I have model with field rules = models.ManyToManyField(blank=True, null=True) and aggregation = models.BooleanField(default=False).
And I want to make aggregation=False in case if rules is empty. In other words, if there are no any rule entered or already stored in database, aggregation field should be always == False.
def save(self, *args, **kwargs):
if not self.rules:
self.aggregation = False
super(MyModel, self).save(*args, **kwargs)
Is this what you mean?
Edit: I see that you might want to check the database also. No problem:
def save(self, *args, **kwargs):
models = MyModel.objects.filter(rules__isnull=False).exists()
if not self.rules and not models:
self.aggregation = False
super(MyModel, self).save(*args, **kwargs)
Related
I'm looking for the most efficient way to implement this kind of mechanism in Django model.
Let's assume a situation, where there are 2 very simple models:
class FKModel(models.Model):
value = BooleanField()
class AModel(models.Model):
fk = models.ForeignKey(FKModel)
a_value = models.CharField(max_length=150)
def clean(self, *args, **kwargs):
# the line below is incorrect
if not self.fk.value: # <--- how to do this in a proper way?
raise ValidationError('FKModel value is False')
super(AModel, self).clean(*args, **kwargs)
def save(self, *args, **kwargs):
self.full_clean()
super(AModel, self).save(*args, **kwargs)
I know, that I can do somethink like FKModel.objects.all()/.get(), but I don't think it is the best solution (as it requires additional requests to database).
I am not sure what you try to do in your clean() method, but I assume you are trying to constrain a not null condition for the foreign key. All fields are not null constrained by default, and you have to set null=False and blank=False if you want the field to accept nulls:
class AModel(models.Model):
fk = models.ForeignKey(FKModel, null=True, blank=True)
a_value = models.CharField(max_length=150)
If you want to constrain a not null condition for a field by hand, you should do it like this:
class FKModel(models.Model):
value = BooleanField()
class AModel(models.Model):
fk = models.ForeignKey(FKModel)
a_value = models.CharField(max_length=150)
def clean(self, *args, **kwargs):
# the line below is correct
if self.fk is None: # <--- this is the proper way?
raise ValidationError('FKModel value is False')
super(AModel, self).clean(*args, **kwargs)
def save(self, *args, **kwargs):
self.full_clean()
super(AModel, self).save(*args, **kwargs)
For retrieving database records and its related records, you use prefetch_related, and you get your record and its related records in one single database hit:
AModel.objects.all().prefetch_related('fk')
I am trying to set the initial value of a field on a form. The field is not part of the model, but when I try and set it to a value the field is blank. From my research it could be because the form is "bound" which makes some sense to me, but in this case the field is not part of the model.
My form:
#Form for editing profile
class CatForm(forms.ModelForm):
pictureid = forms.CharField()
class Meta:
model = Cat
fields = ['name']
def __init__(self, *args, **kwargs):
picid = kwargs.pop("pictureid")
print(picid)
super(CatForm, self).__init__(*args, **kwargs)
self.fields['pictureid'] = forms.CharField(initial=picid, required=False)
The model:
class Cat(models.Model):
name = models.CharField(max_length=34,null=False)
From the view it is called like this:
catform = CatForm(request.POST, pictureid=instance.id)
I was expecting it to set the field to the value of the initial attribute, but it doesn't. I have tried testing it by directly adding a string, but doesn't set.
This is what seems to be working for me:
class CatForm(forms.ModelForm):
class Meta:
model = Cat
fields = ['name']
def __init__(self, *args, **kwargs):
picid = kwargs.pop("pictureid")
super(CatForm, self).__init__(*args, **kwargs)
self.fields['pictureid'] = forms.CharField(initial=picid)
I also needed to drop the "request.POST" from the call to this when initiating the form.
If you want to render the pictureid in GET request, then you can try like this:
catform = CatForm(initial={'pictureid': instance.id})
For GET request, you don't need to override the __init__ method.
But, if you want to use the Catform in POST request, to use the value of pictureid somewhere else(lets say in save method), then you will need to override __init__ method here.
class CatForm(forms.ModelForm):
pictureid = forms.CharField()
class Meta:
model = Cat
fields = ['name']
def __init__(self, *args, **kwargs):
picid = kwargs.pop("pictureid")
print(picid)
super(CatForm, self).__init__(*args, **kwargs)
self.pictureid = picid
def save(self, *args, **kwargs):
print(self.pictureid) # if you want to use it in save method
return super().save(*args, **kwargs)
I have a problem with django app and POSTGRESQL database with the slug field.
Error:
value too long for type character varying(1)
I test my app with sqlite database and everything works fine, but my app does not work in postgresql database. Any ideas why this is the case?
