I have three functions which I need in every Django Model:
def __unicode__(self):
return self.MODELNAME_name
def get_absolute_url(self):
return "/MODELNAME/list/"
def get_fields(self):
return [(field, field.value_to_string(self)) for field in MODELNAME._meta.fields]
The only thing different is the MODELNAME
How can I use inheritance so that I use three functions in one class and other inherit from it?
You could use multiple inheritance:
class CommonFunctions(object):
def __unicode__(self):
return self.MODELNAME_name
def get_absolute_url(self):
return "/MODELNAME/list/"
def get_fields(self):
return [(field, field.value_to_string(self)) for field in MODELNAME._meta.fields]
class ZeModel(models.Model, CommonFunctions):
[...]
x = ZeModel()
x.get_absolute_url()
(Make sure you replace MODELNAME with self.__class__.__name__)
I did not test this, but it should work.
You don't need anything at all. self already refers to the relevant class.
Daniel's answer is right. But if you want a string, that is the name of the current model, you can use:
self._meta.verbose_name_raw
Related
I am trying to display the version field from the below model other than the default str which is field2_name:
Note: This SO link Displaying a specific field in a django form might be more than I need but I am not 100% sure. I tried to implement this but was not successful.
Also note that I tried the example at https://docs.djangoproject.com/en/1.10/ref/forms/fields/ but was not able to get it to work
Model (Generic names):
class CodeVersion(models.Model):
field1= models.ForeignKey(SomeOtherModel, on_delete=models.CASCADE)
field2_name = models.CharField(max_length=256)
field3_description = models.CharField(max_length=1000, blank=True)
version = models.PositiveIntegerField()
def __str__(self):
return self.field2_name
Form:
class VersionsForm(forms.Form):
code_versions = forms.ModelChoiceField(queryset=CodeVersion.objects.none())
def __init__(self, SomeOtherModel_id):
super(VersionsForm, self).__init__()
self.fields['infocode_versions'].queryset = CodeVersion.objects.filter(SomeOtherModel_id=SomeOtherModel_id)
This works - it returns field2_name as it is supposed to.
How do I return version instead - what is the simplest way?
Any help or guidance is appreciated.
From the ModelChoiceField docs:
The __str__ (__unicode__ on Python 2) method of the model will be called to generate string representations of the objects for use in the field’s choices; to provide customized representations, subclass ModelChoiceField and override label_from_instance. This method will receive a model object, and should return a string suitable for representing it. For example:
from django.forms import ModelChoiceField
class MyModelChoiceField(ModelChoiceField):
def label_from_instance(self, obj):
return "My Object #%i" % obj.id
If I got your question correctly you could change object string representation
def __str__(self):
return str(self.version)
You could then inherit ModelChoiceField and override label_from_instance method
or even monkey patch it like this
self.fields['field_name'].label_from_instance = self.label_from_instance
#staticmethod
def label_from_instance(self):
return str(self.value)
In one line :
self.fields['code_versions'].label_from_instance = lambda obj: f"{obj.version}"
Complete example
class VersionsForm(forms.Form):
code_versions = forms.ModelChoiceField(queryset=CodeVersion.objects.none())
def __init__(self, SomeOtherModel_id):
super().__init__()
self.fields['code_versions'].queryset = CodeVersion.objects.filter(SomeOtherModel_id=SomeOtherModel_id)
self.fields['code_versions'].label_from_instance = lambda obj: f"{obj.version}"
The simplest way in this case that I struggled myself:
under your line of code
self.fields['infocode_versions'].queryset = CodeVersion.objects.filter(SomeOtherModel_id=SomeOtherModel_id)
insert this:
self.fields["infocode_versions"].label_from_instance = lambda obj: "%s" % obj.version
Basically, I have to achieve two goals in my project that are currently conflicting with each other in terms of implementation.
