("C", "Closed")],
default="O",
)
description = models.CharField("Description", max_length=3000, default="")
owner = models.ForeignKey(
User, on_delete=models.SET_NULL, null=True, related_name="project_owner"
)
participants = models.ManyToManyField(User, related_name="project_participants", blank=True)
created_at = models.DateTimeField(auto_now_add=True)
I use standard ModelViewSets for both of them, nothing changed. Then there's my Project serializer:
class ProjectSerializer(serializers.ModelSerializer):
class Meta:
model = Project
fields = "__all__"
status = serializers.CharField(source="get_status_display", required=False)
owner = UserSerializer()
participants = UserSerializer(many=True)
I use UserSerializers here, because having them achieved first of my two goals:
I wanted to get the user data when getting the project from the API -> owner is a serialized User with all the fields, same for participants, but it's a list of users
I want to be able to partially update the Project, for example add a participant
So I searched through the docs and SO and I always found answers that answer one of those questions, but never both of them.
The thing with my second goal is: when I do the partial update (via PATCH, of course), I get the response that: "Invalid data. Expected a dictionary, but got int." when I pass a list of ints (user ids) for the participants. I thought: okay, maybe I have to pass the whole user data to change it. But then I realised: when I remove the UserSerializer from ProjectSerializer - passing just the list of ints in Postman works just fine. And that is a life saver, cuz who wants to create a request with a whole bunch of data, when I can just pass user ids.
But then of course when I remove the UserSerializer, when I call get project, I get participants: [1,2,3,4,...], not participants: [{"id": 1, "name": "John", ...}, ...}]. And I really want this behavior, because I don't want to make additional API calls just to get the users' data by their IDs.
So summing up my question is: Is there a way to leave those serializers in place but still be able to partially update my model without having to pass whole serialized data to the API (dicts instead of IDs)? Frankly, I don't care about the serializers, so maybe the question is this: Can I somehow make it possible to partially update my Products' related fields like owner or participants just by passing the related entities IDs while still maintaining an ability to get my projects with those fields expanded (serialized entities - dicts, instead of just IDs)?
#Edit:
My view:
from rest_framework import viewsets, permissions
from projects.models import Project
from projects.api.serializers import ProjectSerializer
class ProjectViewSet(viewsets.ModelViewSet):
queryset = Project.objects.all()
serializer_class = ProjectSerializer
permission_classes = [permissions.IsAuthenticated]
lookup_field = "name"
def get_queryset(self):
if self.request.user.is_superuser:
return Project.objects.all()
else:
return Project.objects.filter(owner=self.request.user.id)
def perform_create(self, serializer):
serializer.save(owner=self.request.user, participants=[self.request.user])
Answer:
To anyone reading this, I've solved this problem and I actually created a base class for all my viewsets that I want this behavior to be in:
from rest_framework.response import Response
class ReadWriteViewset:
write_serializer_class = None
read_serializer_class = None
def update(self, request, *args, **kwargs):
partial = kwargs.pop("partial", False)
instance = self.get_object()
write_serializer = self.write_serializer_class(
instance=instance,
data=request.data,
partial=partial,
)
write_serializer.is_valid(raise_exception=True)
self.perform_update(write_serializer)
read_serializer = self.read_serializer_class(instance)
if getattr(instance, "_prefetched_objects_cache", None):
# If 'prefetch_related' has been applied to a queryset, we need to
# forcibly invalidate the prefetch cache on the instance.
instance._prefetched_objects_cache = {}
return Response(read_serializer.data)
Then you use it kinda like in here
I'm assuming that you are using a ModelViewSet. You could use different serializers for different methods.
class ProjectViewSet(viewsets.ModelViewSet):
def get_serializer_class(self):
if self.action in ['create', 'update']:
return WriteProjectSerializer # your serializer not using `UserSerializer` that works for updating
return ProjectSerializer # your default serializer with all data
Edit for using different serializers in same method:
# you can override `update` and use a different serializer in the response. The rest of the code is basically the default behavior
def update(self, request, *args, **kwargs):
partial = kwargs.pop('partial', False)
instance = self.get_object()
write_serializer = WriteProjectSerializer(data=request.data)
serializer.is_valid(raise_exception=True)
instance = self.perform_update(serializer)
read_serializer = ProjectSerializer(instance)
if getattr(instance, '_prefetched_objects_cache', None):
# If 'prefetch_related' has been applied to a queryset, we need to
# forcibly invalidate the prefetch cache on the instance.
instance._prefetched_objects_cache = {}
return Response(read_serializer.data)
A good way to see the default code for all these methods is using Classy DRF. You can see all methods that come with using ModelViewSet and use that code with some changes. Here I'm using the default code for update but changing for a new serializer for the response.
Supposing some standard Django relational setup like this:
models.py
class Book(models.Model):
title = models.CharField(max_length=30)
class Page(models.Model):
book = models.ForeignKey(Book, on_delete=models.CASCADE)
text = models.CharField(max_length=100)
I'd like to create a book and all its pages with one request. If we start with serializers like this:
serializers.py
class PageSerializer(serializers.ModelSerializer):
class Meta:
model = Page
fields = '__all__'
class BookSerializer(serializers.ModelSerializer):
class Meta:
model = Book
fields = ('title', 'pages')
pages = PageSerializer(many=True)
Then the problem is that the PageSerializer now requires a book foreign key. But I don't know the key of the book until I've created the book, which is only after I've sent the POST request. So I cannot include the book pk in the POST data that the client sends.
