Re: Pagination breaks in ListView after migrating from Django 1.11 to 2.2 with SQLite

[Szabolcs Hodossy]

Thanks for the help, I have checked those release notes, but I was not able
to identify the related change (neither subquery nor __in lookup). I wanted
to give you a deeper look into the code, but during that I managed to
isolate the issue. It seems that the '__in' lookups previously accepted
objects and automatically extracted the referenced columns in case of
Foreign Key fields, but that is not valid now. I added `values('id')`
everywhere, and it solved the problem. I am not sure how to feel about this
change, as 'id' is automatically created.

Br,
Szabolcs

On Tue, Apr 23, 2019 at 4:39 PM Simon Charette  wrote:

> I assume you are either using a Subquery annotation that returns
> multiple results or an __in lookup against a query with multiple columns.
>
> I vaguely remember something changed in this area but it was documented
> in one of the 2.0, 2.1 or 2.2 release notes.
>
> Best,
> Simon
>
> Le mardi 23 avril 2019 10:31:43 UTC-4, hodossy...@gmail.com a écrit :
>>
>> Hello,
>>
>> I am facing the following issue after upgrading to 2.2 from 1.11. Here is
>> the stack trace:
>>
>> Traceback (most recent call last):
>>   File "(...)\.env\lib\site-packages\django\db\backends\utils.py", line
>> 84, in _execute
>> return self.cursor.execute(sql, params)
>>   File "(...)\.env\lib\site-packages\django\db\backends\sqlite3\base.py",
>> line 383, in execute
>> return Database.Cursor.execute(self, query, params)
>> sqlite3.OperationalError: only a single result allowed for a SELECT that
>> is part of an expression
>>
>> The above exception was the direct cause of the following exception:
>>
>> Traceback (most recent call last):
>>   File "(...)\dashboard\deployment\tests\test_view.py", line 53, in
>> test_display_list_view
>> response = self.client.get(self.url_my_list)
>>   File "(...)\.env\lib\site-packages\django\test\client.py", line 535, in
>> get
>> response = super().get(path, data=data, secure=secure, **extra)
>>   File "(...)\.env\lib\site-packages\django\test\client.py", line 347, in
>> get
>> **extra,
>>   File "(...)\.env\lib\site-packages\django\test\client.py", line 422, in
>> generic
>> return self.request(**r)
>>   File "(...)\.env\lib\site-packages\django\test\client.py", line 503, in
>> request
>> raise exc_value
>>   File "(...)\.env\lib\site-packages\django\core\handlers\exception.py",
>> line 34, in inner
>> response = get_response(request)
>>   File "(...)\.env\lib\site-packages\django\core\handlers\base.py", line
>> 115, in _get_response
>> response = self.process_exception_by_middleware(e, request)
>>   File "(...)\.env\lib\site-packages\django\core\handlers\base.py", line
>> 113, in _get_response
>> response = wrapped_callback(request, *callback_args,
>> **callback_kwargs)
>>   File "(...)\.env\lib\site-packages\django\views\generic\base.py", line
>> 71, in view
>> return self.dispatch(request, *args, **kwargs)
>>   File "(...)\.env\lib\site-packages\django\contrib\auth\mixins.py", line
>> 52, in dispatch
>> return super().dispatch(request, *args, **kwargs)
>>   File "(...)\.env\lib\site-packages\django\views\generic\base.py", line
>> 97, in dispatch
>> return handler(request, *args, **kwargs)
>>   File "(...)\.env\lib\site-packages\django\views\generic\list.py", line
>> 157, in get
>> context = self.get_context_data()
>>   File "(...)\dashboard\deployment\views.py", line 53, in get_context_data
>> context = super().get_context_data(**kwargs)
>>   File "(...)\.env\lib\site-packages\django\views\generic\list.py", line
>> 119, in get_context_data
>> paginator, page, queryset, is_paginated =
>> self.paginate_queryset(queryset, page_size)
>>   File "(...)\.env\lib\site-packages\django\views\generic\list.py", line
>> 69, in paginate_queryset
>> page = paginator.page(page_number)
>>   File "(...)\.env\lib\site-packages\django\core\paginator.py", line 70,
>> in page
>> number = self.validate_number(number)
>>   File "(...)\.env\lib\site-packages\django\core\paginator.py", line 48,
>> in validate_number
>> if number > self.num_pages:
>>   File "(...)\.env\lib\site-packages\django\utils\functional.py", line
>> 80, in __get__
>> res = instance.__dict__[self.name] = self.func(instance)
>>   File "(...)\.env\lib\site-packages\django\core\paginator.py", line 97,
>> in num_pages
>> if self.count == 0 and not self.allow_empty_first_page:
>>   File "(...)\.env\lib\site-packages\django\utils\functional.py", line
>> 80, in __get__
>> res = instance.__dict__[self.name] = self.func(instance)
>>   *File "(...)\.env\lib\site-packages\django\core\paginator.py", line
>> 91, in count*
>> *return c()*
>>   File "(...)\.env\lib\site-packages\django\db\models\query.py", line
>> 392, in count
>> return self.query.get_count(using=self.db)
>>   File "(...)\.env\lib\site-packages\django\db\models\sql\query.py", line
>> 504, in get_count
>> number = obj.get_aggregation(using, ['__count'])['__count']
>>   File "(...)\.env\li

Re: Different database types use in a single Django project

[Szabolcs Hodossy]

Hi Bbake,

You can also use a multi DB setup
 (I suggest
routers), and follow this guide to integrate a Mongo backend:
https://medium.freecodecamp.org/using-django-with-mongodb-by-adding-just-one-line-of-code-c386a298e179

One drawback that you lose relationships across DBs, but I think you
already prepared for that.

Hope this helps,
Szabolcs

On Fri, May 10, 2019 at 2:10 PM Chetan Ganji  wrote:

> Hi Bbake,
>
> Django Class Based Views and Models are wired for relational databases
> only. If you want to use MongoDB with django you have to say bye bye to CBV
> and Django ORM. There are some third party libraries to map django models
> to mongo, but IDK how good they are for production use.
>
> One way to solve this problem is use Function Based Views for views where
> MongoDB will be used.
> You will have to access mongo db using a database driver like pymongo.
>
> If you just need to store the json data, another way to solve this problem
> is to use django and postgres database.
> PostgreSQL has JSON field, django also supports that. Check the official
> documents for more info.
> https://docs.djangoproject.com/en/2.2/ref/contrib/postgres/fields/
>
> If you find any more solutions, please let me know, as I also want to
> explore the options of using mongo with django.
> Thanks in advance.
>
>
> Regards,
> Chetan Ganji
> +91-900-483-4183
> ganji.che...@gmail.com
> http://ryucoder.in
>
>
> On Fri, May 10, 2019 at 5:27 PM Bbake Waikhom  wrote:
>
>> Is there any way that I can use different database type in a single
>> Django project like some model A will use SQL and some model B will use
>> MongoDB? Because in my project some data are better to store in a
>> relational database and some are better to store in a NoSQL database. I've
>> been searching for a while to achieve this but I couldn't find any
>> solution. Please let me know if there is a way. Thank you.
>>
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