Django apps and ORM Beyond the basics [Meetup hosted by Prodeers.com]
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This document outlines a meetup focusing on Django, a high-level Python web framework that facilitates rapid development and clean design. It discusses key components of Django such as its architecture, models, views, templates, and how to set up a Django environment. Additionally, it highlights the advantages of using Django, popular sites built with it, and provides references for further learning.
Django apps and ORM Beyond the basics [Meetup hosted by Prodeers.com]
- 1. DJANGO APPS AND ORM PRODUCT VALLEY MEETUP GROUP BANGALORE (A PRODEERS CHAPTER) - BY UDIT GANGWANI
- 2. ABOUT ME I WEAR MULTIPLE HATS SOFTWARE DEVELOPER PRODUCT MANAGER ENTREPRENEUR I LOVE TO TRAVEL MY FRIENDS CALL ME PIZZA MANIAC
- 3. WHAT WILL WE LEARN TODAY INTRODUCTION TO DJANGO HOW TO GET STARTED WITH DJANGO COMPONENTS OF DJANGO FRAMEWORK DJANGO MODELS, MODEL MANAGERS AND QUERY SETS HOW DO DJANGO MODELS WORK
- 4. WHAT IS DJANGO ? Django is a high-level Python Web framework that encourages rapid development and clean, pragmatic design. Built by experienced developers, it takes care of much of the hassle of Web development, so you can focus on writing your app without needing to reinvent the wheel. -- https://www.djangoproject.com/
- 5. WHY DJANGO ? • Incredible programming language (Python) • Perfect ORM for handling database • Offers great control (Explicit is better than implicit) • Django Admin GUI • Simple and smaller footprint to get started • Very big & active community • Lots of Django packages for almost every functionality • Support for large variants of Databases • Django REST Framework
- 6. MTV ARCHITECTURE Django follows MTV architecture: M – Model • app/models.py V – View • app/views.py T – Templates • app/templates/*.html It is analogous to MVC architecture. View in MVC corresponds to Template in MTV Controller in MVC corresponds to View in MTV
- 7. POPULAR SITES BUILT WITH DJANGO • Pinterest • Instagram • Discus • Spotify • Washington Post • Firefox • NASA • BitBucket • Prezi • EventBrite
- 8. DJANGO SETUP AND A DEMO
- 9. ENVIRONMENT SETUP • Standard Environment • Common environment and set of packages for each project on your system • Virtual Environment • Isolated environment for each Django project • No limits on the number of environments • Can have different python version for each project • Using virtualenv or pyenv
- 10. STEPS TO SETUP VIRTUAL ENVIRONMENT • pip install virtualenv • virtualenv .app • source appbinactivate
- 11. GETTING STARTED WITH DJANGO • Install Django using pip • Create a project using django-admin • Create your database • Configure DB settings in settings.py • Define your models • Add external modules • Write your Templates • Define your Urls • Write your Views and bind them to Urls • Test application • Deploy application using NginX or Apache
- 12. DJANGO PROJECT STRUCTURE • Each Django app is a Python Package • Each app contains one or more Python modules (files of python code) • To form a package every app directory must contain an __init__.py file
- 15. URL’S DISPATCHER/ROUTING • Django determines the root URLconf module to use • Django loads the Python module and looks for the variable urlpatterns • Django runs through each pattern and stops at the one which matches • Once the regex matches, Django calls the given View
- 16. VIEWS • A Django view is a callable which takes a request and returns a response
- 17. MODELS & MODEL FIELDS • Each model maps to a single database table. • Each model is a Python class that subclasses django.db.models.Model • Each attribute of the model represents a database field
- 18. TEMPLATES • A template contains the static parts of the desired HTML output as well as some special syntax describing how dynamic content will be inserted
- 19. MIDDLEWARES • Middleware is a framework of hooks into Django’s request/response processing. It’s a light, low-level “plugin” system for globally altering Django’s input or output.
- 20. DJANGO MODELS
- 21. MIGRATIONS • Migrations are Django’s way of propagating changes you make to your models (adding a field, deleting a model, etc.) into your database schema. • They’re designed to be mostly automatic Thereareseveralcommandswhichyouwilluse tointeractwithmigrations: •migrate,whichisresponsibleforapplyingmigrations,aswellas unapplyingandlistingtheirstatus. •makemigrations,whichisresponsibleforcreatingnewmigrationsbasedonthechangesyouhavemadetoyourmodels. •sqlmigrate,whichdisplaystheSQLstatementsforamigration. •showmigrations,whichlistsaproject’smigrations.
