I have a Many to Many field. I'd like to limit the choices the admin shows in its M2M widget.
I have a model like this:
class A(models.Model):
b_field = models.ManyToManyField(B)
class B(models.Model):
available = models.BooleanField()
How do I limit the B objects shown in the widget only to those who have available = True?
The limit_choices_to option might help you,
Sets a limit to the available choices for this field when this field is rendered using a ModelForm or the admin (by default, all objects in the queryset are available to choose). Either a dictionary, a Q object, or a callable returning a dictionary or Q object can be used.
For eg,
class A(models.Model):
b_field = models.ManyToManyField(B, limit_choices_to={'available': True})
Related
I'm building a web crawler contain links blogs etc of x website ... , I have field called number_of_crawled_Links and I want to make the value of that filed is the number of rows in another model Where Links Stored i want the process to be automatically without making request any idea how to do that
You cannot do that in fields directly, but it's good idea to do that as a method.
class ModelA(models.Model):
some_field = models.TextField()
class ModelB(models.Model):
model_a = models.ForeignKey(ModelA, on_delete=models.CASCADE)
def get_some_field_value(self):
return self.model_a.some_field
Then ModelB can get dynamically the value of ModelA field some_field. You can do it with any type of values.
I have a (horrible) database table that will be imported from a huge spreadsheet. The data in the fields is for human consumption and is full of "special cases" so its all stored as text. Going forwards, I'd like to impose a bit of discipline on what users are allowed to put into some of the fields. It's easy enough with custom form validators in most cases.
However, there are a couple of fields for which the human interface ought to be a ChoiceField. Can I override the default form field type (CharField)? (To clarify, the model field is not and cannot be constrained by choices, because the historical data must be stored. I only want to constrain future additions to the table through the create view).
class HorribleTable( models.Model):
...
foo = models.CharField( max_length=16, blank=True, ... )
...
class AddHorribleTableEntryForm( models.Model)
class Meta:
model = HorribleTable
fields = '__all__' # or a list if it helps
FOO_CHOICES = (('square', 'Square'), ('rect', 'Rectangular'), ('circle', 'Circular') )
...?
Perhaps you could render the forms manually, passing the options through the context and make the fields in html.
Take a look at here:https://docs.djangoproject.com/en/4.0/topics/forms/#rendering-fields-manually
I think you can easily set your custom form field as long it will match the data type with the one set in your model (e.g. do not set choices longer than max_length of CharField etc.). Do the following where foo is the same name of the field in your model:
class AddHorribleTableEntryForm(forms.ModelForm):
foo = forms.ChoiceField(choices=FOO_CHOICES)
class Meta:
model = HorribleTable
...
I think this is perfectly fine for a creation form. It's will not work for updates as the values in the DB will most probably not match your choices. For that, I suggest adding a second form handling data updates (maybe with custom permission to restrict it).
UPDATE
Another approach will be to override the forms init method. That way you can handle both actions (create and update) within the same form. Let the user select from a choice field when creating an object. And display as a normal model field for existing objects:
class AddHorribleTableEntryForm(forms.ModelForm):
foo = forms.ChoiceField(choices=FOO_CHOICES)
class Meta:
model = HorribleTable
fields = '__all__' # or a list if it helps
def __init__(self, *args, **kwargs):
super().__init__(*args, **kwargs)
instance = kwargs.get("instance", None)
if instance is None:
self.fields["foo"].widget = forms.widgets.Select(choices=self.FOO_CHOICES)
Working with Django REST Framework I am wondering if it's possible to limit the choices / options of a ManyToMany field on a model to a specific QuerySet?
Using the models below (scroll down to see models), I am curious if it's possible to define this limit in the definition of the model, to achieve the following:
# Having the following Employee instance
emp = Employee(...)
# Should return only the instances with value 'case' in EmployeeSubstitute.type field
emp.substitute_case.all()
# Should return only the instances with value 'phone' in EmployeeSubstitute.type field
emp.substitute_phone.all()
Models:
class Employee(models.Model):
substitute_case = models.ManyToMany(through=EmployeeSubstitute, ...)
substitute_phone = models.ManyToMany(through=EmployeeSubstitute, ...)
class EmployeeSubstitute(models.Model):
from = models.ForeignKey(Employee, ...)
to = models.ForeignKey(Employee, ...)
type = models.CharField(choices=..., ...) # choose between type 'case' and 'phone'
I see that there's the limit_choices_to parameter, but that's not what I am looking for, since that only effects the options shown when using a ModelForm or the admin.
