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Django and SQLAlchemy integration

Project description

Django Sorcery

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Django Framework integration with SQLAlchemy

SQLAlchemy is an excellent orm. And Django is a great framework, until you decide not to use Django ORM. This library provides utilities, helpers and configurations to ease the pain of using SQLAlchemy with Django. It aims to provide a similar development experience to building a Django application with Django ORM, except with SQLAlchemy.

Installation

pip install django-sorcery

Quick Start

Lets start by creating a site:

$ django-admin startproject mysite

And lets create an app:

$ cd mysite
$ python manage.py startapp polls

This will create a polls app with standard django app layout:

$ tree
.
├── manage.py
├── polls
│   ├── admin.py
│   ├── apps.py
│   ├── __init__.py
│   ├── migrations
│   │   └── __init__.py
│   ├── models.py
│   ├── tests.py
│   └── views.py
└── mysite
    ├── __init__.py
    ├── settings.py
    ├── urls.py
    └── wsgi.py

3 directories, 12 files

And lets add our polls app in INSTALLED_APPS in mysite/settings.py:

INSTALLED_APPS = [
    'polls.apps.PollsConfig',
    'django.contrib.admin',
    'django.contrib.auth',
    'django.contrib.contenttypes',
    'django.contrib.sessions',
    'django.contrib.messages',
    'django.contrib.staticfiles',
]

Now we’re going to make a twist and start building our app with sqlalchemy. Lets define our models in polls/models.py:

from django_sorcery.db import databases


db = databases.get("default")


class Question(db.Model):
    pk = db.Column(db.Integer(), autoincrement=True, primary_key=True)
    question_text = db.Column(db.String(length=200))
    pub_date = db.Column(db.DateTime())


class Choice(db.Model):
    pk = db.Column(db.Integer(), autoincrement=True, primary_key=True)
    choice_text = db.Column(db.String(length=200))
    votes = db.Column(db.Integer(), default=0)

    question = db.ManyToOne(Question, backref=db.backref("choices", cascade="all, delete-orphan"))


db.configure_mappers()
db.create_all()

Right now, we have enough to hop in django shell:

$ python manage.py shell

>>> from polls.models import Choice, Question, db  # Import the model classes and the db

# we have no choices or questions in db yet
>>> Choice.query.all()
[]
>>> Question.query.all()
[]

# Lets create a new question
>>> from django.utils import timezone
>>> q = Question(question_text="What's new?", pub_date=timezone.now())
>>> q
Question(pk=None, pub_date=datetime.datetime(2018, 5, 19, 0, 54, 20, 778186, tzinfo=<UTC>), question_text="What's new?")

# lets save our question, we need to add our question to the db
>>> db.add(q)

# at this point the question is in pending state
>>> db.new
IdentitySet([Question(pk=None, pub_date=datetime.datetime(2018, 5, 19, 0, 54, 20, 778186, tzinfo=<UTC>), question_text="What's new?")])

# lets flush to the database
>>> db.flush()

# at this point our question is in persistent state and will receive a primary key
>>> q.pk
1

# lets change the question text
>>> q.question_text = "What's up?"
>>> db.flush()

# Question.objects and Question.query are both query properties that return a query object bound to db
>>> Question.objects
<django_sorcery.db.query.Query at 0x7feb1c7899e8>
>>> Question.query
<django_sorcery.db.query.Query at 0x7feb1c9377f0>

# and lets see all the questions
>>> Question.objects.all()
[Question(pk=1, pub_date=datetime.datetime(2018, 5, 19, 0, 54, 20, 778186, tzinfo=<UTC>), question_text="What's up?")]

>>> exit()

Let’s add a couple of views in polls/views.py, starting with a list view:

from django.shortcuts import render
from django.template import loader
from django.http import HttpResponseRedirect
from django.urls import reverse

from django_sorcery.shortcuts import get_object_or_404

from .models import Question, Choice, db

def index(request):
    latest_question_list = Question.objects.order_by(Question.pub_date.desc())[:5]
    context = {'latest_question_list': latest_question_list}
    return render(request, 'polls/index.html', context)


def detail(request, question_id):
    question = get_object_or_404(Question, pk=question_id)
    return render(request, 'polls/detail.html', {'question': question})


def results(request, question_id):
    question = get_object_or_404(Question, pk=question_id)
    return render(request, 'polls/results.html', {'question': question})


def vote(request, question_id):
    question = get_object_or_404(Question, pk=question_id)

    selected_choice = Choice.query.filter(
        Choice.question == question,
        Choice.pk == request.POST['choice'],
    ).one_or_none()

