Category Archives: django

A typical web application

Reduce Time to the First Byte – TTFB on web applications

How to speed up the time to the first byte and what are the causes of a long TTFB? Main causes are network and server-side and I will focus on server-side causes. I’m not covering any CMS here but you can try to apply some of these techniques starting from how to interpret the browser Timing.

Get reliable timing

Take a website with cache enabled: at the 9th visit on a page you can be sure your page is in cache, the connection with the webserver is alive, the SSL/TLS connection is established, the SQL queries are cached and so on. Open the network tab and enjoy your site speed: well, very few real users will experience that speed.

Here a comparison of a first time, no-cache connection to a nginx webserver explored with Chrome (F12 > Network > Timing) and a second request with the same page refreshed right after the first:

performance-01

I got a +420% on a first time request compared with a connected-and-cached case. To obtain a reliable result (1st figure) you should usually:

  • Wait several seconds after a previous call before doing anything, waiting for the webserver to close connection with the client
  • Add a ?string to the url of the page you’re visiting. Change the string every time you want a fresh page.
  • Ctrl+shift+R to reload the page

This technique bypass the Django view cache and similar cache systems on other framework. To check the framework cache impact, do a Ctrl+shift+R just after the first request obtaining a similar result of the 2nd figure. There are better ways to do the same, this is the easiest.

Break up the time report

Unpack the time report of the first-time request:

  • Connection setup (15% of the elapsed time in the example)
    • Queueing: slight, nothing to do.
    • Stalled: slight, nothing to do.
    • DNS lookup: slight, nothing to do.
    • Initial connection: significant, skip for now.
    • SSL: significant, client establish a SSL/TLS connection with the webserver. Disabling ciphers or tuning SSL can reduce the time but the priority here is best security for the visitor, not pure speed. However, take a look at this case study if you want to tune SSL/TLS for speed.
  • Request / response (85% of the elapsed time i.e.)
    • Request sent: slight, browser-related, nothing to do.
    • Waiting (TTFB): significant, time to first byte is the time the user wait after the request was sent to the web server. The waiting time includes:
      • Framework elaboration.
      • Database queries.
    • Content Download: significant, page size, network, server and client related. To speed up content download of a HTML page you should add compression: here an howto for nginx and for Apache webservers: these covers proxy servers, applying directly on a virtualhost is even simplier and the performance gain is huge.

Not surprisingly, the time of a first time request is elapsed most in Request / response than on connection setup. Among the Request / response times is the Waiting (TTFB) the prominent. Luckyly it is the same segment covered by cache mechanics of the framework and consequently is the most eroded passing from the first (not cached) to the second figure (cached by the framework). To erode the TTFB, database queries and elaboration must be optimized.

Optimize elaboration: program optimization

When Google, the web-giant behind the most used web search engine in history, try to suggest some tips to optimize PHP to programmers they react badly starting from daily programmers going up to the PHP team bureau.

In a long response, the PHP team teach Google how to program the web offering unsolicited advice offering “some thoughts aimed at debunking these claims” with stances like “Depending on the way PHP is set up on your host, echo can be slower than print in some cases”, a totally confusing comment for a real-world programmer.

Google put offline the PHP performance page that can be misleading but still contains valid optimization tips, especially if you compare with some of comments on php.net itself. Google have interests to speed and code optimization and the writer has the know-how to talk about it, the PHP team here just want to be right and defend their language and starting from good points crossed the line of scientific dialectic.

Program optimization mottos are:

Look for the best language that suits to your work and the best tools you can and look for programmers from the real-world sharing their approaches to the program optimization.

PHP team’s whining will not change the fact that avoiding SQL inside a loop like Google employee suggested is the right thing to do to enhance performance. This leads to database optimization.

Dude, where is my data?

The standard web application nowadays has this structure:

A typical web application

A typical web application: application server run the application so from now on  Рoversimplifying РI will treat application and application servers as synonyms.

After the client requests pass through the firewall, webserver serve static files and ask to Application server the dynamic content.

Cache server can serve application or web server but in this example the earlier has the control: an example of cache controlled by application is on the Django docs about Memcache, an example of cache by web server is the HTTP Redis module or the standard use of Varnish cache.

Database server (DBMS) stores the structured data for the application. DBMS on standard use cases can be optimized with little effort. More difficult is to optimize the way the web application get the data from the database.

Database query optimization: prefetch and avoid duplicates

To optimize database queries you have to check the timing, again. Depending on the language and framework you are using there are tools to get information about queries to optimize:

Since I’m using Python I go with Django Debug Toolbar, a de-facto standard for application profiling. Here a sample of SQL query timing on a PostgreSQL database:

Timing of SQL queries on Django Debug Toolbar.

Timing of SQL queries on Django Debug Toolbar.

The total time elapsed on queries is 137,07 milliseconds, the total number of queries executed are 90. Among these, 85 are duplicates. Below any query you’ll find how many times the same query is executed. The objective is to reduce the number of queries executed.