The goals are:
Enabling chainable filtering for model instances (my_model.objects.custom_filter1().custom_filter2() etc)
For those tables with is_deleted field, and I want to exclude records marked as deleted, so that I don't have to explicitly filter for deleted records (use my_model.objects.all() instead of my_model.objects.filter(is_deleted = false))
Currently I have the following code:
class MixinManager(models.Manager):
def get_queryset(self):
try:
return self.model.MixinQuerySet(self.model).filter(is_deleted=False)
except FieldError:
return self.model.MixinQuerySet(self.model)
class BaseMixin(models.Model):
objects = MixinManager()
class MixinQuerySet(QuerySet):
pass
class Meta:
abstract = True
class DeleteMixin(BaseMixin):
is_deleted = models.BooleanField(default=False)
class Meta:
abstract = True
class Sms(DeleteMixin):
# core fielrds
# objects = SmsQuerySet.as_manager()
class Meta:
managed = False
db_table = 'sms'
However, my first goal becomes seemingly infeasible. Prior to using abstract classes for achieving the second goal, I had the following code
to solve the second goal:
class SmsQuerySet(models.query.QuerySet):
def filter_1(self, user):
return self.filter(...)
def filter_2(self, user):
return self.filter(...)
def filter_3(self, user):
return self.filter(...)
class Sms(models.Model):
# core fields
objects = SmsQuerySet.as_manager()
This syntax solved my first goal.
THE QUESTION:
The problem is that I can't combine these two structures into one logic, so that I can write:
sms.objects.filter_1().filter_2().filter_3()
so that deleted records are exluded from sms.objects.
If I uncomment the # objects = SmsQuerySet.as_manager() line in the first code snippet, then the objects field of BaseMixin will be ignored and I will end up with deleted records in the final queryset. On the other hand, if I comment the line, than my custom querysets become unreachable.
I hope I succeeded to concisely describe what I am trying to do. Will be very grateful for any hint towards the solution!
It should work
from django.db import models
class SmsQuerySet(models.query.QuerySet):
def filter_1(self, user):
return self.filter(...)
def filter_2(self, user):
return self.filter(...)
def filter_3(self, user):
return self.filter(...)
class MixinManager(models.Manager):
def get_queryset(self):
try:
return SmsQuerySet(self.model).filter(is_deleted=False)
except FieldError:
return SmsQuerySet(self.model)
class Sms(models.Model):
# core fields
objects = MixinManager()
I'm developing django application, and I have such a model structure
class Animal(models.Model):
aul = models.ForeignKey(Aul)
age = models.IntegerField()
def __unicode__(self):
return u'Animal'
class Sheep(Animal):
wool = models.IntegerField()
def __unicode__(self):
return u'Sheep'
And I pass animal_set to template and output every object like this {{ animal }}. It outputs Animal, but I created objects of sheep type and want to use __unicode__ method of sheep not of animal.
Do polymorphism work in Django models? I have found several answers, but there are snippets of code to write inside models, but I'm interested in native solutions.
At the time of writing, Django latest version was 1.2
But it needs some additional elements to work.
You need to assign a custom models.Manager object for each animal model which will call its own custom QuerySet object.
Basically, instead of returning Animal instances (this is what you get), SubclassingQuerySet calls as_leaf_class() method to check if item's model is Animal or not - if it is, then just return it, otherwise perform search in its model context. Thats it.
#models.py
from django.db import models
from django.contrib.contenttypes.models import ContentType
from django.db.models.query import QuerySet
class SubclassingQuerySet(QuerySet):
def __getitem__(self, k):
result = super(SubclassingQuerySet, self).__getitem__(k)
if isinstance(result, models.Model):
return result.as_leaf_class()
return result
def __iter__(self):
for item in super(SubclassingQuerySet, self).__iter__():
yield item.as_leaf_class()
class AnimalManager(models.Manager):
def get_query_set(self): # Use get_queryset for Django >= 1.6
return SubclassingQuerySet(self.model)
class Animal(models.Model):
name = models.CharField(max_length=100)
content_type = models.ForeignKey(ContentType, editable=False, null=True)
objects = AnimalManager()
def __unicode__(self):
return "Animal: %s" % (self.name)
def save(self, *args, **kwargs):
if not self.content_type:
self.content_type = ContentType.objects.get_for_model(self.__class__)
super(Animal, self).save(*args, **kwargs)
def as_leaf_class(self):
content_type = self.content_type
model = content_type.model_class()
if model == Animal:
return self
return model.objects.get(id=self.id)
class Sheep(Animal):
wool = models.IntegerField()
objects = AnimalManager()
def __unicode__(self):
return 'Sheep: %s' % (self.name)
Testing:
>>> from animals.models import *
>>> Animal.objects.all()
[<Sheep: Sheep: White sheep>, <Animal: Animal: Dog>]
>>> s, d = Animal.objects.all()
>>> str(s)
'Sheep: White sheep'
>>> str(d)
'Animal: Dog'
>>>
You might be successful by accessing {{ animal.sheep }} - the model inheritance is not what you would think, there is a heavy metaclass machinery under the cover that "converts" such inheritance into an implicit OneToOneField relationship.
