Initial checkin

.gitignore

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+ve
+demo/data.db
+

README.txt

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+django_lazymap
+==============
+
+Allows you to register a transforming map function with a Django QuerySet 
+that will be executed only when the QuerySet itself has been evaluated.
+
+This allows you to build optimisations like "fetch all tags for these 10 rows"
+while still benefiting from Django's lazy QuerySet evaluation.
+
+For example:
+
+    def lookup_tags(item_qs):
+        item_pks = [item.pk for item in item_qs]
+        m2mfield = Item._meta.get_field_by_name('tags')[0]
+        tags_for_item = Tag.objects.filter(
+            item__in = item_pks
+        ).extra(select = {
+            'item_id': '%s.%s' % (
+                m2mfield.m2m_db_table(), m2mfield.m2m_column_name()
+            )
+        })
+        tag_dict = {}
+        for tag in tags_for_item:
+            tag_dict.setdefault(tag.item_id, []).append(tag)
+        for item in item_qs:
+            item.fetched_tags = tag_dict.get(item.pk, [])
+
+    qs = Item.objects.filter(name__contains = 'e').lazymap(lookup_tags)
+
+    for item in qs:
+        print item, item.fetched_tags
+
+Prints:
+
+    Winter comes to Ogglesbrook [<sledging>, <snow>, <winter>, <skating>]
+    Summer now [<skating>, <sunny>]
+
+But only executes two SQL queries - one to fetch the items, and one to fetch ALL of the tags for those items.
+
+Since the lazymap function can transform an evaluated QuerySet, it 
+doesn't need to make extra database calls at all - it should work well for 
+things like cache.multi_get() too.
+
+Inspired by http://github.com/lilspikey/django-batch-select/

demo/demo_models/admin.py

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+from models import Tag, Item
+from django.contrib import admin
+
+admin.site.register(Tag)
+admin.site.register(Item)

demo/demo_models/models.py

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+from django.db import models
+from django_lazymap import LazyMapManager
+
+class Tag(models.Model):
+    name = models.CharField(max_length = 255)
+
+    def __unicode__(self):
+        return self.name
+
+class Item(models.Model):
+    name = models.CharField(max_length = 255)
+    tags = models.ManyToManyField(Tag)
+
+    objects = LazyMapManager()
+
+    def __unicode__(self):
+        return self.name

demo/demo_models/tests.py

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+"""
+This file demonstrates two different styles of tests (one doctest and one
+unittest). These will both pass when you run "manage.py test".
+
+Replace these with more appropriate tests for your application.
+"""
+
+from django.test import TestCase
+
+class SimpleTest(TestCase):
+    def test_basic_addition(self):
+        """
+        Tests that 1 + 1 always equals 2.
+        """
+        self.failUnlessEqual(1 + 1, 2)
+
+__test__ = {"doctest": """
+Another way to test that 1 + 1 is equal to 2.
+
+>>> 1 + 1 == 2
+True
+"""}
+

demo/demo_models/views.py

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+# Create your views here.

demo/manage.py

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+#!/usr/bin/env python
+from django.core.management import execute_manager
+try:
+    import settings # Assumed to be in the same directory.
+except ImportError:
+    import sys
+    sys.stderr.write("Error: Can't find the file 'settings.py' in the directory containing %r. It appears you've customized things.\nYou'll have to run django-admin.py, passing it your settings module.\n(If the file settings.py does indeed exist, it's causing an ImportError somehow.)\n" % __file__)
+    sys.exit(1)
+
+if __name__ == "__main__":
+    execute_manager(settings)

