Code reviews and tips for better implementation of Django backends

1. Django/ Python Development

2. About me
Senior Software Engineer/
Team Lead

3. Why Django?
• Easy to Use
• It’s fast and simple
• Excellent Documentation
• It’s secure
• It suits any web application project

4. Disadvantages
Monolithic
Not suited for small-scale
projects
No default support for
WebSockets.

5. Framework features:
Templating Engine
Object-relational mapper (ORM)
URL routing
Authentication
Internationalization.
Admin Panel
A wide variety of ready-to-use libraries

6. EventBrite
Bitbucket
Pinterest
Instagram
The Washington Post

7. Schedule a job
(Redis Queue) is a simple Python library for queueing jobs
and processing them in the background with workers. It is
backed by Redis and it is designed to have a low barrier to
entry. It should be integrated in your web stack easily.
Installations:
Pip install rq-scheduler

8. Schedule a job
• Example

9. Questions
TIPS

10. Tips for better programming
• Source <venv>
• Pip install –r requirements.txt
• Python manage.py migrate
• Python manage.py runserver
Have a
quickstart
script

11. Tips for better programming
Write
Tests
Update
Tests
Add
more
Tests

12. Use environment variables for
settings

13. Handling Settings for Multiple
Environments

14. Use Continuous Integration

15. Discussions

16. Explain user object in the Django
admin system with its 3 flags?

17. Complex Queries!
How can you handle Oring
operations in the queryset
Example:
Fetching created items today and yesterday:
items= Item.objects.filter
(models.Q(created_at=today) |
models.Q(created_at=yesterday) )

18. Optimize Database Calls with
Prefetch Related and Select Related
Usage:
prefetch related:
fetch a reverse foreign key or a many to many relationship.
select related:
when we want to fetch a foreign key or a one to one
relationship.

19. Optimize Database Calls with
Prefetch Related and Select Related
Usage:
prefetch related:
fetch a reverse foreign key or a many to many relationship.
select related:
when we want to fetch a foreign key or a one to one
relationship.

20. Annotate Querysets to Fetch
Specific Values
Annotating a queryset enables you to add attributes to
each object in the queryset. Annotations can be a
reference to a value on the model or related model or an
expression such as a sum or count.
Example:
Appointment.objects.filter(status=..).annotate(appointment
_length=F("end_time") - F("start_time"))

21. Annotate Querysets to Fetch
Specific Values
Annotating a queryset enables you to add attributes to
each object in the queryset. Annotations can be a
reference to a value on the model or related model or an
expression such as a sum or count.
Example:
Appointment.objects.filter(status=..).annotate(appointment
_length=F("end_time") - F("start_time"))

22. Code Review (1)
https://github.com/Jd2020D/food2eat
Jehad Al-Terawi
Yasmeen Muhtaseb
Mahmoud Khateeb
Does this line of code have any issue?

23. Code Review (2)
https://github.com/Jd2020D/food2eat
What if more than one item have the same name?
Do we have any other mechanism to check the item?
What type of exception raised here?

24. Code Review (3)
https://github.com/Jd2020D/food2eat
Why you are getting the last order only?
Optimization!
Return list of Queryset
Meal.objects.filter(meal__id=meal_id,items__order__user__id=?).values()
Return list of ids
Meal.objects.filter(meal__id=meal_id). values_list(id', flat=True)()

25. Code Review (4)
https://github.com/Jd2020D/food2eat
Duplication!!!!!!!!!
- Base model (abstract)
- django-model-utils
- TimeStampFields, Softdelete, Status, Tracker, ..

26. Code Review (5)

27. To-Do
Is name field required?
How we can make it optional?
We need to force different title for each book?

28. TBD
Realtime Communication
What is new in Django 3
Deployment

30. Thank You