There's a very simple django app called django-polymorphic-models that helps you with that. It will provide you with a downcast() method on the model itself that will return your "child" object, as well as a special queryset class to deal with these problems!
It can also be very useful to know that using select_related() on the base model's queryset will also get the child objects, that are referenced through a OneToOneField, which can be a nice performance boost sometimes!
I would recommend using Django proxy models, e.g. if you have the base model Animal which is subclassed by Sheep and Horse you would use:
class Animal(models.Model):
pass
class Horse(Animal):
class Meta(Animal.Meta):
proxy = True
class Sheep(Animal):
class Meta(Animal.Meta):
proxy = True
This is not what Proxy models are intended for but I wouldn't recommend using Django polymorphism unless you need the benefits of storing model specific data in separate tables. If you have a hundred horse specific attributes that all have default values stored in the database, and then only have 2 horse objects, but have a million sheep, you have a million rows, each with a hundred horse specific values you don't care about, but again this is only really relevant if you don't have enough disk space, which is unlikely. When polymorphism works well it's fine, but when it doesn't it's a pain.
You should check this answer: https://stackoverflow.com/a/929982/684253
The solution it proposes is similar to using django-polymorphic-models, that was already mentioned by #lazerscience. But I'd say django-model-utils is a little bit better documented than django-polymorphic, and the library is easier to use. Check the readme under "Inheritance Manager": https://github.com/carljm/django-model-utils/#readme
I am trying a simple custom manager, but I can't concatenate custom queries:
class MyManager(models.Manager):
def some_filter(self):
qs = self.get_query_set()
return qs.filter(score__gt = 10).order_by("-score")
class Game(models.Model):
score = models.IntegerField(blank=True, default=0)
objects = MyManager()
games = Game.objects.filter(any_filter).some_filter()[:5]
But I get QuerySet' object has no attribute 'some_filter'
Edit: It appears that the question is how to concatenate custom filter functions together: seomthing like games = Game.objects.some_filter1().some_filter2()[:5] just won't work for me.
You can apply some_filter() to MyManager object before QuerySet method filter()
games = Game.objects.some_filter().filter(any_filter)[:5]
Otherwise you should add some_filter method to QuerySet
I found a way to do it. A new QuerySet class need to be defined too
class GameQS(QuerySet):
def some_filter1(self):
return self.filter(score__gt = 10).order_by("-score")
def some_filter2(self):
return self.filter(score__gt = 50).order_by("-score")
class GameManager(models.Manager):
def get_query_set(self):
return GameQS(self.model, using=self._db)
def some_filer1(self):
return self.get_query_set().some_filter1()
def some_filter2(self):
return self.get_query_set().some_filter2()
If you are new in using model managers, first see GabiMe's answer
From django 1.7 onward, use queryset as manager class method to keep code DRY
MyQueryset.as_manager()
If you are using older verssions refer this question for more ways to optimize the code.