Well, ManyToManyField returns related objects and as docs state
By default, Django uses an instance of the Model._base_manager manager
class when accessing related objects (i.e. choice.question), not the
_default_manager on the related object. This is because Django needs to be able to retrieve the related object, even if it would otherwise
be filtered out (and hence be inaccessible) by the default manager.
If the normal base manager class (django.db.models.Manager) isn’t
appropriate for your circumstances, you can tell Django which class to
use by setting Meta.base_manager_name.
Base managers aren’t used when querying on related models, or when
accessing a one-to-many or many-to-many relationship. For example, if
the Question model from the tutorial had a deleted field and a base
manager that filters out instances with deleted=True, a queryset like
Choice.objects.filter(question__name__startswith='What') would include
choices related to deleted questions.
So if I read it correctly, no, it's not possible.
When you do queries and have through in your ManyToManyField, Django complains you should run these queries on your through model, rather than the "parent". I can't find it in the docs but I remember seeing it a few times.
substitute_case and substitute_phone is something that belongs to substitute and it is it's type. So just do that instead of creating those columns in Employee.
from django.db import models
class SubstituteTypes(models.TextChoices):
case = "case", "case"
phone = "phone", "phone"
class EmployeeSubstituteQueryset(models.QuerySet):
def from_employee(self, e):
return self.filter(_from=e)
def case(self):
return self.filter(type=SubstituteTypes.case)
def phone(self):
return self.filter(type=SubstituteTypes.phone)
class Employee(models.Model):
substitute = models.ManyToManyField(through='EmployeeSubstitute', to='self')
class EmployeeSubstitute(models.Model):
_from = models.ForeignKey(Employee, on_delete=models.CASCADE, related_name='a')
to = models.ForeignKey(Employee, on_delete=models.PROTECT, related_name='b')
type = models.CharField(choices=SubstituteTypes.choices, max_length=5, db_index=True)
objects = EmployeeSubstituteQueryset.as_manager()
Then, once you get your emp object (or only its id), you can do
EmployeeSubstitute.objects.from_employee(emp).case().all()
which is designed in Django philosophy.
Imagine we have a model like that:
class Container(models.Model):
name = models.CharField(max_length=60)
class Element(models.Model):
container = models.ForeignKey(Container, blank=True, null=True)
Container is the One, Element is the many.
In Django admin, if I add a StackedInline with model=Element to the inlines of the Container model admin:
class Inline(admin.StackedInline):
model = Element
class ContainerAdmin(admin.ModelAdmin):
inlines = (Inline,)
admin.site.register(Container, ContainerAdmin)
I end up with a formset allowing me to enter new Element objects on the Add Container form.
Instead, I would like to be given a select widget, to pick existing Element objects.
Is that possible without introducing an extra model ?
I think you should be able to do it like this:
class ContainerAdminForm(forms.ModelForm):
class Meta:
model = Container
fields = ('name',)
element_set = forms.ModelMultipleChoiceField(queryset=Element.objects.all())
class ContainerAdmin(admin.ModelAdmin):
form = ContainerAdminForm
# register and whatnot
I don't know that I have anything like this in my project, but I'll let you know if I find something. You may also have to override the save() method on the form in order to actually save the selected Elements; I don't know if naming the field element_set (or whatever the name of the reverse relation is) will be enough.
I have models similar to the following:
class Band(models.Model):
name = models.CharField(unique=True)
class Event(models.Model):
name = models.CharField(max_length=50, unique=True)
bands = models.ManyToManyField(Band)
and essentially I want to use the validation capability offered by a ModelForm that already exists for Event, but I do not want to show the default Multi-Select list (for 'bands') on the page, because the potential length of the related models is extremely long.
I have the following form defined:
class AddEventForm(ModelForm):
class Meta:
model = Event
fields = ('name', )
Which does what is expected for the Model, but of course, validation could care less about the 'bands' field. I've got it working enough to add bands correctly, but there's no correct validation, and it will simply drop bad band IDs.
What should I do so that I can ensure that at least one (correct) band ID has been sent along with my form?
For how I'm sending the band-IDs with auto-complete, see this related question: Django ModelForm Validate custom Autocomplete for M2M, instead of ugly Multi-Select
You can override the default fields in a ModelForm.
class AddEventForm(forms.ModelForm):
band = forms.CharField(max_length=50)
def clean_band(self):
bands = Band.objects.filter(name=band,
self.data.get('band', ''))
if not bands:
raise forms.ValidationError('Please specify a valid band name')
self.cleaned_data['band_id'] = bands[0].id
Then you can use your autocomplete widget, or some other widget. You can also use a custom widget, just pass it into the band field definition: band = forms.CharField(widget=...)