Try this:

    Rating.objects.filter(attribute__in=attributes) \
        .values(&#39;location&#39;) \
        .annotate(score = Sum(&#39;score&#39;)) \
        .order_by(&#39;-score&#39;)

Can you try this.

    Rating.objects.values(&#39;location_id&#39;).filter(attribute__in=attributes).annotate(sum_score=Sum(&#39;score&#39;)).order_by(&#39;-score&#39;)

In this period I am studing the Spring MVC showcase example (downloadable from STS dasboard) and I have some simple question about the `Request Mapping` examples:

1) In my `home.jsp` page I have this link:

			&lt;li&gt;
				&lt;a id=&quot;byParameter&quot; class=&quot;textLink&quot; href=&quot;&lt;c:url value=&quot;/mapping/parameter?foo=bar&quot; /&gt;&quot;&gt;By path, method, and presence of parameter&lt;/a&gt;
			&lt;/li&gt;

As you can see by this link I am doing an HTTP GET Request having a &quot;foo&quot; parameter containing the value: &quot;bar&quot;.

This HTTP Request is handled by the following method of the controller class MappingController:

	@RequestMapping(value=&quot;/mapping/parameter&quot;, method=RequestMethod.GET, params=&quot;foo&quot;)
	public @ResponseBody String byParameter() {
		return &quot;Mapped by path + method + presence of query parameter! (MappingController)&quot;;
	}

This method manage HTTP Request (only `GET` type) that have a parameter named &quot;foo&quot;

How can I take the value (&quot;bar&quot;) of this parameter and put it in a variable inside the code of my by Parameter method?

Spring MVC How take the parameter value of a GET HTTP Request in my controller method?

When people are comparing SQL and noSQL, and concluding the upsides and downsides of each one, what I never hear anyone talking about is the speed. 

Isn&#39;t performing SQL queries generally **faster** than performing noSQL queries? 

I mean, for me this would be a really obvious conclusion, because you should always be able to find something faster if you **know** the structure of your database than if you don&#39;t.

But people never seem to mention this, so I want to know if my conclusion is right or wrong.

SQL versus noSQL (speed)

I have a fairly simple query I&#39;d like to make via the ORM, but can&#39;t figure that out..

I have three models:

Location (a place), Attribute (an attribute a place might have), and Rating (a M2M &#39;through&#39; model that also contains a score field)

I want to pick some important attributes and be able to rank my locations by those attributes - i.e. higher total score over all selected attributes = better.

I can use the following SQL to get what I want:

    select location_id, sum(score) 
        from locations_rating 
        where attribute_id in (1,2,3) 
        group by location_id order by sum desc;

which returns

     location_id | sum 
    -------------+-----
              21 |  12
               3 |  11

The closest I can get with the ORM is:

    Rating.objects.filter(
        attribute__in=attributes).annotate(
        acount=Count(&#39;location&#39;)).aggregate(Sum(&#39;score&#39;))

Which returns 

    {&#39;score__sum&#39;: 23}

i.e. the sum of all, not grouped by location.

Any way around this? I could execute the SQL manually, but would rather go via the ORM to keep things consistent.

Thanks

How to group by AND aggregate with Django

I have a fairly simple query I'd like to make via the ORM, but can't figure that out..
I have three models:
Location (a place), Attribute (an attribute a place might have), and Rating (a M2M 'through' model that also contains a score field)
I want to pick some important attributes and be able to rank my locations by those attributes - i.e. higher total score over all selected attributes = better.
I can use the following SQL to get what I want:
<pre><code class="hljs language-csharp">select location_id, sum(score) 
 from locations_rating 
 where attribute_id in (1,2,3) 
 group by location_id order by sum desc;
</code></pre>
which returns
<pre><code class="hljs language-bash"> location_id | sum 
-------------+-----
 21 | 12
 3 | 11
</code></pre>
The closest I can get with the ORM is:
<pre><code class="hljs language-ini">Rating.objects.filter(
 attribute__in=attributes).annotate(
 acount=Count('location')).aggregate(Sum('score'))
</code></pre>
Which returns
<pre><code class="hljs language-arduino">{'score__sum': 23}
</code></pre>
i.e. the sum of all, not grouped by location.
Any way around this? I could execute the SQL manually, but would rather go via the ORM to keep things consistent.
Thanks

I have a Postgres schema which looks like:

![enter image description here][1]

The problem is that whenever I save text longer than 500 characters in the description column I get the error:

    value too long for type character varying(500)

In the documentation for Postgres it says type text can have unlimited characters.

I&#39;m using postgresql-9.1.

This table has been generated using Django 1.4 and the field type in the model is TextField, if that helps explain the problem further.

Any ideas as why this is happening and what I can do to fix it?

  [1]: http://i.stack.imgur.com/wQ4l0.png

Strange PostgreSQL &quot;value too long for type character varying(500)&quot;

I have to generate a FormSet from a model but I need to insert an &quot;extra value&quot; in to every form.

Specifically, I have a JApplet that generates some Markers and Paths on a image, and POST it on the server.

In my model lines are composed from two Markers. But when I POST it, because I&#39;m using the id generated from the JApplet and not from the database, I will not know from which Markers a Path will be composed.

So I thought to insert a &quot;temporary id&quot; on the Marker on the form, and do the correct arrangements in the view before saving the Path.

I thought about defining a custom form for the markers, but it not seems to be very DRY, and I don&#39;t want to came back to this if I change the Marker model.