I'm trying to find a way to implement both a custom QuerySet and a custom Manager without breaking DRY. This is what I have so far:
class MyInquiryManager(models.Manager):
def for_user(self, user):
return self.get_query_set().filter(
Q(assigned_to_user=user) |
Q(assigned_to_group__in=user.groups.all())
)
class Inquiry(models.Model):
ts = models.DateTimeField(auto_now_add=True)
status = models.ForeignKey(InquiryStatus)
assigned_to_user = models.ForeignKey(User, blank=True, null=True)
assigned_to_group = models.ForeignKey(Group, blank=True, null=True)
objects = MyInquiryManager()
This works fine, until I do something like this:
inquiries = Inquiry.objects.filter(status=some_status)
my_inquiry_count = inquiries.for_user(request.user).count()
This promptly breaks everything because the QuerySet doesn't have the same methods as the Manager. I've tried creating a custom QuerySet class, and implementing it in MyInquiryManager, but I end up replicating all of my method definitions.
I also found this snippet which works, but I need to pass in the extra argument to for_user so it breaks down because it relies heavily on redefining get_query_set.
Is there a way to do this without redefining all of my methods in both the QuerySet and the Manager subclasses?
The Django 1.7 released a new and simple way to create combined queryset and model manager:
class InquiryQuerySet(models.QuerySet):
def for_user(self, user):
return self.filter(
Q(assigned_to_user=user) |
Q(assigned_to_group__in=user.groups.all())
)
class Inquiry(models.Model):
objects = InqueryQuerySet.as_manager()
See Creating Manager with QuerySet methods for more details.
Django has changed! Before using the code in this answer, which was written in 2009, be sure to check out the rest of the answers and the Django documentation to see if there is a more appropriate solution.
The way I've implemented this is by adding the actual get_active_for_account as a method of a custom QuerySet. Then, to make it work off the manager, you can simply trap the __getattr__ and return it accordingly
To make this pattern re-usable, I've extracted out the Manager bits to a separate model manager:
custom_queryset/models.py
from django.db import models
from django.db.models.query import QuerySet
class CustomQuerySetManager(models.Manager):
"""A re-usable Manager to access a custom QuerySet"""
def __getattr__(self, attr, *args):
try:
return getattr(self.__class__, attr, *args)
except AttributeError:
# don't delegate internal methods to the queryset
if attr.startswith('__') and attr.endswith('__'):
raise
return getattr(self.get_query_set(), attr, *args)
def get_query_set(self):
return self.model.QuerySet(self.model, using=self._db)
Once you've got that, on your models all you need to do is define a QuerySet as a custom inner class and set the manager to your custom manager:
your_app/models.py
from custom_queryset.models import CustomQuerySetManager
from django.db.models.query import QuerySet
class Inquiry(models.Model):
objects = CustomQuerySetManager()
class QuerySet(QuerySet):
def active_for_account(self, account, *args, **kwargs):
return self.filter(account=account, deleted=False, *args, **kwargs)
With this pattern, any of these will work:
>>> Inquiry.objects.active_for_account(user)
>>> Inquiry.objects.all().active_for_account(user)
>>> Inquiry.objects.filter(first_name='John').active_for_account(user)
UPD if you are using it with custom user(AbstractUser), you need to change
from
class CustomQuerySetManager(models.Manager):
to
from django.contrib.auth.models import UserManager
class CustomQuerySetManager(UserManager):
***
You can provide the methods on the manager and queryset using a mixin.
This also avoids the use of a __getattr__() approach.
from django.db.models.query import QuerySet
class PostMixin(object):
def by_author(self, user):
return self.filter(user=user)
def published(self):
return self.filter(published__lte=datetime.now())
class PostQuerySet(QuerySet, PostMixin):
pass
class PostManager(models.Manager, PostMixin):
def get_query_set(self):
return PostQuerySet(self.model, using=self._db)
You can now use the from_queryset() method on you manager to change its base Queryset.
