Example of custom model field extending ForeignKey - django

Can someone give me an example of extending a ForeignKey model field? I tried like this:
class ForeignKeyField(forms.ModelChoiceField):
def __init__(self, *args, **kwargs):
super(ForeignKeyField, self).__init__(Chain.objects.all(), *args, **kwargs)
def clean(self, value):
return Chain.objects.get(pk=value)
class CustomForeignKey(models.ForeignKey):
description = "key from ndb"
__metaclass__ = models.SubfieldBase
def __init__(self, *args, **kwargs):
super(CustomForeignKey, self).__init__(*args, **kwargs)
def db_type(self, connection):
return "ndb"
def to_python(self, value):
# import pdb; pdb.set_trace()
from google.appengine.api.datastore_types import Key
if isinstance(value, Key) is True:
return value.id()
if value is None:
return
return value
def get_db_prep_save(self, value, connection, prepared=False):
save_value = ndb.Key(API_Chain, value.id).to_old_key()
return save_value
def formfield(self, **kwargs):
return models.Field.formfield(self,ForeignKeyField, **kwargs)
I don't know why but if i use __metaclass__ = models.SubfieldBase the to_python gets called with None values and it says that foreign key cannot be null. If I inherit from models.Field it works but not as a foreign Key.
I would like to see how one can extend the functionality of models.ForeignKey. Thanks.

Do you need SubfieldBase? It does some magic behind the scenes so that the field has a descriptor that calls to_python. ForeignKey has different kind of descriptor. I guess ForeignKey descriptor is overridden by the subfieldbase descriptor. In other words, they arenot compatible.

Related

Django get instance in inline form admin

Have a inline form class:
class ItemColorSelectForm(forms.ModelForm):
def __init__(self, *args, **kwargs):
super(ItemColorSelectForm, self).__init__(*args, **kwargs)
#here i need current object
Inline class:
class ItemColorSelectInline(generic.GenericTabularInline):
model = ColorSelect
extra = 1
form = ItemColorSelectForm
Admin class
class ItemAdmin(admin.ModelAdmin):
inlines = [ItemColorInline,]
Question: how can a get current object in ItemColorSelectForm.
print kwargs return:
{'auto_id': u'id_%s', 'prefix': u'catalog-colorselect-content_type-object_id-__prefix__', 'empty_permitted': True}
Currently accepted solution is not thread safe. If you care about thread safety, never, ever assign an instance to a static class property.
Thread safe solutions are:
For Django 1.7 < 1.9 (possibly earlier versions, unclear):
from django.utils.functional import cached_property
def get_formset(self, *args, **kwargs):
FormSet = super(InlineAdmin, self).get_formset(*args, **kwargs)
class ProxyFormSet(FormSet):
def __init__(self, *args, **kwargs):
self.instance = kwargs['instance']
super(ProxyFormSet, self).__init__(*args, **kwargs)
#cached_property
def forms(self):
kwargs = {'instance': self.instance}
forms = [self._construct_form(i, **kwargs)
for i in xrange(self.total_form_count())]
return forms
return ProxyFormSet
As of Django >= 1.9 it's also possible to pass form_kwargs:
def get_formset(self, *args, **kwargs):
FormSet = super(InlineAdmin, self).get_formset(*args, **kwargs)
class ProxyFormSet(FormSet):
def __init__(self, *args, **kwargs):
form_kwargs = kwargs.pop('form_kwargs', {})
form_kwargs['instance'] = kwargs['instance']
super(ProxyFormSet, self).__init__(
*args, form_kwargs=form_kwargs, **kwargs)
return ProxyFormSet
Above solutions will make an instance kwarg available in the model form:
class InlineForm(forms.ModelForm):
def __init__(self, *args, **kwargs):
super(InlineForm, self).__init__(*args, **kwargs)
print('instance', kwargs['instance'])
Solution:
Override the formset method in Inline class
def get_formset(self, request, obj=None, **kwargs):
InlineForm.obj = obj
return super(InlineAdmin, self).get_formset(request, obj, **kwargs)
To fix: currently accepted solution not safe in multi-thread mode
Arti's solution works, another better option could be:
Instead of passing the current object id into the inline form,
use the object id to create a inline form field within the get_formset().
# admin.py
class TransactionInline(admin.TabularInline):
model = Transaction
form = TransactionInlineForm
def get_formset(self, request, obj=None, **kwargs):
# comment Arti's solution
# TransactionInlineForm.project_id = obj.id
formset = super().get_formset(request, obj, **kwargs)
field = formset.form.declared_fields['purchase']
field.queryset = get_object_or_404(Project, pk=obj.id).products.all()
return formset
# forms.py
class TransactionInlineForm(ModelForm):
purchase = ModelChoiceField(queryset=None, label='Purchase', required=False)
So, there is no need to override the __init__() in form anymore, neither the current object.
works in Django 2.1.7

