Based on your error message and [this other question][1], it seems to me this would fix it:

    p = Product.objects.filter(vendornumber=&#39;403516006&#39;)\
                   .order_by(&#39;vendor__name&#39;, &#39;-created&#39;).distinct(&#39;vendor__name&#39;)

That is, it seems that the `DISTINCT ON` expression(s) must match the leftmost `ORDER BY` expression(s). So by making the column you use in `distinct` as the first column in the `order_by`, I think it should work.

  [1]: https://stackoverflow.com/questions/9795660/postgresql-distinct-on-without-ordering

Just matching leftmost order_by() arg and distinct() did not work for me, producing the same error (Django 1.8.7 bug or a feature)?

    qs.order_by(&#39;project&#39;).distinct(&#39;project&#39;)

however it worked when I changed to:

    qs.order_by(&#39;project__id&#39;).distinct(&#39;project&#39;)

and I do not even have multiple order_by args.

In case you are hoping to use a separate field for distinct and order by another field you can use the below code
        

    from django.db.models import Subquery

    Model.objects.filter(
        pk__in=Subquery(
           Model.objects.all().distinct(&#39;foo&#39;).values(&#39;pk&#39;)
        )
    ).order_by(&#39;bar&#39;)



I had a similar issue but then with related fields. With just adding the related field in `distinct()`, I didn&#39;t get the right results.

I wanted to sort by `room__name` keeping the `person` (linked to `residency` ) unique. Repeating the related field as per the below fixed my issue:

    .order_by(&#39;room__name&#39;, &#39;residency__person&#39;, ).distinct(&#39;room__name&#39;, &#39;residency__person&#39;)

See also these related posts:
 
 - https://stackoverflow.com/questions/24865235/programmingerror-when-using-order-by-and-distinct-together-in-django
 - https://stackoverflow.com/questions/21621879/django-distinct-and-order-by
 - https://stackoverflow.com/questions/9795660/postgresql-distinct-on-with-different-order-by

I&#39;m using Visual Studio 2012 and have just installed [&quot;Microsoft ASP.NET and Web Frameworks 2013.1 - Visual Studio&quot;][1]. 

As expected, it added the option to create an `&quot;ASP.NET MVC 5 Empty Project&quot;`. The thing is, I see no way of jump-starting an [already functional &quot;base application&quot;][2] as I had when I was using MVC 4 (e.g. `&quot;Asp.NET MVC 4 Web Application&quot;`). I only see an empty template.

I&#39;ve seen answers such as:

- https://stackoverflow.com/questions/18288215/how-can-i-add-the-mvc-5-project-template-to-vs-2012

- https://stackoverflow.com/questions/17968304/create-and-run-mvc-5-project-in-vs-2012/19560412#19560412

- https://stackoverflow.com/questions/19608175/direct-download-link-to-asp-net-mvc-5-for-vs-2012?lq=1

And found [this article][3] on the matter.

This is obviously not a show-stopper as I can always create the application from a scratch, but I still would like to know if it is possible to achieve that on VS 2012. Did I miss a step, or do I need VS 2013 for that? A fully functional Web application template (with authentication etc.) would be nice to dabble around MVC 5&#39;s new features or for prototyping.


  [1]: http://blogs.msdn.com/b/webdev/archive/2013/11/18/announcing-release-of-asp-net-and-web-tools-2013-1-for-visual-studio-2012.aspx
  [2]: http://www.asp.net/mvc/tutorials/mvc-5/introduction/getting-started
  [3]: http://www.c-sharpcorner.com/UploadFile/4b0136/working-with-mvc-5-in-visual-studio-2012/

No ASP.NET MVC 5 Web Application Template on VS 2012?

If you look up how to clone an entire disk to another one on the web, you will find something like that:

    dd if=/dev/sda of=/dev/sdb conv=notrunc,noerror

While I understand the `noerror`, I am getting a hard time understanding why people think that `notrunc` is required for &quot;data integrity&quot; (as [ArchLinux&#39;s Wiki](https://wiki.archlinux.org/index.php/Disk_Cloning#Cloning_an_entire_hard_disk) states, for instance).

