All Questions
3,531
questions
111
votes
8
answers
239k
views
How to update() a single model instance retrieved by get() on Django ORM?
I have a function which currently calls Models.object.get(), which returns either 0 or 1 model objects:
if it returns 0, I create a new model instance in the except DoesNotExist clause of the ...
- 6,901
110
votes
4
answers
81k
views
Create if doesn't exist
I have a Django application that reads data from a web API and puts it in a database.
Is there a way to create a new object from a mode but prevent the duplicate exception if the object already exists?...
- 6,690
97
votes
6
answers
187k
views
Check if an object exists
I need to check if Model.objects.filter(...) turned up anything, but do not need to insert anything. My code so far is:
user_pass = log_in(request.POST) # form class
if user_pass.is_valid():
...
- 11.3k
97
votes
1
answer
56k
views
Django's ManyToMany Relationship with Additional Fields
I want to store some additional information in that, automatically created, ManyToMany join-table. How would I do that in Django?
In my case I have two tables: "Employees" and "Projects". What I ...
- 3,026
96
votes
7
answers
103k
views
Raise a validation error in a model's save method in Django
I'm not sure how to properly raise a validation error in a model's save method and send back a clear message to the user.
Basically I want to know how each part of the "if" should end, the one where ...
- 5,715
95
votes
3
answers
19k
views
models.py getting huge, what is the best way to break it up?
Directions from my supervisor:
"I want to avoid putting any logic in the models.py. From here on out, let's use that as only classes for accessing the database, and keep all logic in external classes ...
- 3,144
92
votes
5
answers
86k
views
Django Queryset with filtering on reverse foreign key
I have the following Django model:
class Make:
name = models.CharField(max_length=200)
class MakeContent:
make = models.ForeignKey(Make)
published = models.BooleanField()
I'd like to know ...
- 11.2k
86
votes
8
answers
54k
views
Django get list of models in application
So, i have a file models.py in MyApp folder:
from django.db import models
class Model_One(models.Model):
...
class Model_Two(models.Model):
...
...
It can be about 10-15 classes.
How to find ...
- 3,618
81
votes
2
answers
56k
views
Django - Model graphic representation (ERD) [closed]
I'm searching a way to represent my Django project model graphically.
Is there a "native" way to do this kind of ERD (diagram) ?
Update following @Etienne instructions
Here is an example of ...
- 45.6k
79
votes
6
answers
88k
views
Django required field in model form
I have a form where a couple of fields are coming out as required when I don't want them too. Here is the form from models.py
class CircuitForm(ModelForm):
class Meta:
model = Circuit
...
- 1,095
75
votes
4
answers
85k
views
How can I set two primary key fields for my models in Django?
I have a model like this:
class Hop(models.Model):
migration = models.ForeignKey('Migration')
host = models.ForeignKey(User, related_name='host_set')
How can I have the primary key be the ...
- 5,923
73
votes
11
answers
34k
views
Case insensitive unique model fields in Django?
I have basically a username is unique (case insensitive), but the case matters when displaying as provided by the user.
I have the following requirements:
field is CharField compatible
field is ...
- 1,109
68
votes
5
answers
88k
views
Populating django field with pre_save()?
class TodoList(models.Model):
title = models.CharField(maxlength=100)
slug = models.SlugField(maxlength=100)
def save(self):
self.slug = title
super(TodoList, self).save()
...
- 12.2k
65
votes
3
answers
44k
views
How can I iterate over ManyToManyField?
A simple question and yet I can't find an answer for it.
I have a model with a ManyToMany field:
class Stuff(models.Model):
things = models.ManyToManyField(Thing)
then in a different function I ...
- 10.1k
60
votes
9
answers
35k
views
Can Django automatically create a related one-to-one model?
I have two models in different apps: ModelA and ModelB. They have a one-to-one relationship. Is there a way django can automatically create and save ModelB when ModelA is saved?
class ModelA(models....
- 601
58
votes
1
answer
57k
views
Django model: NULLable field
I'm working on a django project where I need a DateField to sometimes be empty. My model looks like this:
#models.py
end = models.DateField(default=None, blank=True)
But when I run python manage.py ...
- 9,555
57
votes
5
answers
14k
views
Should I avoid multi-table (concrete) inheritance in Django by any means?
Many experienced developers recommend against using Django multi-table inheritance because of its poor performance:
Django gotcha: concrete inheritance by Jacob Kaplan-Moss, a core contributor of ...
