Where to write predefined queries in django? - sql

Question

I am working with a team of engineers, and this is my first Django project.
Since I have done SQL before, I chose to write the predefined queries that the front-end developers are supposed to use to build this page (result set paging, simple find etc.).
I just learned Django QuerySet, and I am ready to use it, but I do not know on which file/class to write them.
Should I write them as methods inside each class in models.py? Django documentation simply writes them in the shell, and I haven't read it say where to put them.

Answer 1

Generally, the Django pattern is that you will write your queries in your views in the views.py file. Here you will take each of your predefined queries for a given URL and return a response that renders a template (that presumably your front end team will build with you.) or returns a JSON response (for example through Django Rest Framework for an SPA front-end).
The tutorial is strong on this, so that may be a better bet for where to put things than the docs itself.
Queries can be run anywhere, but django is built to receive Requests through the URL schema, and return a response. This is typically done in the views.py, and each view is generally called by a line in the urls.py file.
If you're particularly interested in following the fat models approach and putting them there, then you might be interested in the Manager objects, which are what define querysets that you get through, for example MyModel.objects.all()
My example view (for a class based view, which provides information about a list of matches:
class MatchList(generics.ListCreateAPIView):
"""
Retrieve, update or delete a Match.
"""
queryset = Match.objects.all()
serializer_class = MatchSerialiser
That queryset could be anything, though.
A function based view with a different queryset would be:
def event(request, event_slug):
from .models import Event, Comment, Profile
event = Event.objects.get(event_url=event_slug)
future_events = Event.objects.filter(date__gt=event.date)
comments = Comment.objects.select_related('user').filter(event=event)
final_comments = []
return render(request, 'core/event.html', {"event": event, "future_events": future_events})
edit: That second example is quite old, and the query would be better refactored to:
future_events=Event.objects.filter(date__gt=event.date).select_related('comments')
Edit edit: It's worth pointing out, QuerySet isn't a language, in the way that you're using it. It's django's API for the Object Relational Mapper that sits on top of the database, in the same way that SQLAlchemy also does - in fact, you can swap out or use SQLAlchemy instead of using the Django ORM, if you really wanted. Mostly you'll hear people talking about the Django ORM. :)

Answer 2

If you have some model SomeModel and you wanted to access its objects via a raw SQL query you would do: SomeModel.objects.raw(raw_query).
For example: SomeModel.objects.raw('SELECT * FROM myapp_somemodel')
https://docs.djangoproject.com/en/1.11/topics/db/sql/#performing-raw-queries

Answer 3

Django file structure:
app/
models.py
views.py
urls.py
templates/
app/
my_template.html
In models.py
class MyModel(models.Model):
#field definition and relations
In views.py:
from .models import MyModel
def my_view():
my_model = MyModel.objects.all() #here you use the querysets
return render('my_template.html', {'my_model': my_model}) #pass the object to the template
In the urls.py
from .views import my_view
url(r'^myurl/$', my_view, name='my_view'), # here you write the url that points to your view
And finally in my_template.html
# display the data using django template
{% for obj in object_list %}
<p>{{ obj }}</p>
{% endfor %}