Indeed, I do agree on that if you are copying a partition to another partition on another disk, and you do not want to overwrite the entire disk, just one partition. In thise case `notrunc`, according to dd&#39;s manual page, is what you want.

But if you&#39;re cloning an entire disk, what does `notrunc` change for you? Just time optimization?




Why using conv=notrunc when cloning a disk with dd?

How can I make an `order_by` like this ....

    p = Product.objects.filter(vendornumber=&#39;403516006&#39;)\
                       .order_by(&#39;-created&#39;).distinct(&#39;vendor__name&#39;)

The problem is that I have multiple vendors with the same name, and I only want the latest product by the vendor ..

Hope it makes sense?

I got this DB error:

&gt; SELECT DISTINCT ON expressions must match initial ORDER BY expressions
&gt; LINE 1: SELECT DISTINCT ON (&quot;search_vendor&quot;.&quot;name&quot;)
&gt; &quot;search_product&quot;...

Django order_by() filter with distinct()

How can I make an <code>order_by</code> like this ....
<pre><code class="hljs language-less">p = Product.objects.filter(vendornumber='403516006')\
 .order_by('-created').distinct('vendor__name')
</code></pre>
The problem is that I have multiple vendors with the same name, and I only want the latest product by the vendor ..
Hope it makes sense?
I got this DB error:
> SELECT DISTINCT ON expressions must match initial ORDER BY expressions
> LINE 1: SELECT DISTINCT ON ("search_vendor"."name")
> "search_product"...

I&#39;m trying to return a HttpResponse from Django Rest Framework including data from 2 linked models.
The models are:

    class Wine(models.Model):
    
    	color = models.CharField(max_length=100, blank=True)
    	country = models.CharField(max_length=100, blank=True)
    	region = models.CharField(max_length=100, blank=True)
    	appellation = models.CharField(max_length=100, blank=True)

    class Bottle(models.Model):
    
    	wine = models.ForeignKey(Wine, null=False)
    	user = models.ForeignKey(User, null=False, related_name=&#39;bottles&#39;)

I&#39;d like to have a serializer for the Bottle model which includes information from the related Wine.

I tried:

    class BottleSerializer(serializers.HyperlinkedModelSerializer):
    	wine = serializers.RelatedField(source=&#39;wine&#39;)
    
    	class Meta:
    		model = Bottle
    		fields = (&#39;url&#39;, &#39;wine.color&#39;, &#39;wine.country&#39;, &#39;user&#39;, &#39;date_rated&#39;, &#39;rating&#39;, &#39;comment&#39;, &#39;get_more&#39;)

which doesn&#39;t work.

Any ideas how I could do that?

Thanks :)

Django Rest Framework - Get related model field in serializer

I want to use Intellij Idea within my existing python django project which was built within a virtual environment in ubuntu. How do I configure Intellij Idea to use the libraries of the virtual environment?

Using IntellijIdea within an existing virtualenv

I&#39;m really having a difficult time grasping the concept of Django&#39;s content types. It feels very hackish and, ultimately, against how Python tends to do things.  That being said, if I&#39;m going to use Django then I have to work within the confines of the framework.

So I&#39;m coming here wondering if anyone can give a practical real world example of how a content type works and how you would implement it. Almost all the tutorials (mostly on blogs) I have reviewed don&#39;t do a great job really covering the concept. They seem to pick up where the Django documentation left off (what seems like nowhere).

How exactly do Django content types work?

I&#39;m a django beginner so I&#39;m trying to understand the concept of context and context processor.

- What is a context and why do you use it? 
- Is a context a value you need to have available in order to use in a template?
- Is a context and a context processor the same?

I&#39;ll apreciate a lot your response. Thanks in advance!

What is a context in Django?

