I wonder if is it possible to add some conditional fields in django.
Say I have a category model which has an ID, name and description fields.
What I would like is to add a many-to-many field in my Product model that links it with the Category ID model... and as a helping reference show what the name of that Category would be.
I know I could just link it to the category name, but my real scenario is a bit more complex and I would really need to display a second field based on the selection in another !
Many thanks!
In addition to Daniel's answer: If you just want to customize the representation of the objects in a ModelChoiceField (and not change it in general what you would do with the __unicode__ method): The field class has method label_from_instance, which returns by default the object's unicode value, but you can override it as you like:
class CategoryChoiceField(forms.ModelChoiceField):
def label_from_instance(self, obj):
return "%s %s" % obj.pk, obj.name
That's not a conditional field. If I understand you correctly, all you really need is to customise the display of the related item, so that it shows the name field rather than the raw ID. Luckily, that is what Django will do by default if you define a __unicode__ method on the Category model, which returns the value you want to display instead of the ID.
Related
In Django SimpleHistoryAdmin List View are 5 default columns (OBJECT, DATE/TIME, COMMENT, CHANGE_BY, CHANGE_REASON). I may add another column adding it to the history_list_display but name of this additional column is displayed as it's name in code, for example first_name. Is there an easy way to display it as First Name?
the column will show the verbose_name defined in the field definition on the Model.
If you do not have access to the Model but to the ModelAdmin, you can try to do something like:
class SimpleHistoryAdmin(...):
...
def _myfirst_name(self, instance):
return instance.first_name
_myfirst_name.short_description = "DESIRED FIELD LABEL"
You can user gettext and it's variants to provide translations for your custom label if needed.
Hope this helps.
In a Django app, I'm having a model Bet which contains a ManyToMany relation with the User model of Django:
class Bet(models.Model):
...
participants = models.ManyToManyField(User)
User should be able to start new bets using a form. Until now, bets have exactly two participants, one of which is the user who creates the bet himself. That means in the form for the new bet you have to chose exactly one participant. The bet creator is added as participant upon saving of the form data.
I'm using a ModelForm for my NewBetForm:
class NewBetForm(forms.ModelForm):
class Meta:
model = Bet
widgets = {
'participants': forms.Select()
}
def save(self, user):
... # save user as participant
Notice the redefined widget for the participants field which makes sure you can only choose one participant.
However, this gives me a validation error:
Enter a list of values.
I'm not really sure where this comes from. If I look at the POST data in the developer tools, it seems to be exactly the same as if I use the default widget and choose only one participant. However, it seems like the to_python() method of the ManyToManyField has its problems with this data. At least there is no User object created if I enable the Select widget.
I know I could work around this problem by excluding the participants field from the form and define it myself but it would be a lot nicer if the ModelForm's capacities could still be used (after all, it's only a widget change). Maybe I could manipulate the passed data in some way if I knew how.
Can anyone tell me what the problem is exactly and if there is a good way to solve it?
Thanks in advance!
Edit
As suggested in the comments: the (relevant) code of the view.
def new_bet(request):
if request.method == 'POST':
form = NewBetForm(request.POST)
if form.is_valid():
form.save(request.user)
... # success message and redirect
else:
form = NewBetForm()
return render(request, 'bets/new.html', {'form': form})
After digging in the Django code, I can answer my own question.
The problem is that Django's ModelForm maps ManyToManyFields in the model to ModelMultipleChoiceFields of the form. This kind of form field expects the widget object to return a sequence from its value_from_datadict() method. The default widget for ModelMultipleChoiceField (which is SelectMultiple) overrides value_from_datadict() to return a list from the user supplied data. But if I use the Select widget, the default value_from_datadict() method of the superclass is used, which simply returns a string. ModelMultipleChoiceField doesn't like that at all, hence the validation error.
To solutions I could think of:
Overriding the value_from_datadict() of Select either via inheritance or some class decorator.
Handling the m2m field manually by creating a new form field and adjusting the save() method of the ModelForm to save its data in the m2m relation.
The seconds solution seems to be less verbose, so that's what I will be going with.
I don't mean to revive a resolved question but I was working a solution like this and thought I would share my code to help others.
In j0ker's answer he lists two methods to get this to work. I used method 1. In which I borrowed the 'value_from_datadict' method from the SelectMultiple widget.
forms.py
from django.utils.datastructures import MultiValueDict, MergeDict
class M2MSelect(forms.Select):
def value_from_datadict(self, data, files, name):
if isinstance(data, (MultiValueDict, MergeDict)):
return data.getlist(name)
return data.get(name, None)
class WindowsSubnetForm(forms.ModelForm):
port_group = forms.ModelMultipleChoiceField(widget=M2MSelect, required=True, queryset=PortGroup.objects.all())
class Meta:
model = Subnet
The problem is that ManyToMany is the wrong data type for this relationship.