If you’re using Django, create a manager for your models.py to use like this:

class GenericManager(models.Manager):
    """
    prefetch_related: join via ORM
    select_related: join via database
    """
    related_models = ['people', 'photo_set']
    def per_organizer(self, orgz, **kwargs):
        p = kwargs.get('pubblicato', None)
        ret = self.filter(organizer = orgz)
        return ret

class People(models.Model):
    name = models.CharField(max_length=50)
    ...

class Party(models.Model):
    organizer = models.ForeignKey('People')
    objects   =  GenericManager()

class Photo(models.Model):
    party = models.ForeignKey('Party')
    ...

Then in views.py call your custom method on GenericManager:

def all_parties(request, organizer_name):
    party_organizer = People.objects.get(name=organizer_name)
    all_parties = Party.objects.per_organizer(party_organizer)
    return render(request, 'myfunnywebsite/parties.html', {
        'parties' : all_parties
    })

When you want to optimize data retreival for Party, instead of comb through objects.filter() methods on views.py you will fix only the per_organizer method like this:

class GenericManager(models.Manager):
    """
    prefetch_related: join via ORM
    select_related: join via database
    """
    related_models = ['people', 'photo_set']
    def per_organizer(self, orgz, **kwargs):
        ret = self.filter(organizer = orgz)
        return ret.prefetch_related(*self.related_models)

Using prefetch_related queries are grouped via ORM and all objects are available, avoiding many query duplicates. Here a result of this first optimization:

django_sql_query_debug_toolbar_2

  • Query number is dropped from 90 to 45
  • Query execution time dropped from 137,07 to 80,80 (-41%)

An alternative method is select_related, but in this case the ORM will produce a join and the above code will give an error because photo_set is not accessible in this way. If your models are structured in a way you got a better performance with select_related go with it but remember this limitation. In this use case the results of select_related are worse than prefetch_related.

Recap:

  • TTFB can be a symptom of server-side inefficiency but you have to profile your application server-side to find out
  • Check SQL timing
  • Reduce the number of queries
  • Optimize application code
  • Use cache systems, memory-based (redis, memcached) are the faster

In my experience, inefficient code and a lot of cache are a frail solution compared with the right balance between caching and query + program optimization.

If you’ve tried everything and the application is still slow, consider to rewrite it or even to change the framework you’re using if speed is critical. When any optimization failed, I went from a Drupal 6 to a fresh Django 1.8 installation, and Google understood the difference in milliseconds elapsed to download the pages during indexing:

downloadtime

Since you can’t win a fight with windmills, a fresh start may be the only effective option on the table.

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How to start programming in Python on Windows

To develop in Django can be confusing for a new Python developer but using Windows to develop in Django can be a major obstacle too.

How to choose the right IDE for Windows and how to find and install Python libraries? Below six fundamental resources to program with Python on Windows.

Bitnami Django Stack

For developer using Windows, Bitnami Django Stack is a life-saver. It raises you to the need of installing and configuring many libraries and simply create a Python / Django environment on your system. Even if you don’t want to use Django, it can be a great starting point to install Python and fundamental libraries you can extend via PyCharm.

PyCharm

complexlook2x

Screenshot: official website

JetBrains’ PyCharm is the multiplatform IDE to develop in Python. You can forget about the indentation issue and focus on programming. The autocomplete dropdown, the Python console, the easy management of DVCS systems (Git, Mercurial), the easy access to Python packages repositories will make it the tools for Python programming, especially in Windows where there are few alternatives than Linux. On Windows, rely on the Bitnami Django Stack you’re using to load the right libraries.

PyPI – Cheese Shop

PyPI is the repository of Python packages. Since the PyPI is nearly unpronounceable, you can call it Cheese Shop. Python was named by Guido van Rossum after the British comedy group Monty Python and the Cheese Shop is this sketch:

Contrary on the poor guy in the sketch, you will find all sort of cheese you need in the cheese shop.

Pip

Pip is the definitive tool for installing Python packages from Cheese shop on your environment. pip install package-name and you’ll get the package ready and running. Even more interesting is the pip install -r requirements.txt feature. It will install all the packages listed in the requirements.txt text file usually shipped with a package having some dependencies.

PgAdmin

pgadmin4-properties.png

Screenshot: official website

Django and PostgreSQL DBMS are a powerful couple. If you have to use a PostgreSQL database, the best interface you can use is PgAdmin.

Django Packages

Django Packages is the Hitchhiker guide to the cheese shop. You’ve to choose a REST framework but you don’t want to marry with a unreliable partner? You need a good photo gallery and you want to get the best django app to implement in your django application? Django packages will guide you to the best solution for your needs.

django-packages

Any feature has a comparison matrix, where all projects are listed in columns where these criterion, elaborated from Github, are contemplated:

  • Project status (production, beta, alpha)
  • Commit frequency in the repository
  • How many times the project was forked
  • Who work on the project
  • Link to online documentation
  • Features comparison

If you’re coming from a CMS like Drupal here some tips to how to approach a Model-View-Controller like Django, starting from the Entity-Relationship model.