Here is the form:

      class PointForm(forms.ModelForm):
        temp_id = forms.IntegerField()
        class Meta:
                model = Point
                
        def clean(self):
                if any(self.errors):
                        # Don&#39;t bother validating the formset unless each form is valid on its own
                        return
      
                ingresso = self.cleaned_data[&#39;ingresso&#39;]
                ascensore = self.cleaned_data[&#39;ascensore&#39;]
                scala = self.cleaned_data[&#39;scala&#39;]
                
                if (ingresso and ascensore) or (ingresso and scala) or (ascensore and scala):
                        raise forms.ValidationError(&quot;A stair cannot be a elevator or an access!!!&quot;) 
                return self
        
        def save(commit=True):
        # do something with self.cleaned_data[&#39;temp_id&#39;]
                super(PointForm).save(commit=commit)
         

And the model:

      class Point(models.Model):

        RFID = models.CharField(max_length=200, blank=True)
        
        x = models.IntegerField()
        y = models.IntegerField()
        
        piano = models.ForeignKey(Floor)
        
        ingresso = models.BooleanField()

The error:


      ViewDoesNotExist at /admin/
      Could not import buildings.views.getFloors. View does not exist in module buildings.views.
      Request Method:	GET
      Request URL:	http://127.0.0.1:8000/admin/
      Django Version:	1.4.1
      Exception Type:	ViewDoesNotExist
      Exception Value:	
      Could not import buildings.views.getFloors. View does not exist in module buildings.views.
      Exception Location:	/usr/local/lib/python2.7/dist-packages/django/core/urlresolvers.py in get_callable, line 101


The error is generated when I try to load the admin page, this page has no references at all with the form. 


**SOLUTION FOR EXCEPTION**

Ok, I&#39;ll write here how to find out why Django was doing such a strange thing.

[Here][1] it&#39;s a correct way to find out what is the problem. 

The exception was thrown because I forgot to add `forms.py` to the `from django import forms`.




  [1]: https://stackoverflow.com/questions/11393257/viewdoesnotexist-error

Django add extra field to a ModelForm generated from a Model

I want to edit a `django-rest-framwork` serializer object before it is saved. This is how I currently do it -   

    def upload(request):
        if request.method == &#39;POST&#39;:
            form = ImageForm(request.POST, request.FILES)
            if form.is_valid(): # All validation rules pass
                 obj = form.save(commit=False)
                 obj.user_id = 15
                 obj.save()

How can I do it with a `django-rest-framework` serializer object?

    @api_view([&#39;POST&#39;,&#39;GET&#39;])
    def upload_serializers(request):
        if request.method == &#39;POST&#39;:
             serializer = FilesSerializer(data=request.DATA, files=request.FILES)
             if serializer.is_valid():
                  serializer.save()

Editing django-rest-framework serializer object before save

I am beginner in Django REST framework and need your advice. I am developing a web service. The service has to provide REST interface to other services. The REST interface, which I need to implement, is not working with my models directly (I mean the get, put, post, delete operations). Instead, it provides other services with some calculation results. On a request my service makes some calculations and just returns the results back (doesn&#39;t store the results in its own database).  

Below is my understanding of how that REST interface could be implemented. Correct me, if I am wrong.  

 1. Create class which makes the calculations. Name it &#39;CalcClass&#39;. CalcClass uses the models in its work.  
 * Params necessary for the calculations are passed to the constructor.  
 * Implement the calc operation. It returns results as &#39;ResultClass&#39;.  
 2. Create ResultClass.  
 * Derived from object.  
 * It just only has attributes containing the calc results.  
 * One part of the calc results is represented as tuple of tuples. As I understand, it would be better for further serialization to implement a separate class for those results and add list of such objects to ResultClass.  
 3. Create Serializer for ResultClass.  
 * Derive from serializers.Serializer.  
 * The calc results are read-only, so use mostly Field class for fields, instead of specialized classes, such as IntegerField.  
 * I should not impl save() method neither on ResultClass, nor on Serializer, because I am not going to store the results (I just want to return them on request).  
 * Impl serializer for nested results (remember tuple of tuples mentioned above).  
 4. Create View to return calculation results.  
 * Derive from APIView.  
 * Need just get().  
 * In get() create CalcClass with params retrieved from the request, call its calc(), get ResultClass, create Serializer and pass the ResultClass to it, return Response(serializer.data).  
 5. URLs  
 * There is no api root in my case. I should just have URLs to get various calc results (calc with diff params).  
 * Add calling format_suffix_patterns for api browsing.  

Did I miss something? Is the approach is correct in general?

Django REST framework: non-model serializer

I know there are a lot of questions about it, but I tried several solutions, and nothing works.

In my django app I have a form:

    &lt;form method=&#39;post&#39;&gt;
        &lt;button type=&#39;submit&#39;&gt;Send&lt;/button&gt;
    &lt;/form&gt;

I wan&#39;t to disable the button once the user has submitted the form. Using other questions, I tried several things, like:
 
    &lt;button type=&#39;submit&#39; onclick=&quot;this.disabled=true&quot;&gt;Send&lt;/button&gt;

When I click, the button is disabled... but the form is not submitted. And for each try I had the same issue: either the button is disabled or the form is submitted. I can&#39;t find how to do both...

I&#39;m using Chrome. Any idea on why I have this problem?  Thank you for your help.

Disable button after submit with jQuery

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()

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	Guy Bowden	View Question on Stackoverflow
Solution 1 - Django	Aamir Rind	View Answer on Stackoverflow
Solution 2 - Django	Srinivas Reddy Thatiparthy	View Answer on Stackoverflow

How to group by AND aggregate with Django

Django Problem Overview

Django Solutions

Solution 1 - Django

Solution 2 - Django

SQL versus noSQL (speed)

Spring MVC How take the parameter value of a GET HTTP Request in my controller method?

Attributions