An obvious solution is to override the create function on the Book serializer. But then I am still faced with the problem that the validators will say that the book field is required and the POST data will fail to validate.
I could make book a not-required field on the PageSerialzer. But this seems very bad. The book field IS required. And the BookSerializer create method will be able to supply it. It's just the client that doesn't know it.
So my suspicion is that the best way to do this is to leave book as required on the PageSerializer, but somehow make it so that the validators on the BookSerializer don't check for whether that is in the POST data when I post to BookSerializer.
Is this the correct way to achieve what I want? And if so, how do I do it? Thank you.
Why not try handling it in the create viewset. You can validate the data for the Book object first, before creating it. Then validate the data for the Page object using the created Book object and the other data sent from the request to the page.
I'd link your ViewSet to a BookCreateSerializer, and from this specific serializer I'd then add a function to not only verify the received data but make sure you link the parent's id to the child's one during creation.
IMPORTANT NOTE
This works if a parent only has one child, not sure about when passing multiple children.
Here is what is could look like.
BookCreateSerializer:
class BookCreateSerializer(serializers.ModelSerializer):
"""
Serializer to create a new Book model in DB
"""
pages = PageCreateSerializer()
class Meta:
model = Book
fields = [
'title',
'pages'
]
def create(self, validated_data):
page_data = validated_data.pop('page')
book = Book.objects.create(**validated_data)
Page.objects.create(book=book, **page_data)
return book
PageCreateSerializer
class PageCreateSerializer(serializers.ModelSerializer):
"""
Serializer to create a new Page model in DB
"""
class Meta:
model = Page
fields = [
'book',
'text'
]
To make sure that your Book instance understands what a page field is in the serializer, you have to define a related_name in its child's Model (Page). The name you choose is up to you. It could look like:
class Page(models.Model):
book = models.ForeignKey(Book, on_delete=models.CASCADE, related_name='page')
text = models.CharField(max_length=100)
I have two models:
class Author(models.Model):
name = models.CharField(max_length=100)
create_report = models.BooleanField(default=False)
class Book(models.Model):
author = models.ForeignKey(Author, on_delete=models.PROTECT)
title = models.CharField(max_length=100)
They are registered in admin like this:
class BookInline(admin.TabularInline):
model = PurchaseOrderItem
#admin.register(PurchaseOrder)
class AuthorAdmin(admin.ModelAdmin):
inlines = (PurchaseOrderInline,)
I create an author and two books through Django admin. After I hit the 'Save' button, if Author.create_report == True I would like to see a report saying the following:
Author Whoever-he-is has written the following books:
Title-of-the-first-book
Title-of-the-first-book
(Where the report should appear or how to render the template are not relevant questions here, let's skip them.)
My first idea was to overwrite Author.save() method:
def save(self, *args, **kwargs):
super().save(*args, **kwargs)
if self.create_report:
self.write_report(name=self.name, books=self.book_set.all())
The problem is that Author.save() method is executed before Book objects are saved and so self.book_set.all() is empty.
One workaround would be to use some other ModelAdmin function (for instance log_addition()), which fires after Book objects are saved, but as I wish to use the same functionality out of admin, too, it is not the best solution.
Can I somehow achieve the result without using the admin layer functions?
The book_set.all() will be Null initially, because there is no Book related to the Author at the time of author creation. So, what I'm suggesting is, generate the report whenever a Book is created.
class Author(models.Model):
name = models.CharField(max_length=100)
create_report = models.BooleanField(default=False)
class Book(models.Model):
author = models.ForeignKey(Author, on_delete=models.PROTECT)
title = models.CharField(max_length=100)
def save(self, *args, **kwargs):
pk = self.pk # pk will be None like objects if self is new instance
super().save(*args, **kwargs)
if not pk and self.author.create_report:
write_report(name=self.author.name, books=self.author.book_set.all())
I am having a similar issue. I think this is exactly the reason why Django introduced signals. You can fire and catch a signal of the created Books/Authors and then fire an action from there that creates some sort of report.
But I get your point (since I am feeling the same pain) ... id would be great is this would work straight from the model.
If I have two models in Django application like this:
class Author(models.Model):
name = models.CharField(max_length=100)
class Book(models.Model):
author = models.ForeignKey(Author)
title = models.CharField(max_length=100)
How can I create a single form that allows you add both an Author and a Book simultaneously. If the author exists in the system, I could simply display the book Form and link that to the author but it is very often that I need to allow my users to create the book and the author simultaneously.
How can I do this?
Thanks.
You can write a custom form, which will check if the author exists in the system use existing, if no, create new with provided name.
class CustomForm(forms.ModelForm):
author = forms.CharField()
def save(self, commit=True):
author, created = Author.objects.get_or_create(name=self.cleaned_data['author'])
instance = super(CustomForm,self).save(commit=commit)
instance.author = author
if commit:
instance.save()
return instance
class Meta:
model=Book
Not sure this code is working, but I suppose it can explain my idea.
You can create a view that handles multiple forms - see http://collingrady.wordpress.com/2008/02/18/editing-multiple-objects-in-django-with-newforms/ for an excellent example.
You'd have to ensure that the rendering of the form objects are done in the template with only one tag and one submit button.