    if not selected_choice:
        return render(request, 'polls/detail.html', {
            'question': question,
            'error_message': "You didn't select a choice.",
        })

    selected_choice.votes += 1
    db.flush()
    return HttpResponseRedirect(reverse('polls:results', args=(question.pk,)))

and register the view in polls/urls.py:

from django.urls import path

from . import views


app_name = 'polls'
urlpatterns = [
    path('', views.index, name='index'),
    path('<int:question_id>/', views.detail, name='detail'),
    path('<int:question_id>/results', views.results, name='results'),
    path('<int:question_id>/vote', views.vote, name='vote'),
]

and register the SQLAlchemyMiddleware to provide unit-of-work per request pattern:

MIDDLEWARE = [
    'django_sorcery.db.middleware.SQLAlchemyMiddleware',
    # ...
]

and add some templates:

polls/templates/polls/index.html:

{% if latest_question_list %}
<ul>
{% for question in latest_question_list %}
<li><a href="{% url 'polls:detail' question.pk %}">{{ question.question_text }}</a></li>
{% endfor %}
</ul>
{% else %}
<p>No polls are available.</p>
{% endif %}

polls/templates/polls/detail.html:

<h1>{{ question.question_text }}</h1>

{% if error_message %}<p><strong>{{ error_message }}</strong></p>{% endif %}

<form action="{% url 'polls:vote' question.pk %}" method="post">
{% csrf_token %}
{% for choice in question.choices %}
    <input type="radio" name="choice" id="choice{{ forloop.counter }}" value="{{ choice.pk }}" />
    <label for="choice{{ forloop.counter }}">{{ choice.choice_text }}</label><br />
{% endfor %}
<input type="submit" value="Vote" />
</form>

polls/templates/polls/results.html:

<h1>{{ question.question_text }}</h1>

<ul>
{% for choice in question.choices %}
    <li>{{ choice.choice_text }} -- {{ choice.votes }} vote{{ choice.votes|pluralize }}</li>
{% endfor %}
</ul>

<a href="{% url 'polls:detail' question.pk %}">Vote again?</a>

This is all fine but we can do one better using generic views. Lets adjust our views in polls/views.py:

from django.shortcuts import render
from django.http import HttpResponseRedirect
from django.urls import reverse

from django_sorcery.shortcuts import get_object_or_404
from django_sorcery import views

from .models import Question, Choice, db


class IndexView(views.ListView):
    template_name = 'polls/index.html'
    context_object_name = 'latest_question_list'

    def get_queryset(self):
        return Question.objects.order_by(Question.pub_date.desc())[:5]


class DetailView(views.DetailView):
    model = Question
    session = db
    template_name = 'polls/detail.html'


class ResultsView(DetailView):
    template_name = 'polls/results.html'


def vote(request, question_id):
    question = get_object_or_404(Question, pk=question_id)

    selected_choice = Choice.query.filter(
        Choice.question == question,
        Choice.pk == request.POST['choice'],
    ).one_or_none()

    if not selected_choice:
        return render(request, 'polls/detail.html', {
            'question': question,
            'error_message': "You didn't select a choice.",
        })

    selected_choice.votes += 1
    db.flush()
    return HttpResponseRedirect(reverse('polls:results', args=(question.pk,)))

and adjust the polls/urls.py like:

from django.urls import path

from . import views


app_name = 'polls'
urlpatterns = [
    path('', views.IndexView.as_view(), name='index'),
    path('<int:pk>/', views.DetailView.as_view(), name='detail'),
    path('<int:pk>/results', views.ResultsView.as_view(), name='results'),
    path('<int:question_id>/vote', views.vote, name='vote'),
]

The default values for template_name and context_object_name are similar to django’s generic views. If we handn’t defined those the default for template names would’ve been polls/question_detail.html and polls/question_list.html for the detail and list template names, and question and question_list for context names for detail and list views.