- 22. MODEL RELATIONSHIPS Many to One Relationships Many to Many Relationships One to One Relationships
- 23. MODEL QUERIES • Creating Objects • Retrieving Objects • Create query set objects using your model manager. A query set represents the collection of objects from database • Query sets are lazy • Retrieving specific objects using filters
- 24. MODEL QUERIES ON RELATED OBJECTS One to Many Field One to One Many Reverse lookup Many to Many Field One to One Field
- 25. MANAGERS • A Manager is the interface through which database query operations are provided to Django models. At least one Manager exists for every model in a Django application. • Adding extra Manager methods is the preferred way to add “table-level” functionality to your models. (For “row-level” functionality – i.e., functions that act on a single instance of a model object – use Model methods, not custom Manager methods.)
- 26. MANAGERS EXAMPLE
- 27. QUERY SETS • Internally, a QuerySet can be constructed, filtered, sliced, and generally passed around without actually hitting the database. No database activity actually occurs until you do something to evaluate the queryset. • Important methods that return new Query set • filter(), exclude(), annotate(), order_by(), reverse(), distinct(), values(), all() • Important methods that do not return Query set • get(), create(), update(), aggregate(), iterator(), count()
- 28. Q OBJECTS • A Q object (django.db.models.Q) is an object used to encapsulate a collection of keyword arguments. It is used to execute more complex queries (for example, queries with OR statements)
- 29. AGGREGATION Aggregation for entire table Aggregation for each item in table
- 30. HOW DO DJANGO MODELS WORK ?
- 31. HOW DO MODELS WORK - METACLASSES Lets understand what goes on from the time a model is imported until an instance is created by the user. Lets look at an example model
- 32. HOW DO MODELS WORK - METACLASSES So ModelBase.__new__ is called to create this new Example class. It is important to realise that we are creating the class object here, not an instance of it The Model class (see base.py) has a __metaclass__ attribute that defines ModelBase (also in base.py) as the class to use for creating new classes. The __new__ method is required to return a class object that can then be instantiated (by calling Example() in our case). A new class object with the Example name is created in the right module namespace. A _meta attribute is added to hold all of the field validation, retrieval and saving machinery
- 33. HOW DO MODELS WORK - METACLASSES Each attribute is then added to the new class object. Putting this in the context of our example, the static and __unicode__ attributes would be added normally to the class as a string object and unbound method, respectively. In case of Field, it does not add the new attribute to the class we are creating (Example). Instead it adds itself to the Example._meta class, ending up in the Example._meta.fields list The ModelBase._prepare method is called. This sets up a few model methods that might be required depending on other options you have selected and adds a primary key field if one has not been explicitly declared. The registration is done right at the end of the ModelBase.__new__ method. The register_models() function in loaders.py
- 34. REFERENCES • Django Orm at Django under the hood: https://www.youtube.com/watch?v=CGF-0csOjPw • Django Topics: https://docs.djangoproject.com/en/1.9/topics/ • What is a MetaClass in Python: http://stackoverflow.com/questions/100003/what-is-a- metaclass-in-python • How do Django Models work: • http://stackoverflow.com/questions/12006267/how-do-django-models-work • https://code.djangoproject.com/wiki/DevModelCreation • Django Cookbook: https://code.djangoproject.com/wiki/CookBook • Python3 Cookbook: http://python3- cookbook.readthedocs.io/zh_CN/latest/c09/p18_define_classes_programmatically.html
- 35. REFERENCES • Try Django Blog Project: • https://github.com/codingforentrepreneurs/try-django-19 • https://www.codingforentrepreneurs.com/projects/try-django-19/ • Django Models and Migrations: • http://www.webforefront.com/django/setupdjangomodels.html • Making Django Queries : • https://docs.djangoproject.com/en/1.9/topics/db/queries/ • Understanding Django Model Managers and QuerySets: • https://docs.djangoproject.com/en/1.9/ref/models/querysets/ • https://docs.djangoproject.com/en/1.9/topics/db/managers/
- 36. THANK YOU