Personal note: Back in the 1998 I start to develop application for the web using ASP and PHP and dependencies weren’t an issue since these languages are for the web. Developing in Python is more challenging and really more fun than programming in PHP. You have a powerful multipurpose language with a ton of libraries competing in a far larger arena than the web development. Not surprising, Google use this language extensively as of some popular web services like Pinterest and Instagram: these last two are using Django.

Read also on the same topic: Django development on Virtualbox: step by step setup

From Drupal to Django: how to migrate contents

In a recent article¬†I explain the motivations for an upgrade from a no longer maintained Drupal 6 installation to¬†Django 1.8. I will now cover more in detail the migration techniques adopted in the upgrade and I’ll deepen the models and the relationships.

Structure

If you’re a drupaler, you’re familiar with the node/NID/edit and the node/add/TYPE pages:

A-New-Page-Drupal-6-Sandbox

Here we have two visible fields: Title and Body. One is an input type text and the other a texarea. The good Form API provided by Drupal calls these two types textfield and textarea. However if you use the Content type creation interface you don’t see any of these, just declare some field types and you’ll see the form populating with new fields after the addition.

It’s similar in Django but you haven’t to pass to a graphical interface to do this: structure is code-driven and the side effect is the ability to put on revision almost anything. You can choose between different field types that will be reflected in database and on the user interface.

Here what the Drupal Body and Title fields looks like in a model called Article:

# models.py
from django.db import models
from tinymce import models as tinymce_models
# Articles
class Article(models.Model):
    title       = models.CharField(max_length=250,null=False, blank=False)
    body        = tinymce_models.HTMLField(blank=True, default='')

The TinyMCE part require TinyMCE app installed and configured.¬†If you’re new to Django read and follow the great Writing your first Django app¬†to understand the basics, e.g the difference between a project and an app or the following sections will sound pretty obscure.

After editing your projectname/appname/models.py file you can now apply the changes in your app via makemigrations (create a migration file for the changes in the database) and migrate (apply the migrations inside the migration files).

In a real world scenario these two fields alone aren’t enough neither in a Drupal 6.¬†These information are all presented by default in any type on Drupal 6:

authoring-info

Drupal 6 treats author as entities you can search through an autocomplete field, and date as a pseudo-ISO 8601 date field. The author field is a link to the User table in Drupal. In Django a similar user model¬†exists but if you want to unchain the access to the admin backend and the authorship it’s simpler to¬†create a custom author model and later associate this with the real user model.

sport3_uml

E-R of our app where migrate the Drupal contents to.

from django.db import models
from tinymce import models as tinymce_models
# Authors
class Author(models.Model):
    alias       = models.CharField(max_length=100)
    name        = models.CharField(max_length=100, null=True, blank=True)
    surname     = models.CharField(max_length=100, null=True, blank=True)
# Articles
class Article(models.Model):
    author      = models.ForeignKey('Author', verbose_name='Authored by')
    title       = models.CharField(max_length=250,null=False, blank=False)
    body        = tinymce_models.HTMLField(blank=True, default='')
    publishing_date = models.DateTimeField(auto_now=False, auto_now_add=False, verbose_name='First published on')

As you can see in the Entity-Relationship diagram one¬†Article must have one and only one Author, but many¬†Articles can have the same Author. This is called Many-to-one relationship¬†and it’s represented in Django as a foreign key from the destination “many” model (e.g. Article) to the “one” model (Author).

The Article.publishing_date field is where publishing date and time are stored and, clicking on the text field, a calendar popup is presented to choose the day and hour, with a useful “now” shortcut to populate the field with the current time.

calendario

How a calendar is represented in a DateTime field.

Now that the basic fields are in the right place you can makemigrations / migrate again to update your app, restarting the webserver to apply the changes.

Attachments and images

Drupal is shipped with the ability to upload files and images to nodes. Django has two different field for this: FileField and ImageField. Before continuing we have to rethink our E-R model to allow attachments.

sport3_uml

 

The model.py code is:

from django.db import models
from tinymce import models as tinymce_models
# Authors
class Author(models.Model):
    alias       = models.CharField(max_length=100)
    name        = models.CharField(max_length=100, null=True, blank=True)
    surname     = models.CharField(max_length=100, null=True, blank=True)
# Articles
class Article(models.Model):
    author      = models.ForeignKey('Author', verbose_name='Authored by')
    title       = models.CharField(max_length=250,null=False, blank=False)
    body        = tinymce_models.HTMLField(blank=True, default='')
    publishing_date = models.DateTimeField(auto_now=False, auto_now_add=False, verbose_name='First published on')
# Attachments
class Attachments(models.Model):
    description = models.CharField(max_length=255, default='', blank=True)
    list = models.BooleanField(default=True)
    file = models.FileField(upload_to='attachments_directory', max_length=255)

Images are similar: if you want to enrich your model with images you can create another model like Attachments but with an ImageField instead. Remember to use a different upload_to directory in order to keep the attachments and images separated.