How can I make all CharField in uppercase direct in model?

I tried to use UpperCase in all my CharField, in all my Django Model.
Today I have some code in my save method:
def save(self, *args, **kwargs):
for field_name in ['razao_social', 'nome_fantasia', 'cidade', 'endereco','bairro', 'uf', 'cli_parc_nomeparc', 'cli_repr_nomerepr']:
val = getattr(self, field_name, False)
if val:
setattr(self, field_name, val.upper())
super(Pessoa, self).save(*args, **kwargs)
But its take some time. There`s any method to put some uppercase=True in my models?
Thanks.
Here is how to override a Django Model Field and make it upper-case as of Django 1.8.
This will:
work by saving the upper-cased value to the database
returns an upper-cased value in the save response.
Here's the code:
from django.db import models
class UpperCaseCharField(models.CharField):
def __init__(self, *args, **kwargs):
super(UpperCaseCharField, self).__init__(*args, **kwargs)
def pre_save(self, model_instance, add):
value = getattr(model_instance, self.attname, None)
if value:
value = value.upper()
setattr(model_instance, self.attname, value)
return value
else:
return super(UpperCaseCharField, self).pre_save(model_instance, add)
If you want to do this in Django rest framework, here's the code:
from rest_framework import serializers
class UpperCaseSerializerField(serializers.CharField):
def __init__(self, *args, **kwargs):
super(UpperCaseSerializerField, self).__init__(*args, **kwargs)
def to_representation(self, value):
value = super(UpperCaseSerializerField, self).to_representation(value)
if value:
return value.upper()
The correct way would be to define custom model field:
from django.db import models
from django.utils.six import with_metaclass
class UpperCharField(with_metaclass(models.SubfieldBase, models.CharField)):
def __init__(self, *args, **kwargs):
self.is_uppercase = kwargs.pop('uppercase', False)
super(UpperCharField, self).__init__(*args, **kwargs)
def get_prep_value(self, value):
value = super(UpperCharField, self).get_prep_value(value)
if self.is_uppercase:
return value.upper()
return value
and use it like so:
class MyModel(models.Model):
razao_social = UpperCharField(max_length=50, uppercase=True)
# next field will not be upper-cased by default (it's the same as CharField)
nome_fantasia = UpperCharField(max_length=50)
# etc..
you also need to resolve south migration issues (if necessary), by adding this code:
from south.modelsinspector import add_introspection_rules
add_introspection_rules([
(
[UpperCharField],
[],
{
"uppercase": ["uppercase", {"default": False}],
},
),
], ["^myapp\.models\.UpperCharField"])
(path in the last line depends on the field class localization. Please read the south docs for explanation.)
Although there's a small downside when you use shell for instance to create model object and save it in variable:
my_object = MyModel.objects.create(razao_social='blah')
print my_object.razao_social
you won't get upper-cased value. You need to retrieve the object from the database. I will update this post, when I find out how to resolve this issue as well.
Instead of defining a custom field, you can also use the RegexValidator:
from django.core.validators import RegexValidator
...
my_field = models.CharField(
max_length=255,
validators=[RegexValidator('^[A-Z_]*$',
'Only uppercase letters and underscores allowed.')],
)
(see Docs)
Here is my dirty and easier solution without having to deal with migrations:
char_fields = [f.name for f in self._meta.fields if isinstance(f, models.CharField) and not getattr(f, 'choices')]
for f in char_fields:
val = getattr(self, f, False)
if val:
setattr(self, f, val.upper())
super(Cliente, self).save(*args, **kwargs)
django 4, just override the save() method of the model
from django.db import models
class MyModel(models.Model):
my_field = models.CharField(max_length=255)
def save(self, *args, **kwargs):
self.my_field = self.my_field.upper()
super().save(*args, **kwargs)

