Learn Python Coding on Telegram: “• Fetch related ForeignKey objects in the same q…”

• Fetch related ForeignKey objects in the same query.

entries = Entry.objects.select_related('author').all()

• Fetch related ManyToManyField objects in a separate efficient query.

entries = Entry.objects.prefetch_related('tags').all()

• Load only specific model fields.

entries = Entry.objects.only('headline')

• Defer loading of specific model fields.

entries = Entry.objects.defer('body_text')

• Execute raw, unmanaged SQL.

authors = Author.objects.raw('SELECT * FROM myapp_author')

• Get results as a list of tuples.

Entry.objects.values_list('headline', 'pub_date')

XV. Transactions

• Import the transaction module.

from django.db import transaction

• Run a block of code within a database transaction.

with transaction.atomic():
    # All database operations here are either committed together or rolled back.
    author.save()
    entry.save()

XVI. Managers & Model Methods

• Create a custom Manager for common queries.

class PublishedEntryManager(models.Manager):
    def get_queryset(self):
        return super().get_queryset().filter(status='published')

• Add a custom method to a QuerySet via its Manager.

Entry.objects.get_queryset().by_author("John Doe")

• Add a custom method to a model for object-specific logic.

class Entry(models.Model):
    #...
    def is_recent(self):
        return self.pub_date > timezone.now() - timedelta(days=1)

#Python #Django #ORM #Database #Backend

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By: @DataScience4 ✨