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It is impossible to add a non-nullable field 'id' to video without specifying a default

This is my models.py
from ast import Delete
from email.policy import default
from django.db import models
from django.contrib.auth.models import User
class Video(models.Model):
user = models.ForeignKey(User, on_delete=models.CASCADE)
title=models.CharField(max_length=100, null=False)
description=models.TextField(max_length=1000,null=True)
video=models.FileField(upload_to="video/%y",null=False)
def __str__(self):
return self.title
class Euser(models.Model):
user = models.OneToOneField(User, on_delete=models.CASCADE)
phone = models.CharField(max_length=10,null=True)
birthdate = models.DateField(null=True,)
profile_pic = models.ImageField(null=True, )
cover_pic = models.ImageField( null=True, upload_to="images/%y")
def __str__(self):
return self.phone
when i try to makemigrations
It is impossible to add a non-nullable field 'id' to video without specifying a default. This is because the database needs something to populate existing rows.
Please select a fix:
Provide a one-off default now (will be set on all existing rows with a null value for this column)
Quit and manually define a default value in models.py.
This error occurs...
Please suggest me what should i do
and also suggest me about any changes in model

For a particular model, in the database, if records already exist and add new fields to the model then it shows such an error. To overcome this problem, you have to set the new field as blank=True and null=True or you can set some default value to the new field using default='some_value'.

django: how to update models

I want the update a model in django
this is a model in models.py:
class Article(models.Model):
CATEGOTY = (
('programming', 'programming'),
('other', 'other')
)
title = models.CharField(max_length=100, null=False)
content = models.TextField(null=False)
category = models.CharField(max_length=100, choices=CATEGOTY, null=False)
creation = models.DateTimeField(auto_now_add=True)
author = models.ForeignKey(Author, on_delete=models.CASCADE)
def __str__(self):
return self.title
for example i want to add slug in this model like this:
slug = models.SlugField(max_length=100, null=False)
but when i display py manage.py makemigrations; this is shown to me:
Please select a fix:
1) Provide a one-off default now (will be set on all existing rows with a null value for this column)
2) Quit, and let me add a default in models.py
what should I enter if I select option 1?
if i type datetime.date.today() It gives me an error that says:
TypeError: function missing required argument 'year' (pos 1)

When you add a mandatory field when the table is not empty, you need to provide the system with information to populate the new field.
For this, you have 2 choices:
define a rule for a default value
choose option 2 and, for each row, you will be asked to enter a value
For option 1, maybe you should use slugify() function (from django.utils.text module)
What I do sometimes is add the rule in the model's definitioon, to ensure existing rows will be updated, then I remove the constraints and manage values by the application.

You can delete your previous migrations then try to migrate again I think it will do the work. but the problem is it will delete all the records.

Whats the meaning of the model default params?

When I read a project, there I saw the params for create the field:
class Task(models.Model):
title = models.CharField('标题', max_length=100)
description = models.TextField('描述')
completed = models.BooleanField('是否完成', default=False)
create_date = models.DateTimeField('创建时间', auto_now_add=True)
Such as: title = models.CharField('标题', max_length=100)
I don't understand the 标题 here has what function.

The first parameter of a Field in django is the verbose name
A human-readable name for the field. If the verbose name isn’t given, Django will automatically create it using the field’s attribute name, converting underscores to spaces

You will have couple of fields , one default value for that model column , one max length of that model column , alias name for that model column , and if that column is primary that will also be there

it's the field name displayed in the admin panel forms or if you use ModelForm for you website forms