I have a django (1.6.x) project that runs fine with the dev server, but is failing under Apache2 (2.2.22.1) and mod_wsgi (3.3-4) on Ubuntu 12.04.3 with the error

ImproperlyConfigured: The included urlconf erp.urls doesn&#39;t have any patterns in it

I don&#39;t understand why it would work with the dev server but not Apache2/mod_wsgi and I&#39;m finding it difficult to track down where the error is coming from.

There are a number of other SO questions similar, but the only place I use reverse (one problem previously found) is in get_absolute_url in my models - this should be fine?


The project is set up a la Two Scoops style, in particular the layout is:

`&lt;repository_root&gt;/&lt;django_project_root&gt;/&lt;configuration_root&gt;/`

which translates to:

`erp_root/erp/erp/`

and the settings are

`erp_root/erp/erp/settings/*py` (including the `__init__.py`)


erp/urls.py;

    from django.conf import settings
    from django.conf.urls import patterns, include, url
    from django.contrib import admin
    admin.autodiscover()

    urlpatterns = patterns(&#39;&#39;,
        url(r&#39;^$&#39;, &#39;django.contrib.auth.views.login&#39;, {&#39;template_name&#39;: &#39;login.html&#39;}),
        url(r&#39;^admin/&#39;, include(admin.site.urls)),
        url(r&#39;^login/$&#39;, &#39;django.contrib.auth.views.login&#39;, {&#39;template_name&#39;: &#39;login.html&#39;}, name=&#39;login&#39;),
        url(r&#39;^logout/$&#39;, &#39;django.contrib.auth.views.logout_then_login&#39;, {}, name=&#39;logout&#39;),
        url(r&#39;^search/&#39;, include(&#39;haystack.urls&#39;)),
        url(r&#39;^inventory/&#39;, include(&#39;inventory.urls&#39;)),
    )

    if settings.DEBUG:
        import debug_toolbar
        urlpatterns += patterns(&#39;&#39;,
        url(r&#39;^__debug__/&#39;, include(debug_toolbar.urls)),
    )



and inventory/urls.py:

    from django.conf.urls import url, patterns
    from .forms import CarrierWizardForm1, CarrierWizardForm2, MovementWizardForm1,MovementWizardForm2
    from . import views

    carrier_wizard_forms = [CarrierWizardForm1, CarrierWizardForm2]
    movement_wizard_forms = [MovementWizardForm1, MovementWizardForm2]

    urlpatterns = patterns(&#39;&#39;,
        url(r&#39;^$&#39;, views.PartNumberListView.as_view(), name=&#39;inventory_list_index&#39;),
        url(r&#39;^parttype/$&#39;, views.part_type_list, name=&#39;index&#39;),
        url(r&#39;^parttype/(?P&lt;parttype&gt;\d{2})/$&#39;, views.part_type_view, name=&#39;part_type_view&#39;),
        url(r&#39;^partnumber/$&#39;, views.PartNumberListView.as_view(), name=&#39;partnumber_list&#39;),
        url(r&#39;^partnumber/add/$&#39;, views.PartNumberCreateView.as_view(), name=&#39;partnumber_add&#39;),
        url(r&#39;^partnumber/(?P&lt;slug&gt;[-\w]+)/$&#39;, views.PartNumberView.as_view(), name=&#39;partnumber_view&#39;),
        url(r&#39;^partnumber/(?P&lt;slug&gt;[-\w]+)/update/$&#39;, views.PartNumberUpdateView.as_view(), name=&#39;partnumber_update&#39;),
        url(r&#39;^partnumber/(?P&lt;slug&gt;[-\w]+)/delete/$&#39;, views.PartNumberDeleteView.as_view(), name=&#39;partnumber_delete&#39;),
        ....
           )

and erp/settings/dev.py:

