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I'm learning Django from Tango with Django but I keep getting this error when I type:
python manage.py makemigrations rango
python manage.py migrate
This is the output:
django.db.utils.IntegrityError: UNIQUE constraint failed: rango_category__new.slug
Models.py:
from django.db import models
from django.template.defaultfilters import slugify
class Category(models.Model):
name = models.CharField(max_length=128, unique=True)
views = models.IntegerField(default=0)
likes = models.IntegerField(default=0)
slug = models.SlugField(unique=True)
def save(self, *args, **kwargs):
self.slug = slugify(self.name)
super(Category, self).save(*args, **kwargs)
def __unicode__(self):
return self.name
class Page(models.Model):
category = models.ForeignKey(Category)
title = models.CharField(max_length=128)
url = models.URLField()
views = models.IntegerField(default=0)
def __unicode__(self):
return self.title
–
The reason for this constrain could be that you didn't have any field called slug in Category class when you have initially migrated it (First Migration), and after adding this field in the model, when you ran makemigrations, you have set default value to something static value(i.e None or '' etc), and which broke the unique constrain for the Category's table's slug column in which slug should be unique but it isn't because all the entry will get that default value.
To solve this, you can either drop the database and migration files and re-run makemigrations and migrate or set a unique default value like this:
slug = models.SlugField(unique=True, default=uuid.uuid1)
Edit:
According to Migrations that add unique fields, modify your migration file to overcome unique constrain. For example, modify your migration file (which added the slug field to the model) like this:
import uuid
from app.models import Category # where app == tango_app_name
class Migration(migrations.Migration):
dependencies = [
('yourproject', '0003_remove_category_slug'),
def gen_uuid(apps, schema_editor):
for row in Category.objects.all():
row.slug = uuid.uuid4()
row.save()
operations = [
migrations.AddField(
model_name='category',
name='slug',
field=models.SlugField(default=uuid.uuid4),
preserve_default=True,
migrations.RunPython(gen_uuid),
migrations.AlterField(
model_name='category',
name='slug',
field=models.SlugField(default=uuid.uuid4, unique=True),
–
–
–
–
I got a field with attribute unique, which was not unique [eg 2-time same value]
python3 manage.py migrate --fake
python3 manage.py makemigrations
python3 manage.py migrate
this did the trick
This means a slug should be unique. You may have some data in your model. You need to delete all the data in that model and you need to migrate again.
In this situation, you have two ways to fix the error;
You need to delete it from the Django admin site. More often than not, it may give an error when you are trying to open the model.
Open command prompt
move to project -> py manage.py shell -> from yourappname.models import modelname -> modelname.objects.delete()
Here if you define a product manager for your model. Then you have to define a delete function. Later you should makemigrate, migrate and continue with the second way
I just met this simiilar error: Django UNIQUE constraint failed. I tried examine the code for very long time, but didn't solve it. I finally used SQLiteStudio to examine the data, and found the data is problematic: I unintentionally added two SAME instances which violates the UNIQUE constraint. To be frank I haven't thought the error could be this naive and simple, and because so it took me a lot of time to find out!
–
I had the same problem and tried all the suggested answers. What finally worked for me was, after I defined the slug field as a URL in models, and ran the makemigrations. I edited the file in makemigrations adding a random number at the end of a basic URL, like this
Generated by Django 3.2.3 on 2022-02-02 20:58
from django.db import migrations, models
from random import randint
class Migration(migrations.Migration):
dependencies = [
('blog', '0002_remove_post_slug1'),
operations = [
migrations.AddField(
model_name='post',
name='slug',
field=models.URLField(blank=True, default='http:/salpimientapa.com/' + str(randint(100000,999999))),
After I ran
python manage.py migrate
I edit the slug as a SlugModel and ran the makemigrations and migrate again
i have this error too ,
i did delete my database in djangoProject ( for example db.sqlite3 )
and then run
python manage.py makemigrations
python manage.py migrate
It's an Integrity Error probably because the migration will temper with the already exiting data in the database.
I had this error and here's what I did:
Enter in the project folder directory
Open the python interpreter
py manage.py shell
Import your Models
from yourappname.models import model
Delete existing data records in the model
model.objects.all().delete()
Exit the Python Interpreter
exit()
Another thing you could do is to set unique="false" on the affecting field. I think this should work; not so sure.
Deleting migration is not always the best way! In the event, you wish to maintain your db and want to add unique filed to an existing table. Here is a step to bypass the error and still maintain your db records.
Run makemigrations
Edited the migration file and removed unique=True (0039_alter_course_options_rename_created_course_timestamp_and_more).
Before
migrations.AddField(
model_name='content',
name='uuid',
field=models.UUIDField(default=uuid.uuid4, unique=True),
After
migrations.AddField(
model_name='content',
name='uuid',
field=models.UUIDField(default=uuid.uuid4),
Now if you migrate, it should run fine. Next, you need to update all previous records.
Create a custom managements
courses/
├── __init__.py
├── management/
│ ├── __init__.py
│ └── commands/
│ ├── __init__.py
│ └── check_uuid_uniqueness.py
├── models.py
├── ...
└── ...
Mine looks like so in the check_uuid_uniqueness.py
from django.apps import apps
from django.core.management.base import BaseCommand
import uuid
class Command(BaseCommand):
help = 'Check the uniqueness of uuid fields in models and generate unique values if necessary.'
def handle(self, *args, **options):
app_name = 'courses'
models = apps.get_app_config(app_name).get_models()
for model in models:
if hasattr(model, 'uuid'):
instances = model.objects.all()
for instance in instances:
list_item = instances.filter(uuid=instance.uuid)
if not instance.uuid or len(list_item)>1:
instance.uuid = uuid.uuid4()
instance.save()
print(model, ' updated: ', instance.uuid)
self.stdout.write(self.style.SUCCESS('UUID uniqueness check completed.'))
Remember, in my case, I was targeting uuid, yours could be slug.
Finally, run the custom command (make sure your python venv is activated)
python manage.py check_uuid_uniqueness
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