We miss the last one field to complete our models: path. Django comes with an useful SlugField that as of Django 1.8 allows only ASCII characters and can be mapped to another field, the title for example.

from django.db import models
from tinymce import models as tinymce_models
# Articles
class Article(models.Model):
    author      = models.ForeignKey('Author', verbose_name='Authored by')
    title       = models.CharField(max_length=250,null=False, blank=False)
    body        = tinymce_models.HTMLField(blank=True, default='')
    publishing_date = models.DateTimeField(auto_now=False, auto_now_add=False, verbose_name='First published on')

Keep in mind that a SlugField differs from a Drupal path field because it doesn’t allow slashes. Consider a path like this:

news/news-title

In Drupal you will have a A) view with the path news and the argument news title or B) a fake path generated by pathauto or similar modules. In years of Drupal development, I can affirm that the B option is the typical easy way that turns into a nightmare of maintainance. Django core as far as I know allows only the A choice, so if you want a news view you have to declare it in urls.py and then in views.py as stated in official documentation.

  • news/: the news root path, coupled with the view
  • news-title: the ¬†argument passed to the view and¬†the SlugField content for an article. It must be unique to be used as key to retreive an article but since it can be empty we cannot force it to has a value or to be unique at first. When all data are imported and fixed we can change this field to unique to improve database retrieval performance.

Categories

And what about categories? If you have a category named Section, and an article can be associated with only one Section, you have to create a Many-to-one relationship. As you see before, you have to put the foreign key in the N side of the relation, in this case Article, so the model Article will have a ForeignKey field referencing a specific section.

On the other hands if you have tags to associate to your article you have to create a Tag model with a Many-to-many relationship to the Article. Django will create an intermediate model storing the Article-Tag relationships.

Do not abuse of M2M relationships because each relation needs a separate table and the number of JOIN on database table will increase with side effects on the performance, not even perceivable on the first since Django ORM is very efficient. The event handling will be more difficult for a beginner since the many to many events occurs only when the parent models are saved and this require some experience if you need to add a custom action to a M2M event. If you design wisely your E-R model you have nothing to be scared of.

Migration techniques

Now that we have the destination models, fields and relationship we can import the content from Drupal. In the previous article I suggested to use Views Datasource module to create a JSON view to export content. Please read the Exporting the data from Drupal section inside the article before continue.

The obtained row is something like:

{
  [
    {
      {nid: '30004',
      domainsourceid: '2',
      nodepath: 'http://example.com/path/here',
      postdate: '2014-09-17T22:18:42+0200',
      nodebody: 'HTML TEXT HERE',
      nodetype: 'drupal type',
      nodetitle: 'Title here',
      nodeauthor: 'monty',
      nodetags: 'Drupal, dragonball, paintball'
      }
    },
    ...
  ]
}

If you haven’t a multi-site Drupal you can ignore domainsourceid field.¬†The nodetags lists some Tag names of a Many-to-many relationship not covered here.

All the other value are useful for the import:

  • nid: the original content id, used for pagination and retrieval
    Destination: parsing
  • nodepath:¬†content path
    Destination: Article.path
  • nodebody: content body
    Destination: Article.body
  • nodetype: type of the node
    Destination: parsing
  • nodetitle: title of the node
    Destination: Article.title
  • nodeauthor:¬†author of the content
    Destination: Article.author -> Author.alias

In the previous article you find how to make the View on Drupal (source) and now you have  rough idea of the field mapping. How to fetch the data from Django?

Management command and paged view

To start a one-time import you can write a custom management command for your Django application named project/app/management/commands/myimport.py.

from __future__ import unicode_literals
from django.core.management.base import BaseCommand, CommandError
from django.core.exceptions import ValidationError, MultipleObjectsReturned, ObjectDoesNotExist
import json, urllib
import urlparse
from shutil import copyfile
from django.conf import settings
from os import sep
from django.core.files.storage import default_storage
from django.utils.text import slugify
import requests
import grequests
import time
from md5 import md5

class Command(BaseCommand):
    help = 'Import data from Drupal 6 Json view'
    def add_arguments(self, parser):
        parser.add_argument('start', nargs=1, type=int)
        parser.add_argument('importtype', nargs=1)
        # Named (optional) arguments
        # Crawl
        parser.add_argument('--crawl',
            action='store_true',
            dest='crawl',
            default=False,
            help='Crawl data.')
    def handle(self, *args, **options):
        # process data
        pass

This management command can be launched with

python manage.py myimport 0 article --crawl

Where 0 is the item to start + 1, “article” is the type of content to import (e.g. the destination model) and –crawl is the import option. Let’s add the import logic to the Command.handle method:

def handle(self, *args, **options):
    try:
        assert options['crawl'] and options['importtype']
        # start to import or store data
        sid = int(options['start'].pop())
        reading = True
        while reading:
            importazioni = []
            articoli = []
            url = 'http://www.example.com/json-path-verylongkey?nid=%d' % (sid,)
            print url
            response = urllib.urlopen(url)
            data = json.loads(response.read())
            data = data['']
            # no data received, quit
            if not data:
                reading = False
                break
            for n, record in enumerate(data):
                sid = int(record['']['nid'])
                title = record['']['nodetitle']
                # continue to process data, row after row
                # ...

    except AssertionError:
        raise CommandError('Invalid import command')

This example will fetch /json-path-verylongkey starting from nid passed from the command + 1. Then, it will process the json row after row and keep in memory the id of the last item. When no content is available, the cycle will stop. It’s a common method and it’s lightweight on the source server because only one request at time are sent and then the response is processed. Anyway, this method can be also slow because we have to sum waiting time: (request 1 + response 1 + parse 1) + (request 2 + response 2 + parse 2) etc.