    # Django settings for erp project.
    # settings.py
    
    from unipath import Path
    
    PROJECT_DIR = Path(__file__).ancestor(3)
    MEDIA_ROOT = PROJECT_DIR.child(&quot;media&quot;)
    STATIC_ROOT = PROJECT_DIR.child(&quot;static&quot;)
    STATICFILES_DIRS = (
      PROJECT_DIR.child(&quot;assets&quot;),
    )
    TEMPLATE_DIRS = (
      PROJECT_DIR.child(&quot;templates&quot;),
    )
    
    
    DEBUG = True
    TEMPLATE_DEBUG = DEBUG
    
    TIME_ZONE = &#39;Australia/Melbourne&#39;
    LANGUAGE_CODE = &#39;en-au&#39;
    SITE_ID = 1
    USE_TZ = True
    
    DATE_FORMAT = &#39;d/m/y&#39;
    SHORT_DATE_FORMAT = &#39;d/m/y&#39;
    
    # URL that handles the media served from MEDIA_ROOT. Make sure to use a
    # trailing slash.
    # Examples: &quot;http://example.com/media/&quot;, &quot;http://media.example.com/&quot;
    MEDIA_URL = &#39;&#39;
    
    # Absolute path to the directory static files should be collected to.
    # Don&#39;t put anything in this directory yourself; store your static files
    # in apps&#39; &quot;static/&quot; subdirectories and in STATICFILES_DIRS.
    # Example: &quot;/var/www/example.com/static/&quot;
    STATIC_ROOT = &#39;&#39;
    
    # URL prefix for static files.
    # Example: &quot;http://example.com/static/&quot;, &quot;http://static.example.com/&quot;
    STATIC_URL = &#39;/static/&#39;
    
    STATICFILES_FINDERS = (
        &#39;django.contrib.staticfiles.finders.FileSystemFinder&#39;,
        &#39;django.contrib.staticfiles.finders.AppDirectoriesFinder&#39;,
    )
    
    # List of callables that know how to import templates from various sources.
    TEMPLATE_LOADERS = (
        &#39;django.template.loaders.filesystem.Loader&#39;,
        &#39;django.template.loaders.app_directories.Loader&#39;,
    )
    
    MIDDLEWARE_CLASSES = (
        &#39;debug_toolbar.middleware.DebugToolbarMiddleware&#39;,
        &#39;django.middleware.common.CommonMiddleware&#39;,
        &#39;django.contrib.sessions.middleware.SessionMiddleware&#39;,
        &#39;django.middleware.csrf.CsrfViewMiddleware&#39;,
        &#39;django.contrib.auth.middleware.AuthenticationMiddleware&#39;,
        &#39;django.contrib.messages.middleware.MessageMiddleware&#39;,
        &#39;stronghold.middleware.LoginRequiredMiddleware&#39;,
        &#39;django.middleware.clickjacking.XFrameOptionsMiddleware&#39;,
    )
    
    ROOT_URLCONF = &#39;erp.urls&#39;

    # Python dotted path to the WSGI application used by Django&#39;s runserver.
    WSGI_APPLICATION = &#39;erp.wsgi.application&#39;

    
    INSTALLED_APPS = (
        &#39;django.contrib.auth&#39;,
        &#39;django.contrib.contenttypes&#39;,
        &#39;django.contrib.sessions&#39;,
        &#39;django.contrib.sites&#39;,
        &#39;django.contrib.messages&#39;,
        &#39;django.contrib.staticfiles&#39;,
        &#39;django.contrib.admin&#39;,
        &#39;django.contrib.formtools&#39;,
        &#39;django.contrib.humanize&#39;,
        &#39;inventory&#39;,
        &#39;django_extensions&#39;,
        &#39;extra_views&#39;,
        &#39;debug_toolbar&#39;,
        &#39;django_tables2&#39;,
        &#39;stronghold&#39;,
        &#39;bootstrap3&#39;,
        &#39;haystack&#39;,
    )

    LOGIN_URL = &#39;/login&#39;
    LOGOUT_URL = &#39;/logout&#39;
    
