How do I get the object if it exists or None if it does not exist

Question

When I ask the model manager to get an object  it raises DoesNotExist when there is no matching object   go   Content objects get name  baby     Instead of DoesNotExist  how can I have go be None instead

User · Answer

Handling exceptions at different points in your views could really be cumbersome..What about defining a custom Model Manager, in the models.py file, like

class ContentManager(model.Manager):
    def get_nicely(self, **kwargs):
        try:
            return self.get(kwargs)
        except(KeyError, Content.DoesNotExist):
            return None

and then including it in the content Model class

class Content(model.Model):
    ...
    objects = ContentManager()

In this way it can be easily dealt in the views i.e.

post = Content.objects.get_nicely(pk = 1)
if post:
    # Do something
else:
    # This post doesn't exist

User · Answer

Maybe is better you use   User objects filter username admin username  exists

User · Answer

Since django 1 6 you can use first   method like so   Content objects filter name  baby   first

User · Answer

You can create a generic function for this  def get or none classmodel    kwargs       try          return classmodel objects get   kwargs      except classmodel DoesNotExist          return None  Use this like below  go   get or none Content name  quot baby quot    go will be None if no entry matches else will return the Content entry  Note It will raises exception MultipleObjectsReturned if more than one entry returned for name  quot baby quot   You should handle it on the data model to avoid this kind of error but you may prefer to log it at run time like this  def get or none classmodel    kwargs       try          return classmodel objects get   kwargs      except classmodel MultipleObjectsReturned as e          print  ERR     gt    e       except classmodel DoesNotExist          return None

User · Answer

From django docs     get   raises a DoesNotExist exception if an object is not found for the given parameters  This exception is also an attribute of the model class  The DoesNotExist  exception inherits from django core exceptions ObjectDoesNotExist   You can catch the exception and assign None to go   from django core exceptions import ObjectDoesNotExist try      go    Content objects get name  baby   except ObjectDoesNotExist      go   None

User · Answer

If you want a simple one-line solution that doesn t involve exception handling  conditional statements or a requirement of Django 1 6   do this instead   x   next iter SomeModel objects filter foo  bar     None

User · Answer

This is a copycat from Django s get object or 404 except that the method returns None  This is extremely useful when we have to use only   query to retreive certain fields only  This method can accept a model or a queryset   from django shortcuts import  get queryset   def get object or none klass   args    kwargs               Use get   to return an object  or return None if object     does not exist      klass may be a Model  Manager  or QuerySet object  All other passed     arguments and keyword arguments are used in the get   query      Like with QuerySet get    MultipleObjectsReturned is raised if more than     one object is found              queryset    get queryset klass      if not hasattr queryset   get            klass  name   klass   name   if isinstance klass  type  else klass   class     name           raise ValueError               First argument to get object or none   must be a Model  Manager                 or QuerySet  not   s      klass  name               try          return queryset get  args    kwargs      except queryset model DoesNotExist          return None

User · Answer

There is no  built in  way to do this  Django will raise the DoesNotExist exception every time  The idiomatic way to handle this in python is to wrap it in a try catch   try      go   SomeModel objects get foo  bar   except SomeModel DoesNotExist      go   None   What I did do  is to subclass models Manager  create a safe get like the code above and use that manager for my models  That way you can write  SomeModel objects safe get foo  bar

User · Answer

To make things easier  here is a snippet of the code I wrote  based on inputs from the wonderful replies here   class MyManager models Manager        def get or none self    kwargs           try              return self get   kwargs          except ObjectDoesNotExist              return None   And then in your model   class MyModel models Model       objects   MyManager     That s it  Now you have MyModel objects get   as well as MyModel objetcs get or none

User · Answer

You can do it this way   go    Content objects filter name  baby   first     Now go variable could be either the object you want or None  Ref  https   docs djangoproject com en 1 8 ref models querysets  django db models query QuerySet first

