Wednesday, May 11, 2016

Python : django 1.8 + PostgreSQL shortened tutorial

This article is a compressed version of the first 2 chapters of django official tutorial. It does not explain anything but simply goes through the basic procedures to create a application server in a short time.

Installation instructions


Django 

sudo pip install django

PostgreSQL 

sudo apt-get install postgresql postgresql-client postgresql-server-dev-9.4 [pgadmin3]
Install database binding for django : 

sudo apt-get install python-dev # necessary to compile the binder
sudo pip install psycopg2

Configuration


Database access

Add a demo user from shell and set its password to 'user' 

sudo adduser spvuser



Log into postgres and create a database for that user 

sudo -u postgres psql
postgres=# CREATE USER spvclient WITH PASSWORD 'user';
postgres=# CREATE DATABASE spvdatabase OWNER spvclient ;
postgres=# \q

Check that the new database is accessible 

psql -d spvdatabase -U spvuser
spvdatabase=> \q # quit



Finally, edit postgres configuration file

sudo nano /etc/postgres/main/9.4/pg_hba.conf

Replace ident or peer with trust 

local all all trust

Develop your own site

Create project 

django-admin startproject poc_supervisor

Run server (default: 127.0.0.1:8000) : 

python manage.py runserver

Ctrl+C to quit

Create an app (let's call it supervisor):

python manage.py startapp supervisor


Edit supervisor/apps.py (app generic configuration information):

from django.apps import AppConfig

class SupervisorConfig(AppConfig):
    name = "supervisor"
   verbose_name = "POC 5.5 Supervision interface"
  
[cd supervisor]

Create a view

- edit views.py

from django.http import HttpResponse


def index(request):
    return HttpResponse("Hello, world. You're at the polls index.")

 - create a file named urls.py with the following code to map view to URL 

from django.conf.urls import url
from . import views

urlpatterns = [
    # ex: /supervisor/
    url(r'^$', views.index, name='index'),
]

[cd ..]


  - edit poc_supervisor/urls.py to point new view to root 

from django.conf.urls import include, url
from django.contrib import admin

urlpatterns = [
    url(r'^supervisor/', include('supervisor.urls')),
    url(r'^admin/', admin.site.urls),
]
 
- Verify

python manage.py runserver

and open 127.0.0.1:8000/supervisor

 

Django Database settings

Edit poc_supervisor/settings.py and replace existing DATABASES descriptor with : 
DATABASES = {

'default' : {
         'ENGINE' :  'django.db.backends.postgresql_psycopg2',
         'NAME' : 'spvdatabase',
         'USER' : 'spvuser',
         'PASSWORD': 'user',
         'HOST' : '',
    }
}

Generate database tables for all INSTALLED_APPS 
 
python manage.py migrate

Verify that tables have been created 
 
psql -d spvdatabase -U spvuser
spvdatabase=> \dt

You should see a list of tables 
public | auth_group | table | spvuser
public | auth_group_persmissions  | table | spvuser

...

public | django_session | table | spvuser


spvdatabase=> \q # quit

Create a database model for your app


For example for this model:


 

Edit supervisor/models.py

    from django.db import models


    # Create your models here.


    ##############################

    ################
    #
    # Custom validators
    #
    ##############################################
    def isStatusValid(value):
      """
      Checks the validity of SystemData status field
      """
      valid_status_list = ['DEFAULT', 'NORMAL', 'NOT_AVAILABLE', 'NO_DEVICE', 'PROTOCOL_ERROR']
      isValid = False
      if value in valid_status_list:
        isValid = True
       
      return isValid

    class DeviceProxy(models.Model):
        name = models.CharField(max_length=64, unique=True)
        description = models.TextField()
        ip_address = models.IPAddressField()
        subnet_mask = models.IPAddressField()
        port = models.IntegerField(default=47808)
       
        def __str__(self):
          return self.name + " (%s)"%self.ip_address

    class SystemData(models.Model):
        identifier = models.IntegerField(primary_key=True)
        description = models.CharField(max_length=64, unique=True)
        resolution = models.DecimalField(max_digits=3, decimal_places=3)
        unit = models.CharField(max_length=10)
       
        def __str__(self):
          return self.identfier + " : %s"%self.description
       
    class SystemDataAcquisition(models.Model):
        # Delete all system data that belongs to deleted device proxy
        device_proxy = models.ForeignKey(DeviceProxy, on_delete=models.CASCADE)
        identifier = models.ForeignKey(SystemData, on_delete=models.CASCADE)
       
        timestamp = models.DateTimeField()
        status = models.CharField(max_length=32, validators=[isStatusValid])
        value = models.DecimalField(max_digits=10, decimal_places=2)
       
        def __str__(self):
          return self.identifier + " = %s %s"%(str(self.value), self.unit) 



Add your app to INSTALLED_APPS in poc_supervisor/settings.py:

INSTALLED_APPS = (
    'supervisor.apps.SupervisorConfig',
    ...

Activate your model

python manage.py makemigrations supervisor
python manage.py migrate

Check this link if you want to play with your model with the django shell.

Add an administration interface 

python manage.py createsuperuser

and enter the user name (e.g. 'admin'), an email address for this user and a password twice. Verify :
python manage.py runserver

and open 127.0.0.1/admin and log yourself.

Add administration option on database entries

Edit supervisor/admin.py 
 
from .models import SystemData, DeviceProxy
 

admin.site.register(SystemData)br />
admin.site.register(DeviceProxy)

Run verification step again.

2 comments:

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