    # For Stronghold
    STRONGHOLD_PUBLIC_NAMED_URLS = (
        &#39;login&#39;,
        &#39;logout&#39;,
    )

    # This is required by the debug toolbar middleware
    INTERNAL_IPS = (&#39;192.168.0.16&#39;,&#39;0.0.0.0&#39;,&#39;127.0.0.1&#39;,&#39;::1&#39;, &#39;192.168.0.115&#39;)

    # This is reqquired by django_tables2
    TEMPLATE_CONTEXT_PROCESSORS = (&quot;django.contrib.auth.context_processors.auth&quot;,
                               &quot;django.core.context_processors.debug&quot;,
                               &quot;django.core.context_processors.i18n&quot;,
                               &quot;django.core.context_processors.media&quot;,
                               &quot;django.core.context_processors.static&quot;,
                               &quot;django.core.context_processors.tz&quot;,
                               &quot;django.contrib.messages.context_processors.messages&quot;,
                               &quot;django.core.context_processors.request&quot;
                              )
    }
    
    LOGIN_REDIRECT_URL = &#39;/inventory/&#39;
    
    DEBUG_TOOLBAR_PANELS = [
    &#39;debug_toolbar.panels.versions.VersionsPanel&#39;,
    &#39;debug_toolbar.panels.timer.TimerPanel&#39;,
    &#39;debug_toolbar.panels.settings.SettingsPanel&#39;,
    &#39;debug_toolbar.panels.headers.HeadersPanel&#39;,
    &#39;debug_toolbar.panels.request.RequestPanel&#39;,
    &#39;debug_toolbar.panels.sql.SQLPanel&#39;,
    &#39;debug_toolbar.panels.staticfiles.StaticFilesPanel&#39;,
    &#39;debug_toolbar.panels.templates.TemplatesPanel&#39;,
    &#39;debug_toolbar.panels.cache.CachePanel&#39;,
    &#39;debug_toolbar.panels.signals.SignalsPanel&#39;,
    &#39;debug_toolbar.panels.logging.LoggingPanel&#39;,
    ]

    def show_toolbar(request):
        return True  # Always show toolbar, for example purposes only.

    DEBUG_TOOLBAR_CONFIG = {
    &#39;INTERCEPT_REDIRECTS&#39;: False,
    &#39;INSERT_BEFORE&#39;: &#39;&lt;/body&gt;&#39;,
    &#39;ENABLE_STACKTRACES&#39;: True,
    }

    # This is required for Haystack - the search engine
    HAYSTACK_CONNECTIONS = {
          &#39;default&#39;: {
        &#39;ENGINE&#39;: &#39;haystack.backends.solr_backend.SolrEngine&#39;,
        &#39;URL&#39;: &#39;http://127.0.0.1:8085/solr/erp&#39;,
      },
    }

My wsgi is the standard with minor settings mod:

    import os
    os.environ.setdefault(&quot;DJANGO_SETTINGS_MODULE&quot;, &quot;erp.settings.settings&quot;)
    from django.core.wsgi import get_wsgi_application
    application = get_wsgi_application()

My apache2/sites-avail/erp.conf is:

    &lt;VirtualHost *:80&gt;
       ServerName deverp
       ServerAdmin administrator
       DocumentRoot /path/www/dev/erp/erp/
       ErrorLog /var/log/apache2/dev/error.log
       CustomLog /var/log/apache2/dev/access.log combined
       WSGIDaemonProcess deverp python-path=/path/www/dev/erp/erp:/path/.virtualenvs/erp-dev/lib/python2.7/site-packages
       WSGIProcessGroup deverp
       WSGIScriptAlias / /path/www/dev/erp/erp/erp/wsgi.py
      &lt;Directory /path/www/dev/erp/erp/erp&gt;
      &lt;Files wsgi.py&gt;
        Order deny,allow
        Allow from all
      &lt;/Files&gt;
      &lt;/Directory&gt;
    &lt;/VirtualHost&gt;



ImproperlyConfigured: The included urlconf &lt;project&gt;.urls doesn&#39;t have any patterns in it

I am making an `Order` model for a shopping cart and I need to make a field that auto increments when the order is made:

    class Order(models.Model):
        cart = models.ForeignKey(Cart)
        add_date = models.DateTimeField(auto_now_add=True)
        order_number = models.IntegerField()
        enable = models.BooleanField(default=True)

How do I make the `IntegerField` auto increment?