In a sense, the bet itself is the many-to-many relationship. It makes no sense to have the participants as a manytomanyfield. What you need is two ForeignKeys, both to User: one for the creator, one for the other user ('acceptor'?)
You can modify the submitted value before (during) validation in Form.clean_field_name. You could use this method to wrap the select's single value in a list.
class NewBetForm(forms.ModelForm):
class Meta:
model = Bet
widgets = {
'participants': forms.Select()
}
def save(self, user):
... # save user as participant
def clean_participants(self):
data = self.cleaned_data['participants']
return [data]
I'm actually just guessing what the value proivded by the select looks like, so this might need a bit of tweaking, but I think it will work.
Here are the docs.
Inspired by #Ryan Currah I found this to be working out of the box:
class M2MSelect(forms.SelectMultiple):
def render(self, name, value, attrs=None, choices=()):
rendered = super(M2MSelect, self).render(name, value=value, attrs=attrs, choices=choices)
return rendered.replace(u'multiple="multiple"', u'')
The first one of the many to many is displayed and when saved only the selected value is left.
I found an easyer way to do this inspired by #Ryan Currah:
You just have to override "allow_multiple_selected" attribut from SelectMultiple class
class M2MSelect(forms.SelectMultiple):
allow_multiple_selected = False
class NewBetForm(forms.ModelForm):
class Meta:
model = Bet
participants = forms.ModelMultipleChoiceField(widget=M2MSelect, required=True, queryset=User.objects.all())
I understand that, by default, Django auto-populates id for each form field upon rendering with the format id_for_%s. One can modify the format by providing the auto_id argument with a different format as its value to the Form constructor.
That's not exactly what I am looking for, however. What I want to accomplish is changing the id of just one of the many fields in my form. Also, the solution should not break the use of form = MyForm(request.POST).
PS. MyForm is a model form, so each id is derived from its corresponding Model field.
Thanks for helping out.
The forms framework appears to generate labels here:
def _id_for_label(self):
"""
Wrapper around the field widget's `id_for_label` class method.
Useful, for example, for focusing on this field regardless of whether
it has a single widget or a MutiWidget.
"""
widget = self.field.widget
id_ = widget.attrs.get('id') or self.auto_id
return widget.id_for_label(id_)
id_for_label = property(_id_for_label)
Which means you can just supply your field widget with an "id" key to set it to whatever you'd like.
foo = forms.CharField(widget=forms.TextInput(attrs={'id': 'foobar'}))
Or override init and set the attrs after form initialization.
I don't see how this could break a form as django's forms framework isn't ever aware of HTML ids (that data is not passed to the server...)
I have a reasonably complex custom Django model method. It's visible in the admin interface, and I would now like to make it sortable in the admin interface too.
I've added admin_order_field as recommended in this previous question, but I don't fully understand what else I need to do.
class Book(models.Model):
id = models.IntegerField(primary_key=True)
title = models.CharField(max_length=200)
library_id = models.CharField(max_length=200, unique=True)
def current_owner(self):
latest_transaction = Transaction.objects.filter(book=self)[:1]
if latest_transaction:
if latest_transaction[0].transaction_type==0:
return latest_transaction[0].user.windows_id
return None
current_owner.admin_order_field = 'current_owner'
Currently, when I click on the current_owner field in the admin interface, Django gives me
FieldError at /admin/books/book/
Cannot resolve keyword 'current_owner' into field
Do I need to make a BookManager too? If so, what code should I use? This isn't a simple Count like the example in the previous question, so help would be appreciated :)
Thanks!
The Django admin won't order models by the result of a method or any other property that isn't a model field (i.e. a database column). The ordering must be done in the database query, to keep things simple and efficient.
The purpose of admin_order_field is to equate the ordering of a non-field property to the ordering of something that is a field.
For example, a valid values current_owner.admin_order_field could be id, title or library_id. Obviously none of these makes sense for your purpose.
One solution would be to denormalise and always store current_owner as a model field on Book; this could be done automatically using a signal.
You can't do this. admin_order_field has to be a field, not a method - it's meant for when you have a method that returns a custom representation of an underlying field, not when you do dynamic calculations to provide the value. Django's admin uses the ORM for sorting, and that can't sort on custom methods.
From the admin panel I want to populate a slug field based on a certain text field
eg.
Title: My Awesome Page
would automaticaly populate
Slug: my_awesome_page
There used to be a prepoulate_from option for the SlugField up to 0.96. It became an admin option after that. See here for reference on that.
Alternatively, you could override the model's save method to calculate the value of the slug field on save().
This question may be helpful, too.
There is also an app called django-autoslug which provides a field type AutoSlugField. Using that, you could have:
class Something(models.Model):
title = models.CharField(max_lenght=200)
slug = AutoSlugField(populate_from='title')
...
This AutoSlugField has many nice features, such as generating a slug so that it is unique either globally of combined with some other field (maybe a category or the year part of a DateTimeField).
See http://pypi.python.org/pypi/django-autoslug for further details.