I'm trying to make a custom save function that calculates some values and will store them in another Model to which a ManyToMany relationship exists. From what I can understand from the documentation, I should have a field_set way of accessing all the related objects. However, when I save here, I get the error 'Game' object has no attribute 'heat_set'
I don't see what I'm doing wrong here:
class Game(models.Model)
heat = models.ManyToManyField(Heat)
[...]
def save(self, *args, **kwargs):
super().save(*args, **kwargs)
for heat in self.heat_set.all():
[...]
Since the m2m relation is defined in Game with heat = models.ManyToMany(...), you just need to use:
self.heat.all()
Related
So I have MyModel:
class MyModel(models.Model):
name = models.CharField(_('Name'), max_length=80, unique=True)
...
def save(self, *args, **kwargs):
if MyModel.objects.count() >= 5:
raise ValidationError("Can not have more than 5 MyModels!")
super().save(*args, **kwargs) # Call the "real" save() method.
There are already 5 objects from MyModel on the database.
I have a page where I can edit them all at the same time with a formset.
When I change one or more of them, I will get the Validation Error "Can not have more than 5 MyModels!".
Why is this happenning? I tought the formset was supposed to edit the existing objects, but it appears to be writing a new one and deleting the old one.
What is really happening when I do a formset.save() on the database?
Do I have to remove the save() method?
The save method inside the Model is called regardless you are creating or editing. Although you can distinguish between them by checking if the object has a primary key, like this:
if not self.pk and MyModel.objects.count() >= 5:
If you want more sophisticated control over validation, I suggest putting them in the forms. Specially if you want to limit the number of formset, you can check this documentation.
I want to update fields in django admin site following the modification by the user of a given foreignkey field. I seek a way to trigger the event straight after foreignkey modification; not before/after save.
I looked for the creation of a custom signal through sender/receiver. Also I tried to find a similar signal as the m2m_changed. Perhaps one of these path could be the solution.
class Variety(models.Model):
specific_name = models.ForeignKey(CatalogList, on_delete=models.CASCADE)
def update_other_field(self):
#DO SOMETHING EACH TIME specific_name IS MODIFIED
Is there a way to trigger an event directly after a foreignkey is modified?
You can override save method of "parent" model :
class CatalogList(models.Model):
def save(self, *args, **kwargs):
super().save(*args, **kwargs) # Call normal save method
# Then do what you want with variety_set reverse relation
I have an abstract BaseModel from which many models will inherit the behavior to initialize attributes values from the constructor:
class BaseModel(models.Model):
def __init__(self, *args, **kwargs):
super().__init__(*args, **kwargs)
for key in kwargs:
setattr(self, key, kwargs[key])
class Meta:
abstract = True
Then, I try to initialize one of its specializations like this:
BaseModelSon(attr1=val1, attr2=val2, ...)
Is this a good practice? Do you know any other way to achieve this dynamic initialization for Django models?
You can already create regular Django model instances with
MyModel(field1='value1', field2='value2')
so I don't think your __init__ method is necessary.
Also you'll probably find useful Model.objects.create() method for new Django models instances creation:
instance = MyModel.objects.create(field1='value1', field2='value2'...)
If there are some auto-generated fields (for example, id or some date with auto_now_add=True option) — you'll get their values in instance if you have used Model.objects.create().
I am looking to create a duplicate instance each time a user tries to update an instance. The existing record is untouched and the full update is saved to the new instance.
Some foreign keys and reverse foreign keys must also be duplicated. The Django documentation
talks about duplicating objects, but does not address reverse foreign keys.
Firstly, is there an accepted way of approaching this problem?
Secondly, I am unsure whether it's best to overwrite the form save method or the model save method? I would want it to apply to everything, regardless of the form, so I assume it should be applied at the model level?
A simplified version of the models are outlined below.
class Invoice(models.Model):
number = models.CharField(max_length=15)
class Line(models.Model):
invoice = models.ForeignKey(Invoice)
price = models.DecimalField(max_digits=15, decimal_places=4)
Here's my shot at it. If you need it to duplicate every time you make any changes, then override the model save method. Note that this will not have any effect when executing .update() on a queryset.
class Invoice(models.Model):
number = models.CharField(max_length=15)
def save(self, *args, **kwargs):
if not self.pk:
# if we dont have a pk set yet, it is the first time we are saving. Nothing to duplicate.
super(Invoice, self).save(*args, **kwargs)
else:
# save the line items before we duplicate
lines = list(self.line_set.all())
self.pk = None
super(Invoice, self).save(*args, **kwargs)
for line in lines:
line.pk = None
line.invoice = self
line.save()
This will create a duplicate Invoice every time you call .save() on an existing record. It will also create duplicates for every Line tied to that Invoice. You may need to do something similar every time you update a Line as well.
This of course is not very generic. This is specific to these 2 models. If you need something more generic, you could loop over every field, determine what kind of field it is, make needed duplicates, etc.
I want to save an object, so that the M2M get saved. Then I want to read out the M2M fields to do some calculations and set a field on the saved object.
class Item(models.Model):
name = models.CharField(max_length=20, unique=True)
product = models.ManyToManyField(SomeOtherModel, through='SomeTable')
def save(self, *args, **kwargs):
super(Item, self).save(*args, **kwargs)
m2m_items = SomeTable.objects.filter(item = self)
# DO SOME STUFF WITH THE M2M ITEMS
The m2m_items won't turn up,. Is there any way to get these up ?
Some confusion here.
Once you've called super, self.id will have a value.
However, I don't understand the point of your filter call. For a start, you probably mean get rather than filter anyway, as filter gets a queryset, rather than a single instance. But even so, the call is pointless: you've just saved it, so whatever you get back from the database will be exactly the same. What's the point?
Edit after question update OK, thanks for the clarification. However, the model's save() method is not responsible for doing anything with M2M items. They need to be saved separately, which is the job of the form or the view.