Django: Passing arguments to ModelField at runtime

I am fairly new to Python + Django and I am stuck with the following problem. I have created a custom ModelField like:
class MyField(models.TextField):
def __init__(self, *args, **kwargs):
super(MyField, self).__init__(*args, **kwargs)
def pre_save(self, model_instance, add):
# custom operations here
# need access to variable xyz
The model using this field looks something like:
class MyModel(models.Model):
my_field = MyField()
def __init__(self, model, xyz, *args, **kwargs):
self.instance = model
# how to pass xyz to ModelField before pre_save gets called?
self.xyz = xyz
def save(self, *args, **kwargs):
if self.instance:
self.my_field = self.instance
Q: Like it says in the comment, is there a way to pass a variable to the ModelField instance at runtime, ideally before my_field.pre_save() gets called?
You don't need to do anything to pass the xyz variable on -- it is an instance variable on the model, so it is already present in the model_instance variable that gets passed to pre_save()
class MyField(models.TextField):
def pre_save(self, model_instance, add):
...
# Access model_instance.xyz here
...
# Call the superclass in case it has work to do
return super(MyField, self).pre_save(model_instance, add)

Make a Django model read-only?

What it says on the tin. Is there a way to make a Django model read-only?
By this I mean a Django model in which once records have been created, they can't be edited.
This would be useful for a model that records transaction history.
You can override the model's save method and check whether it's an existing entity, in which case you won't save any changes:
def save(self, *args, **kwargs):
if self.id is None:
super(ModelName, self).save(*args, **kwargs)
So in this example you only save the changes when the entity has not got an id yet, which is only the case when it's a new entity that hasn't been inserted yet.
You can override the save method and not call super if you wanted to. That'd be a fairly easy way of accomplishing this.
# blatantly ripped the save from another answer, since I forgot to save original model
def save(self, *args, **kwargs):
if self.id is None:
super(ModelName, self).save(*args, **kwargs)
def delete(self, *args, **kwargs):
return
You should probably also raise an exception if a delete or update is attempting to occur instead of simply returning. You want to signal the user what is happening - that the behaviour isn't valid.
In addition to other solutions: If your main goal is to avoid write access from the admin, you can modify the used admin class so that nobody has an add/change permission:
class HistoryAdmin(admin.ModelAdmin):
def has_add_permission(self, request):
return False
def has_change_permission(self, request, obj=None):
return False
def has_delete_permission(self, request, obj=None):
return False
If you don't want an attempt to modify a record to fail silently:
def save(self, *args, **kwargs):
if self.pk:
(raise an exception)
super(YourModel, self).save(*args, **kwargs)
def delete(self, *args, **kwargs):
(raise an exception)

Django: Check if foreign key attribute is set

I have the following model:
class A(models.Model):
name = models.CharField(max_length=50)
content_type = models.ForeignKey(ContentType)
This model is supposed to be the root model in some inheritance tree and content_type attribute is a kind of a hint about what type is really stored.
Obviously, I should calculate content_type transparently upon A instance creation. I think, in __init__. But there is a problem - there are two main contexts in which A instances are created:
a = A(name='asdfdf') # here we must fill in content_type
by QuerySet machinery with *args tuple. In this case I shouldn't fill in content_type
So, I'm trying to write:
def __init__(self, *args, **kwargs):
super(A, self).__init__(*args, **kwargs)
if self.content_type is None: # << here is the problem
self.content_type = ContentType.objects.get_for_model(self)
The thing is self.content_type is ReverseSingleRelatedObjectDescriptor instance with __get__ overriden so that it throws in case value is not set. Yes, I can do following:
def __init__(self, *args, **kwargs):
super(A, self).__init__(*args, **kwargs)
try:
self.content_type
except Exception, v:
self.content_type = ContentType.objects.get_for_model(self)
But I don't like it. Is there a more 'polite' way to check if the ForeignKey attribute is set?
Does it work if you examine self.content_type_id instead of self.content_type?