I want to remove the relationship between BUser and Profile:
Since the ForeignKey doesn't allow null values I have to iterate (performance is awful!) like this to remove all the relations:
for u in user.profile_set.all():
u.delete()
class Profile(models.Model):
user = models.ForeignKey('BUser')
class BUser(AbstractBaseUser, PermissionsMixin):
username = models.CharField(max_length=40, unique=True)
There is another way to delete all the relations [with a better performance]?
I've tried with:
obj.transparentprofile_set = None
obj.transparentprofile_set.clear()
obj.transparentprofile_set.empty()
but, like I said, since there's not null=True in the ForeignKey I can't use them.
You may use my way, instead touching related model via dotted ORM childs etc objects.childs_set, its more clear and human readable code:
# Get user instance
user = User.objects.get(pk=<uid>)
# Remove profiles
Profile.objects.filter(user=user).delete()
Also, you need remember about related_name Model parameter, so instead profile_set you can use:
class Profile(models.Model):
user = models.Foreignkey(
to=User,
related_name='profiles'
)
# Use related name alias in code
profiles = user.profiles.all()
profile = user.profiles.filter(pk=<profile_id>)
Related
When creating a model in Django like this example:
class Musician(models.Model):
first_name = models.CharField(max_length=50, primary_key=True)
last_name = models.CharField(max_length=50)
instrument = models.CharField(max_length=100)
I noticed some problem (not sure if that's best word) with this approach. There is nothing preventing you from creating something like:
musician = Musician()
musician.save()
effectively having primary_key value equal to None. I would like to force user to set first_name, but frankly speaking I cannot find any simple solution for that.
Is there a way to achieve this?
First of all, don't set first_name as primary key. Just leave the default primary key as the id field. A primary key needs to be unique (a first_name isn't) and should not be something a user enters.
Second, it's true that you cannot enforce a CharField to not be empty at the database level. But you can enforce it at the code level, so that anytime you create a Django Form and validate it, it will raise an error.
In fact, Django does it automatically for you, in your case. By default first_name is a required field, since you didn't set blank=True.
So if you do:
musician = Musician()
musician.full_clean()
this raises a ValidationError.
If you create a form for your model (which is what you need if you want users to create a Musician):
class MusicianForm(ModelForm):
class Meta:
model = Musician
fields = '__all__'
form = MusicianForm(data={})
form.instance.first_name
# ''
form.is_valid()
# False
form.save()
# ValueError: The Musician could not be created because the data didn't validate.
You'll also see that if you register Musician in admin.py for django admin site, you can't leave any of the fields empty. It just won't save.
Model
class SlackPermission(models.Model):
#fields
class GithubPermission(models.Model):
#fields
class Employee(models.Model):
#fields
slack_permission = models.OneToOneField(SlackPermission, on_delete=models.CASCADE, related_name='Slack',default=SlackPermission.objects.get(pk=1))
github_permission = models.OneToOneField(GithubPermission, on_delete=models.CASCADE, related_name='Github',default=GithubPermission.objects.get(pk=1))
Error:
ValueError: Cannot serialize: <GithubPermission: GithubPermission object (1)>
There are some values Django cannot serialize into migration files.
I am creating API just to create Employee. Where there is not option of giving slackpermissions and githubpermissions. How do I give default value in there?
The problem is that the default is calculated immediately, and for migrations, it can not really serialize that.
That bing said, it is not very useful to do this anyway. You can just pass the primary key as default value. This is specified in the documentation on the default=… parameter [Django-doc]:
For fields like ForeignKey that map to model instances, defaults should be the value of the field they reference (pk unless to_field is set) instead of model instances.
So we can write this as:
class Employee(models.Model):
full_name = models.CharField(max_length=100)
first_name = models.CharField(max_length=100)
last_name = models.CharField(max_length=100)
slack_permission = models.OneToOneField(
SlackPermission,
on_delete=models.CASCADE,
related_name='Slack',
default=1
)
github_permission = models.OneToOneField(
GithubPermission,
on_delete=models.CASCADE,
related_name='Github',
default=1
)
Note that you should ensure that there exists an object with that primary key. Therefore it might not be ideal to do that.
The issue here is that you are attempting to set a field value to an object instance. So your default value should be just 1 if you are certain of the pk.
Also, I am not sure the advantage of creating two separate models for these permission values. Seems like they can just be fields in your employee model. Seems like these permissions share identical fields as well which will allow you to flatten them a bit.