This allows you to define your Queryset methods and your manager methods only once
from the docs
For advanced usage you might want both a custom Manager and a custom QuerySet. You can do that by calling Manager.from_queryset() which returns a subclass of your base Manager with a copy of the custom QuerySet methods:
class InqueryQueryset(models.Queryset):
def custom_method(self):
""" available on all default querysets"""
class BaseMyInquiryManager(models.Manager):
def for_user(self, user):
return self.get_query_set().filter(
Q(assigned_to_user=user) |
Q(assigned_to_group__in=user.groups.all())
)
MyInquiryManager = BaseInquiryManager.from_queryset(InquiryQueryset)
class Inquiry(models.Model):
ts = models.DateTimeField(auto_now_add=True)
status = models.ForeignKey(InquiryStatus)
assigned_to_user = models.ForeignKey(User, blank=True, null=True)
assigned_to_group = models.ForeignKey(Group, blank=True, null=True)
objects = MyInquiryManager()
A slightly improved version of T. Stone’s approach:
def objects_extra(mixin_class):
class MixinManager(models.Manager, mixin_class):
class MixinQuerySet(QuerySet, mixin_class):
pass
def get_query_set(self):
return self.MixinQuerySet(self.model, using=self._db)
return MixinManager()
Class decorators make usage as simple as:
class SomeModel(models.Model):
...
#objects_extra
class objects:
def filter_by_something_complex(self, whatever parameters):
return self.extra(...)
...
Update: support for nonstandard Manager and QuerySet base classes, e. g. #objects_extra(django.contrib.gis.db.models.GeoManager, django.contrib.gis.db.models.query.GeoQuerySet):
def objects_extra(Manager=django.db.models.Manager, QuerySet=django.db.models.query.QuerySet):
def oe_inner(Mixin, Manager=django.db.models.Manager, QuerySet=django.db.models.query.QuerySet):
class MixinManager(Manager, Mixin):
class MixinQuerySet(QuerySet, Mixin):
pass
def get_query_set(self):
return self.MixinQuerySet(self.model, using=self._db)
return MixinManager()
if issubclass(Manager, django.db.models.Manager):
return lambda Mixin: oe_inner(Mixin, Manager, QuerySet)
else:
return oe_inner(Mixin=Manager)
based on django 3.1.3 source code, i found a simple solution
from django.db.models.manager import BaseManager
class MyQuerySet(models.query.QuerySet):
def my_custom_query(self):
return self.filter(...)
class MyManager(BaseManager.from_queryset(MyQuerySet)):
...
class MyModel(models.Model):
objects = MyManager()
There are use-cases where we need to call custom QuerySet methods from the manager instead of using the get_manager method of a QuerySet.
A mixin would suffice based on the solution posted in one of the accepted solution comments.
class CustomQuerySetManagerMixin:
"""
Allow Manager which uses custom queryset to access queryset methods directly.
"""
def __getattr__(self, name):
# don't delegate internal methods to queryset
# NOTE: without this, Manager._copy_to_model will end up calling
# __getstate__ on the *queryset* which causes the qs (as `all()`)
# to evaluate itself as if it was being pickled (`len(self)`)
if name.startswith('__'):
raise AttributeError
return getattr(self.get_queryset(), name)
For example,
class BookQuerySet(models.QuerySet):
def published(self):
return self.filter(published=True)
def fiction(self):
return self.filter(genre="fiction")
def non_fiction(self):
return self.filter(genre="non-fiction")
class BookManager(CustomQuerySetManagerMixin, models.Manager):
def get_queryset(self):
return BookQuerySet(self.model, using=self._db).published()
class Book(models.Model):
title = models.CharField(max_length=200)
genre = models.CharField(choices=[('fiction', _('Fiction')), ('non-fiction', _('Non-Fiction'))])
published = models.BooleanField(default=False)
author = models.ForeignKey(Author, on_delete=models.CASCADE, related_name="books")
objects = BookManager()
class Author(models.Model):
name = models.CharField(max_length=200)
With the above, we can access related objects (Book) like below without defining new methods in the manager for each queryset method.
fiction_books = author.books.fiction()
The following works for me.
def get_active_for_account(self,account,*args,**kwargs):
"""Returns a queryset that is
Not deleted
For the specified account
"""
return self.filter(account = account,deleted=False,*args,**kwargs)
This is on the default manager; so I used to do something like:
Model.objects.get_active_for_account(account).filter()
But there is no reason it should not work for a secondary manager.