Test 1:
class MyModel(models.Model):
name = models.CharField(max_length=254)
slug_name = models.SlugField(max_length=254)
def save(self, *args, **kwargs):
self.slug_name = slugify(self.name)
super(MyModel, self).save(*args, **kwargs)
Test 2:
class MyModel(models.Model):
name = models.TextField(max_length=500)
slug_name = models.SlugField(max_length=500)
def save(self, *args, **kwargs):
self.slug_name = slugify(self.name)
super(MyModel, self).save(*args, **kwargs)
Test 3:
class MyModel(models.Model):
name = models.TextField()
slug_name = models.SlugField()
def save(self, *args, **kwargs):
self.slug_name = slugify(self.name)
super(MyModel, self).save(*args, **kwargs)
You're trying to insert a value with more that one character into a field specified as character varying(1). SQLite3 will allow this (see https://sqlite.org/datatype3.html) but PostgreSQL will give an error - i.e., it enforces that you have specified the maximum length as 1.
I am trying to override the save method on a model in order to generate a unique, second auto-incrementing id.
I create my class and override the save() method, but for some reason it is erroring out with the following error:
TypeError: %d format: a number is required, not NoneType
Here's the code:
class Person(models.Model):
target = models.OneToOneField(Target)
person = models.OneToOneField(User)
gender = models.CharField(max_length=1)
gender_name = models.CharField(max_length=100)
person_id = models.CharField(max_length=100)
def save(self, *args, **kwargs):
self.person_id = "%07d" % self.id
super(Person, self).save(*args, **kwargs)
Is it because I didn't pass an id parameter and it hasn't saved yet? Is there anyway to generate a value from the id?
Safest and easiest way to achieve what you want is to use a post_save signal because it is fired right after save is called, but before the transaction is committed to the database.
from django.dispatch import receiver
from django.db.models.signals import post_save
#receiver(post_save, sender=Person)
def set_person_id(sender, instance, created, **kwargs):
if created:
instance.person_id = "%07d" % instance.id
instance.save()
Yes, self.id will be Nonein some cases, and then the assignment will fail.
However you cannot just the assignment and the call to super, as suggested in the comments, because then you wouldn't be persisting the assignment to the database layer.
You need to check whether the model has an id and then proceed differently:
def save(self, *args, **kwargs):
if not self.id: # Upon instance creation
super(Person, self).save(*args, **kwargs) # Acquire an ID
self.person_id = "%07d" % self.id # Set the person_id
return super(Person, self).save(*args, **kwargs)
This issues two save operations to the database. You will want to wrap them in a transaction to make sure your database receives these two fields simultaneously.
from django.db import IntegrityError, transaction
class Person(models.Model):
target = models.OneToOneField(Target)
person = models.OneToOneField(User)
gender = models.CharField(max_length=1)
gender_name = models.CharField(max_length=100)
person_id = models.CharField(max_length=100)
def create_person_id(self):
if not self.id: # Upon instance creation
super(Person, self).save(*args, **kwargs) # Acquire an ID
self.person_id = "%07d" % self.id
def save(self, *args, **kwargs):
try:
with transaction.atomic():
self.create_person_id
return super(Person, self).save(*args,**kwargs)
except IntegrityError:
raise # or deal with the error
I agree that signals might be the better option, if not, try using pk instead of id.
class Person(models.Model):
# [ . . . ]
def save(self, *args, **kwargs):
self.person_id = "%07d" % self.pk
super(Person, self).save(*args, **kwargs)
Suppose I had this following code:
class MyModel(models.Model):
...
...
def save(self, *args, **kwargs):
# pre-save edits can go here...
super(MyModel, self).save(*args, **kwargs)
When I create and save a model, MyModel(blah, blah, blah), there is a possibility that
one of the input fields is "None". In the overridden save method, the goal is to check for if a field is none, and if one is, change it to some other default value.
Are the input fields in args or kwargs? And is overriding save() even the proper way to do this?
I was thinking something like this:
def save(self, *args, **kwargs):
if 'username' in args and args['username'] is None:
args['username'] = some_default_value
super(MyModel, self).save(*args, **kwargs)
So where are the input params? args* or **kwargs, thank you.
I think it's better a pre_save signal to see if a input value is None:
from django.db import models
from django.db.models.signals import pre_save
from django.dispatch import receiver
class MyModel(models.Model):
field1 = models.TextField()
field2 = models.IntegerField()
#receiver(pre_save, sender=MyModel)
def mymodel_save_handler(sender, instance, *args, **kwargs):
if instance.field1 is None or instance.field1 == "":
instance.field1 = default_value
If you prefer override save method you can access to the model fields with self
def save(self, *args, **kwargs):
if self.username is None:
self.username = some_default_value
super(MyModel, self).save(*args, **kwargs)