Multiple, asyncronous requests

We can speed up the retrieval by using grequests. You have to check what is the last element first by cloning the Drupal data source json view and showing only the last item, then fetching the id.

def handle(self, *args, **options):
    try:
        assert options['crawl'] and options['importtype']
        # start to import or store data
        sid = int(options['start'].pop())
        # find last node id to create an url list
        url = 'http://www.example.com/json-path-verylongkey-last-nid'
        response = requests.get(url, timeout = 50)
        r = response.json()
        last_nid = int(r[''].pop()['']['nid'])

You can then create a from-to range starting from the first element passed by command line to the last.

url_pattern = "http://www.example.com/json-path-verylongkey-last-nid?fromnid=%d&tonid=%d";
urls = []
per_page = 20
# e.g. [0, 20, 40, 60]
relements       = range(0, last_nid, per_page)
if relements[-1] < last_nid:
    relements.append(last_nid + 1)
for fromx, toy in zip(relements, relements[1:]):
    u = url_pattern % (fromx, toy)
    urls.append(u)

rs = (grequests.get(u) for u in self.urls)
# blocking request: stay here until the last response is received
async_responses = grequests.map(rs)
# all responses fetched

The per_page is the number of element per page specified on Drupal json view. Instead of a single nid parameter, fromnid and tonid are the parameter “greater than” and “less or equal than” specified in the Drupal view.

The core of the asyncronous, multiple requests is grequests.map(). It take a list of urls and then request them. The response will arrive in random order but the async_responses will be populated by all of them.

At that point you can treat the response list like before, parsing the response.json() of each element of the list.

With these hints you can now create JSON views within Drupal ready to be fetched and parsed in Django. In a next article I will cover the conversion between the data and Django using the Django ORM.

Guide to migrate a Drupal website to Django after the release of Drupal 8

I maintain a news website written in Drupal since 2007. It is a Drupal 6, before was a 5. I made many Drupal 7 installations in these years and I went to three Drupal local conventions. This is a guide on how to abandon Drupal if you already knows some basics of Django and Python.

Drupal on LAMP: lessons learned

  • PHP is for (not so) fast development¬†but¬†maintainability can be a pain.
  • Drupal try to overcome PHP limits, with mixed results.
  • Apache cannot stands heavy¬†traffic without an accelerator like Varnish and time-consuming ad-hoc configurations. If traffic increases, Apache cannot stand it at all.
  • Drupal¬†contrib modules are¬†a mix of high quality tools (like Webform or Views Datasource) and bad written¬†projects. The more module are enabled, the more the project¬†lose in maintainability. It is not so evident if you don’t see any other open source project.

This is not the only real truth, this is my experience in these 8 years. I feel a more confident Python programmer than PHP programmer having spent less than one-third of the years working on it. At the end of the article I cite a list of article written for programmers feeling the same uneasiness of mine working on PHP and Drupal after trying other tools.

Django experiences

In the last years with Drupal still paying most of my bills I used the Django MVC framework written in Python for three project: an e-mail application, a real estate catalog  and a custom-made CRM. One of this is a porting of something written in PHP on Drupal 5. In all of these three project I was very happy with the maintainability, clearness of the code and high-level, well written packages I found while exploring it like Tastypie and many python packages found on cake shop.

Even considering I’m the only developer of these, I haven’t experienced the frustration I feel on Drupal when trying to make something work as I design or trying to fix some code I write time ago. I know that a CMS is at higher level than a framework, simply some projects are not suited for Drupal and I found more comfortable with Python than PHP in these days.

At the time I write¬†Drupal 8 is out as Release Candidate. I made migrations from 5 to 6 and from 6 to 7 on some websites in the past. Migrating to a new major¬†it’s not a science, it’s a sort of mystical art. When the Drupal 8 will be out, Drupal 6 will be automatically unsupported after 3 months Drupal 8 is out as of Drupal announcement since only the current and previous version are supported, 8.x and 7.x when 8 is out. Keeping a Drupal 6 running after that term will be risky.

Choosing the stack

Back to the news website I maintain, the choice is between a platform I already know well and it proves stable and maintainable for small/one-person team and another I have to learn. Plus,¬†Django will be the natural choice to avoid the problems I’ve listed above and use the¬†solutions I used on past django projects exploring new tools in the meanwhile.

Here the choices I made:

I decided to use gunicorn because it’s very easy to run and maintain¬†for a django project and you haven’t to make wsgi run on nginx. Nginx is in front of gunicorn, serving static files and sending right requests to it. Memcached is used inside Django and it will store cached pages from views¬†on volatile memory avoiding to read from the database any time a page is requested. I try to avoid using Varnish even if is a very good tool because I want to keep the stack¬†as simple as I can and I’m confident Varnish and Memcache will speed up the website enough. Now is the time to rewrite the Drupal-hosted website into a Django application.

