https://developer.mozilla.org/en-US/docs/Learn/Server-side/Django

#django #tutorial #mozilla

https://books.agiliq.com/projects/django-orm-cookbook/en/latest/index.html

#django #orm #cookbook #django_orm

How to find the query associated with a queryset in Django ORM?

Sometime you want to know how a Django ORM makes our queries execute or what is the corresponding SQL of the code you are writing. This is very strightforward. Youn can get str of any queryset.query to get the sql.

You have a model called Event. For getting all records, you will write something like Event.objects.all(), then do str(queryset.query)

>>> queryset = Event.objects.all()
>>> str(queryset.query)
SELECT "events_event"."id", "events_event"."epic_id",
    "events_event"."details", "events_event"."years_ago"
    FROM "events_event"

Example 2:

>>> queryset = Event.objects.filter(years_ago__gt=5)
>>> str(queryset.query)
SELECT "events_event"."id", "events_event"."epic_id", "events_event"."details",
"events_event"."years_ago" FROM "events_event"
WHERE "events_event"."years_ago" > 5

#python #django #orm

https://www.youtube.com/watch?v=XMu0T6L2KRQ&list=PLEsfXFp6DpzTOcOVdZF-th7BS_GYGguAS

#python #django #rest

In Django unittests you can use fixtures in order to create dummy data. To create fixtures you can use django dumpdata command to dump a specific data:

python3 manage.py dumpdata --indent 4 YOUR_APP.YOUR_TABLE > output_data.json

This is how you can dump data and use it as your data backend for unittests.

#django #python3 #dumpdata #unittest

What does select_related do in Django?

select_related does a join in case needed on the DB side and reduce query counts. Let's look at an example:

# Hits the database.
e = Entry.objects.get(id=5)

# Hits the database again to get the related Blog object.
b = e.blog

In the above code 2 queries are issued in DB side. First it gets Entry record and then blog is fetched from DB when e.blog is called. And here’s select_related lookup:

# Hits the database.
e = Entry.objects.select_related('blog').get(id=5)

# Doesn't hit the database, because e.blog has been prepopulated
# in the previous query.
b = e.blog

You can follow foreign keys in a similar way to querying them. If you have the following models:

from django.db import models

class City(models.Model):
    # ...
    pass

class Person(models.Model):
    # ...
    hometown = models.ForeignKey(
        City,
        on_delete=models.SET_NULL,
        blank=True,
        null=True,
    )

class Book(models.Model):
    # ...
    author = models.ForeignKey(Person, on_delete=models.CASCADE)

Then a call to Book.objects.select_related('author__hometown').get(id=4) will cache the related Person and the related City:

# Hits the database with joins to the author and hometown tables.
b = Book.objects.select_related('author__hometown').get(id=4)
p = b.author         # Doesn't hit the database.
c = p.hometown       # Doesn't hit the database.

# Without select_related()...
b = Book.objects.get(id=4)  # Hits the database.
p = b.author         # Hits the database.
c = p.hometown       # Hits the database.

#python #django #select_related #join #database #models