- 7,006
54
votes
5
answers
18k
views
How do I get the default value for a field in a Django model?
I have a Django model with some fields that have default values specified. I am looking to grab the default value for one of these fields for us later on in my code. Is there an easy way to grab a ...
- 3,623
50
votes
2
answers
55k
views
optional fields in django models
I have the following model in django.
class Link(models.Model):
name = models.CharField(max_length=100)
url = models.CharField(max_length=100)
tag = models.CharField(max_length=100)
...
- 13.4k
48
votes
2
answers
43k
views
How can I fill up form with model object data?
I want to fill up form with data from model instance. But my form has less fields than model. If I have code like this:
class Item(models.Model)
name = models.CharField(max_length=100)
price =...
- 6,375
47
votes
3
answers
78k
views
ValueError - Cannot assign: must be an instance
I get the following error when I try to run an insert into one of my tables.
Cannot assign "1": "Team.department_id" must be a "Department" instance
Admittedly I'm ...
- 629
46
votes
4
answers
47k
views
Do properties work on Django model fields?
I think the best way to ask this question is with some code... can I do this:
class MyModel(models.Model):
foo = models.CharField(max_length = 20)
bar = models.CharField(max_length = ...
- 75.7k
44
votes
3
answers
50k
views
Django Pass Multiple Models to one Template
I am building an address book that includes the relationships between entries, etc. I have separate models for Individuals, Companies, Venues, and Roles. On my index page I would like to list all of ...
- 1,235
43
votes
3
answers
72k
views
Restrict django FloatField to 2 decimal places
I am looking for a way to limit the FloatField in Django to 2 decimal places. Has anyone got a clue of how this could be done without having to use a DecimalField?
I tried decimal_places=2, but this ...
- 1,012
43
votes
6
answers
75k
views
How can I change a Django form field value before saving?
if request.method == 'POST':
userf = UsersModelForm(request.POST)
username = userf.data['username']
password = userf.data['password']
passwordrepeat = userf.data['passwordrepeat']
...
- 12.3k
43
votes
1
answer
40k
views
AttributeError: 'ManyRelatedManager' object has no attribute 'add'? I do like in django website but got this error
for item in data:
category_id = item['category_id']
del item['category_id']
category = Category.objects.get(pk=category_id)
code = item['code']
try:
article = Article....
- 15.7k
40
votes
3
answers
27k
views
How to get the app a Django model is from?
I have a model with a generic relation:
TrackedItem --- genericrelation ---> any model
I would like to be able to generically get, from the initial model, the tracked item.
I should be able to ...
- 588k
39
votes
5
answers
30k
views
Check if a OneToOne relation exists in Django
Now I'm using django 1.6
I have two models relates with a OneToOneField.
class A(models.Model):
pass
class B(models.Model):
ref_a = models.OneToOneField(related_name='ref_b', null=True)
...
- 18k
36
votes
9
answers
25k
views
Django self-recursive foreignkey filter query for all childs
I have this model with a self referencing Foreign Key relation:
class Person(TimeStampedModel):
name = models.CharField(max_length=32)
parent = models.ForeignKey('self', null=True, blank=True,...
- 11.8k
36
votes
2
answers
17k
views
How to have two models reference each other Django
I have the following code:
class Game(models.Model):
title = models.CharField(max_length=50)
summery = models.CharField(max_length=500)
key = models.IntegerField()
pin = models....
- 11.3k
34
votes
5
answers
50k
views
How can my django model DateField add 30 days to the provided value?
as the title suggests. I want to add 30 days to the DateField field. This is auto populated on creation of record using auto_now_add=True
Any ideas how to go about doing this?
Thanks
- 41k
34
votes
7
answers
36k
views
Django model instances primary keys do not reset to 1 after all instances are deleted
I have been working on an offline version of my Django web app and have frequently deleted model instances for a certain ModelX.
I have done this from the admin page and have experienced no issues. ...
- 905
32
votes
4
answers
44k
views
How to set initial data for Django admin model add instance form?
How can I set an initial value of a field in the automatically generated form for adding a Django model instance, before the form is displayed? I am using Django 1.3.1.
My model is the following:
...
- 3,918
31
votes
3
answers
36k
views
Better option to check if a particular instance exists django
Which of the two is a better and efficient option to check if an instance exists. There can only be one record returned at most.