This is all fine but we can even do one better using a viewset. Lets adjust our views in polls/views.py:

from django.http import HttpResponseRedirect
from django.urls import reverse, reverse_lazy

from django_sorcery.routers import action
from django_sorcery.viewsets import ModelViewSet

from .models import Question, Choice, db


class PollsViewSet(ModelViewSet):
    model = Question
    fields = "__all__"
    destroy_success_url = reverse_lazy("polls:question-list")

    def get_success_url(self):
        return reverse("polls:question-detail", kwargs={"pk": self.object.pk})

    @action(detail=True)
    def results(self, request, *args, **kwargs):
        return self.retrieve(request, *args, **kwargs)

    @action(detail=True, methods=["POST"])
    def vote(self, request, *args, **kwargs):
        self.object = self.get_object()

        selected_choice = Choice.query.filter(
            Choice.question == self.object, Choice.pk == request.POST.get("choice")
        ).one_or_none()

        if not selected_choice:
            context = self.get_detail_context_data(object=self.object)
            context["error_message"] = "You didn't select a choice."
            self.action = "retrieve"
            return self.render_to_response(context)

        selected_choice.votes += 1
        db.flush()
        return HttpResponseRedirect(reverse("polls:question-results", args=(self.object.pk,)))

And adjusting our polls/urls.py like:

from django.urls import path, include

from django_sorcery.routers import SimpleRouter

from . import views

router = SimpleRouter()
router.register("", views.PollsViewSet)

app_name = "polls"
urlpatterns = [path("", include(router.urls))]

With these changes we’ll have the following urls:

$ ./manage.py run show_urls
/polls/     polls.views.PollsViewSet        polls:question-list
/polls/<pk>/        polls.views.PollsViewSet        polls:question-detail
/polls/<pk>/delete/ polls.views.PollsViewSet        polls:question-destroy
/polls/<pk>/edit/   polls.views.PollsViewSet        polls:question-edit
/polls/<pk>/results/        polls.views.PollsViewSet        polls:question-results
/polls/<pk>/vote/   polls.views.PollsViewSet        polls:question-vote
/polls/new/ polls.views.PollsViewSet        polls:question-new

This will map the following operations to following actions on the viewset:

Method Path Action Route Name
GET /polls/ list question-list
POST /polls/ create question-list
GET /polls/new/ new question-new
GET /polls/1/ retrieve question-detail
POST /polls/1/ update question-detail
PUT /polls/1/ update question-detail
PATCH /polls/1/ update question-detail
DELETE /polls/1/ destroy question-detail
GET /polls/1/edit/ edit question-edit
GET /polls/1/delete/ confirm_destoy question-delete
POST /polls/1/delete/ destoy question-delete

Now, lets add an inline formset to be able to add choices to questions, adjust polls/views.py:

from django.http import HttpResponseRedirect
from django.urls import reverse, reverse_lazy

from django_sorcery.routers import action
from django_sorcery.viewsets import ModelViewSet
from django_sorcery.formsets import inlineformset_factory

from .models import Question, Choice, db


ChoiceFormSet = inlineformset_factory(relation=Question.choices, fields=(Choice.choice_text.key,), session=db)


class PollsViewSet(ModelViewSet):
    model = Question
    fields = (Question.question_text.key, Question.pub_date.key)
    destroy_success_url = reverse_lazy("polls:question-list")

    def get_success_url(self):
        return reverse("polls:question-detail", kwargs={"pk": self.object.pk})

    def get_form_context_data(self, **kwargs):
        kwargs["choice_formset"] = self.get_choice_formset()
        return super(PollsViewSet, self).get_form_context_data(**kwargs)

    def get_choice_formset(self, instance=None):
        if not hasattr(self, "_choice_formset"):
            instance = instance or self.object
            self._choice_formset = ChoiceFormSet(
                instance=instance, data=self.request.POST if self.request.POST else None
            )

        return self._choice_formset

    def process_form(self, form):
        if form.is_valid() and self.get_choice_formset(instance=form.instance).is_valid():
            return self.form_valid(form)

        return form.invalid(self, form)

    def form_valid(self, form):
        self.object = form.save()
        self.object.choices = self.get_choice_formset().save()
        db.flush()
        return HttpResponseRedirect(self.get_success_url())

    @action(detail=True)
    def results(self, request, *args, **kwargs):
        return self.retrieve(request, *args, **kwargs)

    @action(detail=True, methods=["POST"])
    def vote(self, request, *args, **kwargs):
        self.object = self.get_object()

        selected_choice = Choice.query.filter(
            Choice.question == self.object, Choice.pk == request.POST.get("choice")
        ).one_or_none()

        if not selected_choice:
            context = self.get_detail_context_data(object=self.object)
            context["error_message"] = "You didn't select a choice."
            self.action = "retrieve"
            return self.render_to_response(context)

        selected_choice.votes += 1
        db.flush()
        return HttpResponseRedirect(reverse("polls:question-results", args=(self.object.pk,)))

And add choice_formset in the polls/templates/question_edit.html and polls/templates/question_edit.html

<form ... >
    ...
    {{ choice_formset }}
    ...
</form >

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