demo/settings.py

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+# Django settings for demo project.
+
+DEBUG = True
+TEMPLATE_DEBUG = DEBUG
+
+ADMINS = (
+    # ('Your Name', '[email protected]'),
+)
+
+MANAGERS = ADMINS
+
+DATABASE_ENGINE = 'sqlite3'           # 'postgresql_psycopg2', 'postgresql', 'mysql', 'sqlite3' or 'oracle'.
+DATABASE_NAME = 'data.db'             # Or path to database file if using sqlite3.
+DATABASE_USER = ''             # Not used with sqlite3.
+DATABASE_PASSWORD = ''         # Not used with sqlite3.
+DATABASE_HOST = ''             # Set to empty string for localhost. Not used with sqlite3.
+DATABASE_PORT = ''             # Set to empty string for default. Not used with sqlite3.
+
+# Local time zone for this installation. Choices can be found here:
+# http://en.wikipedia.org/wiki/List_of_tz_zones_by_name
+# although not all choices may be available on all operating systems.
+# If running in a Windows environment this must be set to the same as your
+# system time zone.
+TIME_ZONE = 'America/Chicago'
+
+# Language code for this installation. All choices can be found here:
+# http://www.i18nguy.com/unicode/language-identifiers.html
+LANGUAGE_CODE = 'en-us'
+
+SITE_ID = 1
+
+# If you set this to False, Django will make some optimizations so as not
+# to load the internationalization machinery.
+USE_I18N = True
+
+# Absolute path to the directory that holds media.
+# Example: "/home/media/media.lawrence.com/"
+MEDIA_ROOT = ''
+
+# URL that handles the media served from MEDIA_ROOT. Make sure to use a
+# trailing slash if there is a path component (optional in other cases).
+# Examples: "http://media.lawrence.com", "http://example.com/media/"
+MEDIA_URL = ''
+
+# URL prefix for admin media -- CSS, JavaScript and images. Make sure to use a
+# trailing slash.
+# Examples: "http://foo.com/media/", "/media/".
+ADMIN_MEDIA_PREFIX = '/media/'
+
+# Make this unique, and don't share it with anybody.
+SECRET_KEY = 'hea-c%x=u^&2bypgp81_+tfmxkt3l-ni-3$(yml%d=!@9&+u2x'
+
+# List of callables that know how to import templates from various sources.
+TEMPLATE_LOADERS = (
+    'django.template.loaders.filesystem.load_template_source',
+    'django.template.loaders.app_directories.load_template_source',
+#     'django.template.loaders.eggs.load_template_source',
+)
+
+MIDDLEWARE_CLASSES = (
+    'django.middleware.common.CommonMiddleware',
+    'django.contrib.sessions.middleware.SessionMiddleware',
+    'django.contrib.auth.middleware.AuthenticationMiddleware',
+)
+
+ROOT_URLCONF = 'demo.urls'
+
+TEMPLATE_DIRS = (
+    # Put strings here, like "/home/html/django_templates" or "C:/www/django/templates".
+    # Always use forward slashes, even on Windows.
+    # Don't forget to use absolute paths, not relative paths.
+)
+
+INSTALLED_APPS = (
+    'django.contrib.auth',
+    'django.contrib.contenttypes',
+    'django.contrib.sessions',
+    'django.contrib.sites',
+    'django.contrib.admin',
+    'demo_models',
+)

demo/urls.py

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+from django.conf.urls.defaults import *
+from django.contrib import admin
+from django.http import HttpResponse
+from django.db import connection
+
+from demo_models.models import Item, Tag
+
+from pprint import pformat
+
+admin.autodiscover()
+
+def example(request):
+    def lookup_tags(item_qs):
+        item_pks = [item.pk for item in item_qs]
+        m2mfield = Item._meta.get_field_by_name('tags')[0]
+        tags_for_item = Tag.objects.filter(
+            item__in = item_pks
+        ).extra(select = {
+            'item_id': '%s.%s' % (
+                m2mfield.m2m_db_table(), m2mfield.m2m_column_name()
+            )
+        })
+        tag_dict = {}
+        for tag in tags_for_item:
+            tag_dict.setdefault(tag.item_id, []).append(tag)
+        for item in item_qs:
+            item.fetched_tags = tag_dict.get(item.pk, [])
+
+    qs = Item.objects.all().lazymap(lookup_tags)
+
+    s = []
+
+    for item in qs:
+        s.append('%s: %s' % (item, [t.name for t in item.fetched_tags]))
+
+    return HttpResponse(
+        '<br>'.join(s) + '<pre>%s</body></html>' % pformat(connection.queries)
+    )
+
+urlpatterns = patterns('',
+    (r'^$', example),
+    (r'^admin/', include(admin.site.urls)),
+)

django_lazymap/__init__.py

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+from django.db import models
+
+class LazyMapQuerySet(models.query.QuerySet):
+    def __init__(self, *args, **kwargs):
+        super(LazyMapQuerySet, self).__init__(*args, **kwargs)
+        self._lazymap_fns = []
+
+    def lazymap(self, fn):
+        self._lazymap_fns.append(fn)
+        return self
+
+    def iterator(self):
+        result_iter = super(LazyMapQuerySet, self).iterator()
+        if self._lazymap_fns:
+            results = list(result_iter)
+            for fn in self._lazymap_fns:
+                fn(results)
+            return iter(results)
+        return result_iter
+
+class LazyMapManager(models.Manager):
+
+    def get_query_set(self):
+        return LazyMapQuerySet(self.model)