How do I make an auto increment integer field in Django?

How does one convert a django Model object to a dict with **all** of its fields?  All ideally includes foreign keys and fields with editable=False.

Let me elaborate.  Let&#39;s say I have a django model like the following:

    from django.db import models

    class OtherModel(models.Model): pass

    class SomeModel(models.Model):
        normal_value = models.IntegerField()
        readonly_value = models.IntegerField(editable=False)
        auto_now_add = models.DateTimeField(auto_now_add=True)
        foreign_key = models.ForeignKey(OtherModel, related_name=&quot;ref1&quot;)
        many_to_many = models.ManyToManyField(OtherModel, related_name=&quot;ref2&quot;)

In the terminal, I have done the following:

    other_model = OtherModel()
    other_model.save()
    instance = SomeModel()
    instance.normal_value = 1
    instance.readonly_value = 2
    instance.foreign_key = other_model
    instance.save()
    instance.many_to_many.add(other_model)
    instance.save()

I want to convert this to the following dictionary:

    {&#39;auto_now_add&#39;: datetime.datetime(2015, 3, 16, 21, 34, 14, 926738, tzinfo=&lt;UTC&gt;),
     &#39;foreign_key&#39;: 1,
     &#39;id&#39;: 1,
     &#39;many_to_many&#39;: [1],
     &#39;normal_value&#39;: 1,
     &#39;readonly_value&#39;: 2}

----------
Questions with unsatisfactory answers:

https://stackoverflow.com/questions/1123337/django-converting-an-entire-set-of-a-models-objects-into-a-single-dictionary

https://stackoverflow.com/questions/12382546/how-can-i-turn-django-model-objects-into-a-dictionary-and-still-have-their-forei

Convert Django Model object to dict with all of the fields intact

When I tried to relate an attribute with another one which has an **M to M** relation I received this error:

&gt; get() returned more than one topic -- it returned 2!

Can you guys tell me what that means and maybe tell me in advance how to avoid this error ?

**models**

    class LearningObjective(models.Model):
        learning_objective=models.TextField()

    class Topic(models.Model):
        learning_objective_topic=models.ManyToManyField(LearningObjective)
        topic=models.TextField()


output of `LearningObjective.objects.all()`

    [&lt;LearningObjective: lO1&gt;, &lt;LearningObjective: lO2&gt;, &lt;LearningObjective: lO3&gt;]

output of `Topic.objects.all()`

    [&lt;Topic: Topic object&gt;, &lt;Topic: Topic object&gt;, &lt;Topic: Topic object&gt;, &lt;Topic: Topic object&gt;, &lt;Topic: Topic object&gt;, &lt;Topic: Topic object&gt;, &lt;Topic: Topic object&gt;, &lt;Topic: Topic object&gt;, &lt;Topic: Topic object&gt;, &lt;Topic: Topic object&gt;, &lt;Topic: Topic object&gt;, &lt;Topic: Topic object&gt;, &lt;Topic: Topic object&gt;, &lt;Topic: Topic object&gt;]