Write the E-R model

If you are here probably you have a running Drupal website you want to port to Django. Browse it like an user, and then open your Content types list to identify the Entities and the Relationships as of the E-R model suggests. If your website is running for a long time you probably want to redesign some parts, adding, removing or fusing entities into another.

Take my news website¬†for example. I have 15 content types + 12 vocabularies (27 entities) on Drupal. After rewriting the E-R I’ve 14 models (entities), including the core ones. On the database side it translates into a 199 tables for Drupal and 25 for Django¬†since it¬†usually make an entity property into a database column. I trash some entities and fuse 4 entities into one.

From entities to models: understanding relationships

When you establish a relation between your re-designed entities you can have N:1¬†relations, N:N relations and 1:1 relations. A Drupal node “Article” that accepts a single term for a vocabulary named “Cheese type” translates into a N:1 relationship between the model Article¬†(N)¬†and the¬†model¬†CheeseType (1).¬†It is a simple case since you can translate it into a ForeignKey¬†field on your model since Article will get a ForeignKey field named author referencing to the Author model.

from django.db import models
from tinymce import models as tinymce_models
# Authors
class Author(models.Model):
    alias       = models.CharField(max_length=100)
    name        = models.CharField(max_length=100, null=True, blank=True)
    surname     = models.CharField(max_length=100, null=True, blank=True)
# Articles
class Article(models.Model):
    author      = models.ForeignKey('Author')
    title       = models.CharField(max_length=250,null=False, blank=False)
    body        = tinymce_models.HTMLField(blank=True, default='')
# Attachments to an Article
class Attachment(models.Model):
    article       = models.ForeignKey('Article', blank=True, null=True)
    file          = models.FileField(upload_to='attachment_dir', max_length=255, blank=True, null=True)
    description   = models.TextField(null=True, blank=True)
    weight        = models.PositiveSmallIntegerField()

In the case of a list of attachments to Article, you have a 1:N relationship between the Article model (1) and the Attachment model (N). Since the relationship is reversed, in the usual Django admin interface you cannot see the attachments in the article as is since you have to create an Attachment and then choose an article from a dropdown where attach it to.

For this case, Django provides an handy administration interface called inline to include entities in reversed relationship. This approach fix by design something that in Drupal world costs a lot of effort, with dozen of modules like Field Collection or workaround like this I write of in the past and it keep aligned your E-R design with your models. Plus, a list of all Attachment are available for free.

Exporting the data from Drupal

JSON is a pretty good interchange format: very fast to encode and decode, very well supported. I’m fascinated with YAML format but since I’ve to export thousands of articles I need pure speed and solid import/export modules on both Django and Drupal side.

There are many export module in the Drupal world. I’m very fond of Views Datasource and here how I used it:

  1. Install Views Json (part of Views Datasource): it is available for Drupal 6 and 7 and very solid
  2. Create a new view with your published nodes with the JSON Data style
    1. Field output: Normal
    2. Without Plain text (you need HTML)
    3. Json data format: Simple
    4. Without Views API mode
    5. application/json as Mime type
    6. Remove all parent / children tag name so you will have only arrays and objects
  3. Choose a path for your view
  4. Limit the view to a large number of elements, e.g. 1000
  5. Sort by node id, ascendent
  6. Add an exposed filter “greater than” Nid with a custom Filter identifier (e.g. nid)
  7. Add any field you need to import and any filter you need to limit the results
  8. Avoid caching the view
  9. Limit the access to the view if you don’t want to expose sensible contents¬†(optional)
  10. Install a plugin like JsonView (chrome) or JsonView (firefox) to look at the data on your browser

You will get something like that:

{
  [
    {
      {nid: "30004",
      domainsourceid: "1",
      nodepath: "http://example.com/path/here",
      postdate: "2014-09-17T22:18:42+0200",
      nodebody: "HTML TEXT HERE",
      nodetype: "drupal type",
      nodetitle: "Title here",
      nodeauthor: "monty",
      nodetags: "Drupal, basketball, paintball"
      }
    },
    ...
  ]
}

Now you can reach the view appending ?nid=0 to your path. It means that any node with id greater than 0 will be listed. With nid=0 a max of 1000 elements are listed. To get other nodes you have simply to get the nid from the last record (e.g. 2478) and use it as value for the nid parameter obtaining something like http://example.com/myview?nid=2478.

Try it on your browser simulating what a procedure will do for you: check the response size and adapt the number of elements (#4) accordingly to avoid to overload your server, hit the timeout or simply storing too much data into the memory when parsing. When the view response is¬†empty you’ve listed all nodes matching your filters and the parsing is complete.

In this example I’ve talked about nodes but you can do the same with files, using fid as id to pass as parameter and to sort your rows. In the case of files you have to move the files as well but it’s pretty simple to import these on a custom model on Django as you will see.

Importing data to Django

Django comes with some nice export (dumpdata)¬†¬†and import¬†(loaddata) commands. I’ve used a lot the YAML format to migrate and backup data from models but Json and SQL are other supported formats you can try. However in this migration I choose¬†custom admin command to do the job. It’s fast: in less than 10 minutes the procedure¬†imported 15k+ articles writing on a custom model some logging information on both error and¬†success.