User · Answer

you could use exists with a filter   Content objects filter name  baby   exists    returns False or True depending on if there is anything in the QS   just an alternative for if you only want to know if it exists

User · Answer

I use Django 2 2 16  And this is how I solve this problem  from typing import Any  from django core exceptions import ObjectDoesNotExist from django db import models from django db models base import ModelBase from django db models manager import Manager   class SManager Manager       def get if exist self   args  Any    kwargs  Any           try              return self get  args    kwargs          except ObjectDoesNotExist              return None   class SModelBase ModelBase       def  prepare cls           manager   SManager           manager auto created   True         cls add to class  quot objects quot   manager           super    prepare        class Meta          abstract   True   class SModel models Model  metaclass SModelBase       managers   False      class Meta          abstract   True  And after that  in every models  you just need to import in  from custom models import SModel   class SUser SModel       pass  And in views  you can call like this  SUser objects get if exist id 1

User · Answer

It s one of those annoying functions that you might not want to re-implement   from annoying functions import get object or None      user   get object or None Content  name  baby

User · Answer

I think it isn t bad idea to use get object or 404    from django shortcuts import get object or 404  def my view request       my object   get object or 404 MyModel  pk 1    This example is equivalent to   from django http import Http404  def my view request       try          my object   MyModel objects get pk 1      except MyModel DoesNotExist          raise Http404  No MyModel matches the given query      You can read more about get object or 404   in django online documentation

User · Answer

Without exception   if SomeModel objects filter foo  bar   exists        x   SomeModel objects get foo  bar   else      x   None   Using an exception   try     x   SomeModel objects get foo  bar   except SomeModel DoesNotExist     x   None   There is a bit of an argument about when one should use an exception in python  On the one hand   it is easier to ask for forgiveness than for permission   While I agree with this  I believe that an exception should remain  well  the exception  and  the  ideal case  should run without hitting one

User · Answer

From django 1 7 onwards you can do like   class MyQuerySet models QuerySet        def get or none self    kwargs           try              return self get   kwargs          except self model DoesNotExist              return None   class MyBaseModel models Model        objects   MyQuerySet as manager     class MyModel MyBaseModel            class AnotherMyModel MyBaseModel             The advantage of  MyQuerySet as manager    is that both of the following will work   MyModel objects filter      get or none   MyModel objects get or none

User · Answer

We can use Django builtin exception which attached to the models named as  DoesNotExist  So  we don t have to import ObjectDoesNotExist exception   Instead doing    from django core exceptions import ObjectDoesNotExist  try      content   Content objects get name  baby   except ObjectDoesNotExist      content   None   We can do this   try      content   Content objects get name  baby   except Content DoesNotExist      content   None

User · Answer

I was facing with the same problem too  It s hard to write and read try-except for each time when you want to get an element from your model as in  Arthur Debert s answer  So  my solution is to create an Getter class which is inherited by the models  class Getter       classmethod     def try to get cls   args    kwargs           try              return cls objects get   kwargs          except Exception as e              return None  class MyActualModel models Model  Getter       pk id   models AutoField primary key True           In this way  I can get the actual element of MyActualModel or None  MyActualModel try to get pk id 1

User · Answer

Here s a variation on the helper function that allows you to optionally pass in a QuerySet instance  in case you want to get the unique object  if present  from a queryset other than the model s all objects queryset  e g  from a subset of child items belonging to a parent instance    def get unique or none model  queryset None    kwargs                   Performs the query on the specified  queryset           defaulting to the  all  queryset of the  model  s default manager          and returns the unique object matching the given         keyword arguments   Returns  None  if no match is found          Throws a  model MultipleObjectsReturned  exception         if more than one match is found              if queryset is None          queryset   model objects all       try          return queryset get   kwargs      except model DoesNotExist          return None   This can be used in two ways  e g     obj   get unique or none Model    kwargs  as previosuly discussed obj   get unique or none Model  parent children    kwargs

[python] How do I get the object if it exists, or None if it does not exist?

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