**views**
   
     def create_themen(request):
         new_topic=Topic(topic=request.POST[&#39;topic&#39;])
         new_topic.save()
         return render(request, &#39;topic.html&#39;, {&#39;topic&#39;: topic.objects.all()})
     
     def create_learning_objective(request):
         new_learning_objective=LearningObjective(learning_objective=request.POST[&#39;learning_objective&#39;])
         new_learning_objective.save()
         new_learning_objective_topic=Topic.objects.get(topic=request.POST[&#39;topic&#39;])
         new_learning_objective_topic.new_learning_objective_topic.add(new_learning_objective)
         return render( request, &#39;learning_objective.html&#39;, {
                        &#39;topic&#39;: Topic.objects.all(),
                        &#39;todo&#39;: TodoList.objects.all(),
                        &#39;learning_objective&#39;: LearningObjective.objects.all()
                      })

django - get() returned more than one topic

How do i get a list of all id/primary key for a table. Say i have this table:

        
    class Blog(models.Model)
      title = models.CharField()
      body = models.CharField()
      author = models.ForeignKey(Author)

assume the field *author* is an Author object. I want to get all the ids of Blog where author=author

i know i can use      
        
        blogs = Blog.objects.filter(author=author)

and get all the blog objects in a list form, but how do i get the list IDS/PK? Similar to &quot;Select id from Blog where Author=author&quot;



django models: get list of id

Given a Django model with a [JSONField][1], what is the correct way of serializing and deserializing it using [Django Rest Framework][2]?

I&#39;ve already tried crating a custom `serializers.WritableField` and overriding `to_native` and `from_native`:

    from json_field.fields import JSONEncoder, JSONDecoder
    from rest_framework import serializers

    class JSONFieldSerializer(serializers.WritableField):
        def to_native(self, obj):
        return json.dumps(obj, cls = JSONEncoder)
    	
        def from_native(self, data):
            return json.loads(data, cls = JSONDecoder)


But when I try to updating the model using `partial=True`, all the floats in the JSONField objects become strings.

  [1]: https://github.com/bradjasper/django-jsonfield
  [2]: http://www.django-rest-framework.org/

Django Rest Framework and JSONField

Consider simple Django models `Event` and `Participant`:

    class Event(models.Model):
        title = models.CharField(max_length=100)
    
    class Participant(models.Model):
        event = models.ForeignKey(Event, db_index=True)
        is_paid = models.BooleanField(default=False, db_index=True)
    
It&#39;s easy to annotate events query with total number of participants:

    events = Event.objects.all().annotate(participants=models.Count(&#39;participant&#39;))

**How to annotate with count of participants filtered by `is_paid=True`?**

I need to query **all events** regardless of number of participants, e.g. I don&#39;t need to filter by annotated result. If there are `0` participants, that&#39;s ok, I just need `0` in annotated value.

The [example from documentation](https://docs.djangoproject.com/en/1.8/topics/db/aggregation/#order-of-annotate-and-filter-clauses) doesn&#39;t work here, because it excludes objects from query instead of annotating them with `0`.

**Update.** Django 1.8 has new [conditional expressions feature](https://docs.djangoproject.com/en/1.8/ref/models/conditional-expressions/), so now we can do like this:

    events = Event.objects.all().annotate(paid_participants=models.Sum(
        models.Case(
            models.When(participant__is_paid=True, then=1),
            default=0,
            output_field=models.IntegerField()
        )))


**Update 2.** Django 2.0 has new [Conditional aggregation](https://docs.djangoproject.com/en/2.0/ref/models/conditional-expressions/#conditional-aggregation) feature, see [the accepted answer](https://stackoverflow.com/a/48649024/326406) below.

**Update 3.** For Django 3.x please [check this answer below](https://stackoverflow.com/a/70234015/326406).

How to filter objects for count annotation in Django?

This is a bleeding-edge feature that I&#39;m currently skewered upon and quickly bleeding out. I want to annotate a subquery-aggregate onto an existing queryset. Doing this before 1.11 either meant custom SQL or hammering the database. [Here&#39;s the documentation for this][1], and the example from it:

    from django.db.models import OuterRef, Subquery, Sum
    comments = Comment.objects.filter(post=OuterRef(&#39;pk&#39;)).values(&#39;post&#39;)
    total_comments = comments.annotate(total=Sum(&#39;length&#39;)).values(&#39;total&#39;)
    Post.objects.filter(length__gt=Subquery(total_comments))

They&#39;re *annotating* on the aggregate, which seems weird to me, but whatever.