All the import code in my case, comments and import included, is about 300 lines of python code. The core of the import function for nodes willing to become Articles is that:

import json, urllib
# ...
sid = int(options['start'].pop())
reading = True
while reading:
    url = "http://mydrupalwebsite.example.com/myview?nid=%d" % (sid,)
    print url
    response = urllib.urlopen(url)
    data = json.loads(response.read())
    data = data['']
    # no data received, empty view result, quit
    if not data:
        reading = False
        break
    for n, record in enumerate(data):
        sid = int(record['']['nid'])
        # ... do something with data ...

In this cycle, sid is the start argument passed to the admin command via command line. Next, sid will be set to the last read record so, when record finishes, a new request to myview starting from the last read element will be made.

All input and output is UTF-8 in my case. JSON View quotes strings and you have to decode them before saving in Django:

from myapp.models import Article
import HTMLParser
hp = HTMLParser.HTMLParser()
authors = Author.objects.all()
...
for n, record in enumerate(data):
    try:
        art = Article(
            title = hp.unescape(record['']['nodetitle']),
            body = record['']['nodebody'],
            author = authors.get(alias=record['']['nodeauthor'])
        )
        # run the same validation of an admin interface submit
        art.full_clean()
        art.save()
    except ValidationError as e:
      # cannot save the element
      # inside e all the error data you can save into
      # a custom log model or print to screen
    except:
      # any other exception
      pass

On line 9 a new article is declared. The title in Json source is named nodetitle. On line 10 the title from json is unescaped and assigned to title CharField of Article. The nodebody  is set as it is since the destination field is a TextField with HTML. On line 11 username nodeauthor from Json is used as key to associate the already imported user to the ForeignKey field author, where username is saved as Author.alias.

Conclusion

Here the very basics on how to prepare a migration from Django to Drupal using Views Datasource module and a custom admin command. I described why I choose Django after years of Drupal development for this migration suggesting some tools to do the job and introducing some basic concepts for Drupal developer who wants to try Django.

I’ve read about Drupal enthusiasts that suffers the same uneasiness of mine after long-time Drupal / PHP development. In their words I found some confort in my day programming job and a lot of inspiration.

Epilogue

Here the download time graph from Google Search Console after some months:
downloadtime

You can clearly see the results in speed, expressed in milliseconds, between 2015 (old Drupal 6 platform) and 2016 (new Django platform).

Finally I quit my Drupal job and now I’m programming mostly with Python.

Django and Drupal integration using drush via SSH

Some months ago I talked about how to achieve a unified login from Django to Drupal using drush. The basic assumption was that both Drupal and Django are on the same server. What if the two components are on different servers?

Paramiko is a SSH2 protocol library aimed to provide simple classes to make SSH connection. Let’s see how the code to call drush on command line changes.

Prerequisites:

  • paramiko
  • on your app settings.py add:
  • DRUPAL_SERVER_SSH_HOST     = '0.0.0.0' # Your host here
    DRUPAL_SERVER_SSH_USERNAME = 'YourRemoteServerUserHere'
    DRUPAL_SERVER_SSH_PASSWORD = 'YourRemoteServerPasswordHere'

    And then:

    assert request.user.drupal_id > 0
    # user id to log in
    drupal_id = str(request.user.drupal_id)
    output = ""
    try:
     # a list with command as first element and arguments following
     get_password_recovery_url = ["drush", "-r", settings.DRUPAL_SITE_PATH, "-l", settings.DRUPAL_SITE_NAME, "user-login", drupal_id]
     # via ssh http://stackoverflow.com/a/3586168/892951
     ssh = paramiko.SSHClient()
     # add to known_host the remote server key if it's not already stored
     # @see http://jessenoller.com/blog/2009/02/05/ssh-programming-with-paramiko-completely-different
     ssh.set_missing_host_key_policy(paramiko.AutoAddPolicy())
     ssh.connect(settings.DRUPAL_SERVER_SSH_HOST, username=settings.DRUPAL_SERVER_SSH_USERNAME, password=settings.DRUPAL_SERVER_SSH_PASSWORD)
     ssh_stdin, output, ssh_stderr = ssh.exec_command(" ".join(get_password_recovery_url))
     output_lines = output.read().splitlines()
     # taking only the first line of the output:
     # e.g. 'http://example.com.it/user/reset/16/1369986816/67k7ReHi97FdtRfdrrXGqqesyz6FXyy7T8jqHiXxsrY/login'
    except:
     # @todo additional statements here
     pass
    finally:
     if ssh:
      ssh.close()
    
    if output_lines:
    drupal_login_url = output_lines[0].replace("http://example.com/", "http://%s/" % settings.DRUPAL_SITE_URL).strip()
    
    destination = "%s?destination=%s" % (drupal_login_url, settings.DRUPAL_LOGIN_DESTINATION)
     return redirect(destination)
    else:
     return HttpResponse('
    <h1>Wrong request</h1>
    ')
    

    This is the same code of the previous howto, with the difference that drush now is running on a different server of django. You can use the same method to do anything you have to with drush, any time you call this piece of code an SSH connection is opened.

