django-prefetch 0.1.0

Installation guide

Install it:

pip install django-prefetch

Use it as your model’s default manager (or as a base class if you have custom manager).

Example

Here’s a rather elaborate example with a fallback on regular 1+n queries (if you don’t call prefetch on the queryset):

from django.db import models
from prefetch import PrefetchManager, Prefetcher

class Author(models.Model):
    name = models.CharField(max_length=100)

    objects = PrefetchManager(
        books = Prefetcher(
            filter = lambda ids: Book.objects.filter(author__in=ids),
            reverse_mapper = lambda book: [book.author_id],
            decorator = lambda author, books=(): setattr(author, 'prefetched_books', books)
        ),
        latest_book = Prefetcher(
            filter = lambda ids: Book.objects.filter(author__in=ids),
            reverse_mapper = lambda book: [book.author_id],
            decorator = lambda author, books=(): setattr(
                author,
                'prefetched_latest_book',
                max(books, lambda book: book.created)
            )
        )
    )

    @property
    def books(self):
        if hasattr(self, 'prefetched_books'):
            return self.prefetched_books
        else:
            return self.book_set.all()

    @property
    def latest_book(self):
        if hasattr(self, 'prefetched_latest_book'):
            return self.prefetched_latest_book
        else:
            return self.book_set.latest()

class Book(models.Model):
    class Meta:
        get_latest_by = 'created'

    name = models.CharField(max_length=100)
    created = models.DateTimeField(auto_now_add=True)
    author = models.ForeignKey(Author)

Use it like this:

for a in Author.objects.prefetch('books', 'latest_book'):
    print a.books
    print a.latest_book

Requirements

The project has been tested on Django 1.1, 1.2, 1.3, 1.4 and trunk with Python 2.6 and 2.7.

TODO

• document collect option of Prefetcher

• create tests covering custom collect and mapper