I&#39;m struggling with this so I&#39;m boiling it right back to the simplest real-world example I have data for. I have `Carpark`s which contain many `Space`s. Use `Book→Author` if that makes you happier but —for now— I just want to annotate on a count of the related model using `Subquery`\*.

    spaces = Space.objects.filter(carpark=OuterRef(&#39;pk&#39;)).values(&#39;carpark&#39;)
    count_spaces = spaces.annotate(c=Count(&#39;*&#39;)).values(&#39;c&#39;)
    Carpark.objects.annotate(space_count=Subquery(count_spaces))

This gives me a lovely `ProgrammingError: more than one row returned by a subquery used as an expression` and in my head, this error makes perfect sense. The subquery is returning a list of spaces with the annotated-on total.

The example suggested that some sort of magic would happen and I&#39;d end up with a number I could use. But that&#39;s not happening here? How do I annotate on aggregate Subquery data?

## Hmm, something&#39;s being added to my query&#39;s SQL...

I built a new Carpark/Space model and it worked. So the next step is working out what&#39;s poisoning my SQL. On Laurent&#39;s advice, I took a look at the SQL and tried to make it more like the version they posted in their answer. And this is where I found the real problem:

&lt;pre&gt;&lt;code&gt;SELECT &quot;bookings_carpark&quot;.*, (SELECT COUNT(U0.&quot;id&quot;) AS &quot;c&quot;
FROM &quot;bookings_space&quot; U0
WHERE U0.&quot;carpark_id&quot; = (&quot;bookings_carpark&quot;.&quot;id&quot;)
GROUP BY U0.&quot;carpark_id&quot;&lt;strong&gt;, U0.&quot;space&quot;&lt;/strong&gt;
)
AS &quot;space_count&quot; FROM &quot;bookings_carpark&quot;;&lt;/code&gt;&lt;/pre&gt;

I&#39;ve highlighted it but it&#39;s that subquery&#39;s `GROUP BY ... U0.&quot;space&quot;`. It&#39;s retuning both for some reason. Investigations continue.

Edit 2: Okay, just looking at the subquery SQL I can see that second group by coming through ☹

    In [12]: print(Space.objects_standard.filter().values(&#39;carpark&#39;).annotate(c=Count(&#39;*&#39;)).values(&#39;c&#39;).query)
    SELECT COUNT(*) AS &quot;c&quot; FROM &quot;bookings_space&quot; GROUP BY &quot;bookings_space&quot;.&quot;carpark_id&quot;, &quot;bookings_space&quot;.&quot;space&quot; ORDER BY &quot;bookings_space&quot;.&quot;carpark_id&quot; ASC, &quot;bookings_space&quot;.&quot;space&quot; ASC

**Edit 3**: Okay! Both these models have sort orders. These are being carried through to the subquery. It&#39;s these orders that are bloating out my query and breaking it.

I guess this might be a bug in Django but short of removing the Meta-order_by on both these models, **is there any way I can *unsort* a query at querytime?**

---

&lt;sub&gt;\***I know I could just annotate a Count for this example**. My real purpose for using this is a much more complex filter-count but I can&#39;t even get this working.&lt;/sub&gt;


  [1]: https://docs.djangoproject.com/en/1.11/ref/models/expressions/#using-aggregates-within-a-subquery-expression

Content Type	Original Author	Original Content on Stackoverflow
Question	pkdkk	View Question on Stackoverflow
Solution 1 - Django	janos	View Answer on Stackoverflow
Solution 2 - Django	Dmitriy Sintsov	View Answer on Stackoverflow
Solution 3 - Django	kophygiddie	View Answer on Stackoverflow
Solution 4 - Django	SaeX	View Answer on Stackoverflow

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