1) Use the filter option and see if it exists:
x = MyObject.objects....
- 11k
31
votes
2
answers
20k
views
Access fields in Django intermediate model
I'm creating a Person Group and Membership as described in Django docs for intermediate model.
class Person(models.Model):
name = models.CharField(max_length=128)
def __unicode__(self):
...
- 2,789
30
votes
4
answers
31k
views
Override django's model delete method for bulk deletion
I'm overriding Django's model delete method in order to delete orphan files in the disk for image fields, something like this:
class Image(models.Model):
img = models.ImageField(upload_to=...
- 1,329
28
votes
3
answers
25k
views
django update_or_create gets "duplicate key value violates unique constraint "
Maybe I misunderstand the purpose of Django's update_or_create Model method.
Here is my Model:
from django.db import models
import datetime
from vc.models import Cluster
class Vmt(models.Model):
...
- 10.2k
28
votes
3
answers
14k
views
Django model inheritance: Create a subclass using existing super class
I'm using multi-table-inheritance, and want to know how to create an inherited type from an instance of the superclass.
Using the example given in the documentation:
class Place(models.Model):
...
- 5,886
28
votes
3
answers
8k
views
Python/Django: synonym for field "type" in database model (reserved built-in symbol)
I created a django project. It contains a model class with a "type" attribute. I think that "type" is the most appropriate term to describe that field, because it defines the kind of the entry.
...
- 29.5k
27
votes
4
answers
25k
views
How to remove the prefix of a table for a Django model?
I create a new Django app (not project) called Bussinesses, then add following class to the models.py.
class Bussinesses(models.Model):
business_email = models.EmailField()
password = models....
- 8,567
26
votes
1
answer
10k
views
Django MVC pattern for non database driven models?
I'm just working my way through Django, and really liking it so far, but I have an issue and I'm not sure what the typical way to solve it.
Suppose I have a View which is supposed to be updated when ...
- 5,147
26
votes
1
answer
9k
views
Django: Creating a Mixin for Reusable Model Fields
I've got a few fields that I want to add to most every model in my project. For example, these fields are "tracking fields" such as a created date, an update date, and an "active" flag. I'm ...
- 10.5k
25
votes
3
answers
64k
views
Django models filter by foreignkey
I'm having some trouble in filtering objects from a set of models. Here is the problem:
I have 3 classes:
class Autor(models.Model):
nome = models.CharField(max_length=50)
slug = models....
- 353
25
votes
9
answers
50k
views
How to store a dictionary in a Django database model's field
I need to save a dictionary in a model's field. How do I do that?
For example I have this code:
def create_random_bill(self):
name_chars = re.compile("[a-zA-Z0-9 -_]")
bill_name = "".join(...
- 20.3k
24
votes
1
answer
27k
views
Django CharField with no max length
I have a frontend that will be sending bas64 images, I will put those very large strings on a variable and send it to a form. What kind of FormField can I use?
The regular CharFields need a ...
- 11.2k
23
votes
12
answers
40k
views
Error in admin: __str__ returned non-string (type NoneType)
The admin returns this error when trying to add an instance to one of my models. The model itself has a correct str() method and contains no instances yet. Also tried replacing the str() method with a ...
- 2,940
23
votes
5
answers
23k
views
Django ORM how to Round an Avg result
I have a model in which I use Django ORM to extract Avg of values from the table. I want to Round that Avg value, how do I do this?
See below I am extracting Avg price from Prices model grouped by ...
- 515
23
votes
2
answers
8k
views
Django: Using F arguments in datetime.timedelta inside a query
Using Django model syntax, if I do this:
ThatModel.objects.filter(
last_datetime__lte=now + datetime.timedelta(seconds=F("interval")))
I get:
TypeError: unsupported type for timedelta days ...
- 2,272
23
votes
1
answer
12k
views
How do Django Fixtures handle ManyToManyFields?
I'm trying to load in around 30k xml files from clinicaltrials.gov into a mySQL database, and the way I am handling multiple locations, keywords, etc. are in a separate model using ManyToManyFields.
...
- 1,283
23
votes
2
answers
13k
views
Can you add parameters to Django custom admin actions?
For example (not the case, but just to illustrate) if I wanted to add an action to set a specific field in the selected items to X. Is it possible to add an action to allow X to be entered as opposed ...
- 25.6k