FieldError: Unknown field(s) (created_at, modified_at) specified for Account

I am trying to create a timestamp for my model Account, but I don't want my two time stamps (created_at and modified_at) to be editable or even viewable by the user. Everything works fine and as expected until I add editable=False to the created_at and modified_at fields. Here is my model:
class Account(models.Model):
account_name = models.CharField(max_length=25)
active = models.BooleanField(default=True)
created_at = models.DateTimeField(null=True, blank=True, editable=False)
modified_at = models.DateTimeField(null=True, blank=True, editable=False)
def save(self):
if self.id:
self.modified_at = datetime.datetime.now()
else:
self.created_at = datetime.datetime.now()
super(Account, self).save()
class Meta:
ordering = ('id',)
Here is the obscure error I get when I try to do anything (migrate, runserver, etc):
django.core.exception.FieldError: Unknown field(s) (created_at, modified_at) specified for Account
As soon as I remove editable=False from both fields, everything works fine. Is this a Django bug? Is there a better way to make the field non-viewable and non-editable by the user?
I am using Django 1.9 and Python 3.6.1. Thanks for the help, let me know if you need me to post anything else (views, serializers, etc).
EDIT
Full traceback: https://pastebin.com/YEQACX5z
Accounts Form:
class AccountForm(ModelForm):
class Meta:
model = Account
fields = ['account_name', 'active', 'created_at', 'modified_at']

You could just do,
created_at = models.DateTimeField(auto_now_add=True)
and
modified_at = models.DateTimeField(auto_now=True)
From the docs,
DateField.auto_now¶
Automatically set the field to now every time the object is saved. Useful for “last-modified” timestamps. Note that the current date is always used; it’s not just a default value that you can override.
The field is only automatically updated when calling Model.save(). The field isn’t updated when making updates to other fields in other ways such as QuerySet.update(), though you can specify a custom value for the field in an update like that.
DateField.auto_now_add¶
Automatically set the field to now when the object is first created. Useful for creation of timestamps. Note that the current date is always used; it’s not just a default value that you can override. So even if you set a value for this field when creating the object, it will be ignored.
So, no need to add editable=False, its already non-editable.
Also, remember to remove your save() method override since it's trying to modify those fields.
If you want to be able to modify this field, set the following instead of auto_now_add=True:
For DateField: default=date.today - from datetime.date.today()
For DateTimeField: default=timezone.now - from django.utils.timezone.now()
The default form widget for this field is a TextInput. The admin adds a JavaScript calendar, and a shortcut for “Today”. Includes an additional invalid_date error message key.

MySQL gives an "Unknown column 'user.id' in 'field list'" error using Django's automatic id

I have my User model set up with no primary key so that the automatic id will be used instead. However, when I try to access it using Django's "_set" notation when it is referenced through a foreign key:
def postDetails(request, pk)
post = Post.objects.get(pk=pk)
if post.user_set.all(): # Errors on this line
[...]
I get an error from MySQL:
OperationalError at /webApp/postDetail/42/ (1054,
"Unknown column 'user.id' in 'field list'")
What am I doing wrong? Should I be accessing it differently? Are there limitations to the automatic id?
Model for reference:
class Post(models.Model):
name = models.CharField(max_length=128)
blog = models.ForeignKey('Blog')
active = models.BooleanField(blank=True)
created_date = models.DateTimeField()
class Meta:
managed = False
db_table = 'post'
def __unicode__(self):
return self.name
class User(models.Model):
level = models.ForeignKey(Level)
post = models.ForeignKey(Post)
name = models.CharField(max_length=64)
note = models.CharField(max_length=4096)
active = models.BooleanField(blank=True, default=True)
class Meta:
managed = False
db_table = 'user'
Something else that I thought to include: I did run syncdb before running this.

EDIT : wrong answer. check comments below
The problem is that you have managed set to False. According to the documentation
If False, no database table creation or deletion operations will be performed for this model. This is useful if the model represents an existing table or a database view that has been created by some other means. This is the only difference when managed=False. All other aspects of model handling are exactly the same as normal. This includes
Adding an automatic primary key field to the model if you don’t declare it. To avoid confusion for later code readers, it’s recommended to specify all the columns from the database table you are modeling when using unmanaged models.
You will need to define the primary key as this is not done by default anymore.

Not 100% sure, but I think even though Django will add the id field to the model class, that field will not propagate to the DB with syncdb.
One way to try it would be to rename the existing User table, run syncdb and see if the User table is created. If not (which is likely because of the managed flag) try again with managed=True. If the id field appears in this case then my guess is you'll have to add it manually to the User table with the same parameters as the automatically created one.