I want to keep the latest record of a user:
class Record(models.Model):
name = models.ForeignKey(User, on_delete=models.CASCADE)
image = models.ImageField(default='default.jpg', upload_to='site_pics')
date = models.DateTimeField(null=True, blank=True, auto_now_add=True)
def save(self, *args, **kwargs):
super(Record, self).save(*args, **kwargs)
numdata = Record.objects.select_related('name').count()
print(numdata)
#if numdata > 1:
# Record.objects.select_related('name').first().delete()
As per this post Filter latest record in Django, I tried:
.distinct()
.select_related()
.prefetch_related()
None of them return the correct number of records or don't work at all because I'm using SQLite.
Thank you for any suggestions
In that case it might be better to change the modeling to a OneToOneField, such that the database will reject a second Record for the same user. You might also want to change the name of the relation to user, since you are referring to a user object, not its name.
In the save(…) method, you can look if the primary key is not yet filled in, if that is the case, you can delete the original record of the user. Regardless whether that exists or not. If this records does not exist, then it will act as no-op, where nothing changes in the database:
class Record(models.Model):
user = models.OneToOneField(User, on_delete=models.CASCADE)
image = models.ImageField(default='default.jpg', upload_to='site_pics')
date = models.DateTimeField(null=True, blank=True, auto_now_add=True)
def save(self, *args, force_insert=False, **kwargs):
if self.pk is None or force_insert:
Record.objects.filter(user_id=self.user_id).delete()
return super().save(*args, force_insert=force_insert, **kwargs)
Note: It is normally better to make use of the settings.AUTH_USER_MODEL [Django-doc] to refer to the user model, than to use the User model [Django-doc] directly. For more information you can see the referencing the User model section of the documentation.
Related
I'm new to Python and Django and there are some things I would like to achieve in models.py:
After a user submits a form I would like to safe both the current date and the current user_id of the user into the database.
I know django offers to use #property decorators for those, but the problem with that is that I would like to make SQL queries using user_id and that doesn't work with decorators.
Another related question is how to establish calc fields like an automatic calculation of two values in the form before submitting.
Try making a model for the submission of the form. And give the model a foreign key which is connected to the user. Then add a DateField and prove the default value as datetime.now() from the datetime module which is probably already installed on your device.
In settings.py I added this line: 'crum.CurrentRequestUserMiddleware',
In models.py:
from django.contrib.auth.models import User
import crum
class PlantSpecies(models.Model):
def save(self, *args, **kwargs):
userid = crum.get_current_user()
self.userid = userid.id
super(PlantSpecies, self).save(*args, **kwargs)
userid = models.CharField(max_length=45, blank=True, default=crum.get_current_user())
date = models.DateTimeField(auto_now_add=True)
species = models.CharField(max_length=45, blank=True)
common_name = models.CharField(max_length=30, null=True, blank=True)
def __str__(self):
return self.species
I have an API which I pass some sample data. I am overwriting the post method by copying the Queryset so I can manipulate the output data. I would like to access the value of a foreign key relationship but I can only access the foreign key itself.
Like so:
def post(self, request, *args, **kwargs):
data_request = request.data
data_request = data_request.copy()
machine_na = data_request.__getitem__('project')
##this gives me the id of the foreign key
data_request.__setitem__('project', str('my value'))
return Response(data_request, *args, **kwargs)
Now that works. But I can't access the name of the foreign key.
My models as Foreign Keys:
class Machine(models.Model):
machine_name = models.CharField(max_length=120, primary_key=True)
def __str__(self):
return self.machine_name
class Project(models.Model):
project_name = models.CharField(max_length=120, primary_key=True)
def __str__(self):
return self.project_name
My model that refers to the others:
class Simulation(models.Model):
user = models.ForeignKey(settings.AUTH_USER_MODEL, on_delete=models.CASCADE, default=1)
machine = models.ForeignKey(Machine, on_delete=models.CASCADE, default=1)
project
I hope I am clear enough. I would like to access the specific name of, for example, foreign key 2.
calling 'project.project_name' doesn't work and everything else I tried also not.
Any help is highly appreciated. Thanks in advance
Get the project object using the key and then get the name from the object.
project=Project.objects.get(id=int(self.request.POST['project']))
machine_na = project.project_name
So I'm still new to Django. I have a single field in my form. And I was just wondering whether or not I need a form save function or a model save function? When is it appropriate to use either or?
For instance: My form:
class OpinionStatusForm(forms.Form):
choices = (('0', "Your Status"), ('1', "This"), ('2', "That"), ('3', "The Other"))
status = forms.CharField(max_length=2, widget=forms.Select(choices=choices, attrs={'class':'status_dropdown','onchange': 'this.form.submit();'}), required=False)
def save(self, opinion_status):
opinion_status.status = self.cleaned_data['status']
My model:
class OptionStatus(models.Model):
user = models.ForeignKey(User, null=True, unique=True)
status = models.CharField(max_length=2, choices=opinion_statuses)
opinion = models.ForeignKey(Opinion, null=True, blank=True)
def __unicode__(self):
return self.status
def save(self, *args, **kwargs):
super(OpinionStatus, self).save(*args, **kwargs)
I'm going to be ajax-ing the form. I don't know if that makes a difference or not. Thanks!