    See also:

Django development on Virtualbox: step by step setup

I had a bad morning trying to repair my Cygwin installation from a virtualenv mess. It’s time to get a Debian and install it on a Virtualbox for my new django project!

  • Windows: host
  • Debian: guest

Choosing the distro: what I want

  • Python 2.6
  • Django 1.4
  • Apache + Mysql

I’m a Debian fan from years so I go to the Debian website and download Wheezy netinst¬†iso (32 bit, since I’m on a 32 bit OS and I want to use more core): wheezy met all the requirements above.

I already have a Virtualbox, so what I do is to add a new virtual disk and to add the new Wheezy netinst iso on CD/DVD images. Then I create a new Debian machine (32 bit) with two cores. I choose the iso image to be mounted on startup so the Debian setup process will start on boot.

As network device, I choose the Bridge option, so I can access the machine later from my windows host.

Installing the system

When you turn your machine on, many choices will be prompted to you. I install the webserver (apache) from the list, removed SQL server and print server and then leave desktop selected and the other default values. After some minutes Debian is installed and I can log in with the credential I have specified during installation.

Use WORKGROUP as network name if you’re running a Windows host when asked.

Install django packages

Under the Application menu, find the Debian package management tools¬†to install what you want. As the requirements I’ve listeded above I search and install those packages:

  • python-django (1.4.1-2)
  • libapache2-mod-uwsgi
  • libapache2-mod-wsgi
  • mysql-server
  • samba

Later you can install more useful packages like virtualenv and phpmyadmin.

After you’ve installed those packages, you can do some test.¬†Open a shell (Accessories > Terminal) and then type these commands:

What version of python I’m running?

$ python

Python 2.7.3rc2 (default, Apr 22 2012, 22:35:38)
[GCC 4.6.3] on linux2
Type “help”, “copyright”, “credits” or “license” for more information.
>>>

So I’ve python 2.7. Good!

>>> import django
>>> django.VERSION
(1, 4, 1, ‘final’, 0)

And I’ve Django 1.4.1.

Share your code to the Windows network (workgroup)

Now I want to read the code from one machine to another. I choose Samba server to read and write files from the virtual machine to windows and back. It will be useful since I’ve a complete Eclipse + pydev¬†IDE on windows and I love work with it.

I open a Root terminal and type:

# ifconfig

If you choosed the Bridge network interface on installation, you will got something like this:

eth0 Link encap:Ethernet HWaddr ??????
inet addr:192.168.0.104 Bcast:192.168.0.255 Mask:255.255.255.0
inet6 addr: ???????????/64 Scope:Link
UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1
RX packets:49280 errors:0 dropped:0 overruns:0 frame:0
TX packets:19777 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:1000
RX bytes:45400047 (43.2 MiB) TX bytes:1887849 (1.8 MiB)
Interrupt:19 Base address:0xd020

The address in bold (192.168.0.104) is the local network address of my virtual machine. If I just type this address in the Chrome browser it’s running on Windows (host) I got the “It works!” from Apache on the virtual machine. If you can’t see nothing, left click on the network icon on the bottom of your virtualbox windows > click on the menu voice and then choose the Bridge option. Then redo the ifconfig as above.

Samba tuning

Create a directory to store your django code (inside current user home folder). Open the terminal as normal user:

$ cd
$ mkdir my-django-code

Then share this folder with samba. To do this, let’s create a new user without a password:

adduser guest –home=/home/public –shell=/bin/false –disabled-password

Then add these lines to /etc/samba/smb.conf on “## Authentication ##” section:

security = share
guest_account = guest
invalid_users = root

obey pam restrictions = yes

And then after the [cdrom] commented text:

[my-django-code]
comment=Django-code
read only = no
locking = no
path = /home/myuser/my-django-code
guest ok = yes
force user = myuser

Where myuser is my (normal) user name. The lines above tell something like this to samba:

  • Let a guest user access without a password
  • …to the path¬†/home/myuser/my-django-code
  • …”masquerading” like myuser

The “masquerade” thing is all about having the right to write files created from myuser from the guest user on the host.

When i browse my Workgroup on windows, I found the machine name I choose during installation and inside I found the my-django-code directory. I try to read and write files from the host (Windows) and from the guest (Debian) and it’s all ok.

Django, finally!

If you’re starting to develop on django, so this howto for beginners will help you a lot. Since I’ve installed the python-django package from Debian, to start a project is simple as typing this:

$ cd
$ cd my-django-code
$ django-admin startproject django_unchained
$ cd django_unchained
$ python manage.py runserver 192.168.0.104:8000

Where 192.168.0.104 is the virtual machine local network address from above and 8000 the port of the django testing webserver.

I type:

http://192.168.0.104:8000

on Chrome (host: Windows) and I get the hello page from Django. Perfect!

Then, I can just follow the django howto to do the right things during the creation of my new app django_unchained!

You can also explore the must-have list of tools and sites for Python developers.