How do I use select_related to get the first and last name of the employee class below.
class Employee(models.Model):
"""
Model, which holds general information of an employee.
"""
user = models.OneToOneField(User, related_name='users',
on_delete=models.CASCADE, unique=True)
photo_logo = models.FileField(null=True, blank=True)
Here is how I have implemented my query
emp=Employee.objects.filter(pk=1).select_related('user').values('user_first_name','user_last_name','id')
But I get the following logs after running a print statement in django shell
Cannot resolve keyword 'user_first_name' into field. Choices are: address, address_id, attendance, basic,
Since you need specific fields of user model, you dont need select_related in this case, just use:
emp=Employee.objects.filter(pk=1).values('user__first_name','user__last_name','id')
query.
Note that you shoulduse double underscore __ to perform join.
We should use __ for relation field
emp=Employee.objects.filter(pk=1).select_related(
'user'
).values('user__first_name','user__last_name','id')
I have several models that have a ForeignKey back to a model which has a ForeignKey back to auth User in Django.
models.py
class UserDetails(models.Model):
user = models.ForeignKey(
settings.AUTH_USER_MODEL,
related_name='userdetail_related')
details = models.CharField(max_length=100)
email = models.EmailField(unique=True)
class UserInformation(models.Model):
user = models.ForeignKey(
UserDetails,
related_name='userinfo_related')
info = models.CharField(max_length=100, default='this')
EDIT
My actual code for related_name as per Django Documentation is: related_name='%(app_label)s_%(class)s_related'. I put 'userdetail_related' for ease of explanation here.
Only one UserDetail per User, but many UserInformation per UserDetail.
Where there is an unregistered user and we have captured their email, the email can have UserDetail and UserInformation associated with it for a shopping cart guest checkout system.
In my View I want to access the UserInformation model from self.request.user.
I can access UserDetails in my view via:
details = self.request.user.userdetail_related.filter(
user=self.request.user).first()
But I can't seem to access UserInformation via:
info = self.request.user.userdetail_related.filter(
user=self.request.user).first().userinfo_related.filter(
info='this').first()
The only way I can get this to work is:
details = self.request.user.userdetail_related.filter(
user=self.request.user).first()
info = details.userinfo_related.filter(
info='this').first()
But this surely hits the database twice which I don't want.
Does anyone have a better way of getting the info from UserInformation using the session user 'through' UserDetails?
You can use following:
user_info = UserInformation.objects.filter(user__user=self.request.user).first()
Additionally, when you access UserDetails you don't really need the filter since you are trying to access the related objects from the user itself. So following would work as well.
details = self.request.user.userdetail_related.first()
And as a side note, I think you need OneToOneField here since one user should have only one UserDetails.
As it suggested by #AKS you should use OneToOneField to connect your models to the User. You can do it like this:
class UserDetails(models.Model):
user = models.OneToOneField(
settings.AUTH_USER_MODEL,
related_name='userdetail_related')
details = models.CharField(max_length=100)
class UserInformation(models.Model):
user = models.OneToOneField(
UserDetails,
related_name='userinfo_related')
info = models.CharField(max_length=100, default='this')
Then you can access UserInformation and UserDetails like this:
details = self.request.user.userdetail_related.details
info = self.request.user.userinfo_related.info
To add to the other answers, a few remarks about the layout.
For Model names, best to always use singular (UserDetails -> UserDetail), not plural. Then, for the related name of a ForeignKey, use the plural (because the reverse lookup may find more than one item that have the backwards relationship).
class UserDetail(models.Model):
user = models.ForeignKey(settings.AUTH_USER_MODEL, related_name='details')
details = models.CharField(max_length=100)
class UserInformation(models.Model):
user = models.ForeignKey(settings.AUTH_USER_MODEL, related_name='info')
info = models.CharField(max_length=100, default='this')
Makes it much simpler to access in the views
request.user.infos.all().first()
request.user.details.filter(info__startswith="something")
Also, if practical, add both onto the User object, because "flat is better than nested" .
If every User only has one UserDetail and one UserInformation then its best to use OneToOneFields instead.
I have the following User object as a simple example
class AppUser(AbstractBaseUser, PermissionsMixin):
follows = models.ManyToManyField('self', related_name='follows_users', symmetrical=False)
I want to get all the user's that follow a user. for example
u2.follows.add(u1)
u3.follows.add(u1)
I want to return [u2,u3] as a result for users that follow u1
You need to use the related_name you set in the field definition:
users_who_follow_u1 = u1.follows_user.all()
You should also find a better name for it such as followed_by.