What you actually need, is a ModelForm. In your example you're working with a standard forms.Form. This is not bound to a model instance. As a result, there's also no need for a save method. The best examples are really given inside the Django docs:
https://docs.djangoproject.com/en/dev/topics/forms/modelforms/
Go step by step over the code examples and you'll understand. It would be too much to explain it all in one Stackoverflow answer - and the Django docs are incredible thorough.
class Product(models.Model):
title = models.CharField(max_length=75)
class Deal(models.Model):
product = models.ForeignKey(Product)
slug = models.SlugField(max_length=255, unique=True)
Having a similar basic setup as above, I want to generate unique slugs for each Deal instance using product title of it's deal and id of the deal itself. IE: "apple-iphone-4s-161" where 161 is the id of the deal and the text before is the title of the product.
For this, how can I overwrite the save() method of the Deal model to apply it?
Of course you can simply overwrite save() method on model (or make receiver for post_save signal).
It will be something like:
from django.template.defaultfilters import slugify
class Deal(models.Model):
product = models.ForeignKey(Product)
slug = models.SlugField(max_length=255, unique=True)
def save(self, *args, **kwargs):
super(Deal, self).save(*args, **kwargs)
if not self.slug:
self.slug = slugify(self.product.title) + "-" + str(self.id)
self.save()
But what is ugly in this solution is that it will hit database twice (it is saved two times). It is because when creating new Deal object it will not have id until you save it for the first time (and you cannot do much about it).
i've bumped at this problem and tested the jasisz solution, and got the max recursion depth exceeded error, so i've fiddle it little and this is how looks for me:
def save(self, *args, **kwargs):
if not self.id:
self.slug = slugify(self.title)
super(Node, self).save(*args, **kwargs)
You could edit this to suit your needs, it tests if this records exists, if not then it creates the slug field otherwise is update and no need for modifieng the slug field.
hope it helps.
You should not have your id in that slug field at all. The two main reasons for this are:
It creates the problem you are having
It's redundant data in the database – the id is already stored
But there is a simple solution to your problem: The only reason why the slug is stored in the database is so you can find a row by slug. But you don't need that – you have the ID. So you should do this:
class DealManager(models.Manager):
def get_by_slug(slug):
return self.get(id=slug.rsplit('-', 1)[1])
class Deal(models.Model):
product = models.ForeignKey(Product)
objects = DealManager()
#property
def slug(self):
return slugify(f'{self.name}-f{self.id}')
In your view or wherever you need to retrieve an item given a slug, you can just do Deal.objects.get_by_slug(slug).
I know this may not exactly work for your situation, but I remember bumping into a similar case. I think I had a created_at field in my model that has auto_now=True. Or something simillar
My slug would look like like this
self.slug = '%s-%s' %(
slugify(self.title),
self.created_at
)
or you can have
self.slug = '%s-%s' %(
slugify(self.title),
datetime.datetime.now()
)
just make sure that the slug max_length is long enough to include the full created_at time, as well as the title, so that you don't end up with non-unique or over max length exceptions.
I'm trying to create a transaction history for each transaction on a Django based marketplace.
I thought the best way of keeping track of this data was to override the save() function and create a Transaction record.
class Transaction(models.Model):
item = models.ManyToManyField(Item, blank=True)
buyer = models.ManyToManyField(User, related_name='buyer')
seller = models.ManyToManyField(User, related_name='seller')
description = models.CharField(max_length=500)
purchase_date = models.DateField(auto_now_add=True)
value = models.DecimalField(max_digits=7, decimal_places=2)
def save(self, *args, **kwargs):
self.buyer.money+=self.value
self.seller.money-=self.value
super(Transaction, self).save(*args, **kwargs)
Am I going about this all wrong? Currenlty I get...
'Transaction' instance needs to have a primary key value before a many-to-many relationship can be used.
You have to save your object before you can go through many-to-many relationships.
Please explain how you can have multiple buyers and sellers on a single transaction. (For the rest of this answer, I'm assuming that there aren't and you meant for these to be ForeignKey fields.)
The related names for buyer and seller are not clear. See below.
I'm not sure what description is for. Is it different from the item list?
item should be called items, since it can be plural, and you might want to create a custom junction table (using the "through" parameter) with a quantity field.
You forgot to save the related objects.
Modified version:
class Transaction(models.Model):
items = models.ManyToManyField(Item, through='TransactionItem', blank=True)
buyer = models.ForeignKey(User, related_name='transactions_as_buyer')
seller = models.ForeignKey(User, related_name='transactions_as_seller')
description = models.CharField(max_length=500)
purchase_date = models.DateField(auto_now_add=True)
value = models.DecimalField(max_digits=7, decimal_places=2)
def save(self, *args, **kwargs):
super(Transaction, self).save(*args, **kwargs)
self.buyer.money += self.value
self.buyer.save()
self.seller.money -= self.value
self.seller.save()
class TransactionItem(models.Model):
transaction = models.ForeignKey(Transaction)
item = models.ForeignKey(Item)
quantity = models.IntegerField()
The buyer and seller fields are many to many fields so self.buyer will never work, I think you were meaning to use ForeignKey instead of ManyToManyField.