معرفی شرکت ها
django-batch-select-0.2.4
تبلیغات ما
مشتریان به طور فزاینده ای آنلاین هستند. تبلیغات می تواند به آنها کمک کند تا کسب و کار شما را پیدا کنند.
مشاهده بیشتر
تبلیغات ما
مشتریان به طور فزاینده ای آنلاین هستند. تبلیغات می تواند به آنها کمک کند تا کسب و کار شما را پیدا کنند.
مشاهده بیشتر
تبلیغات ما
مشتریان به طور فزاینده ای آنلاین هستند. تبلیغات می تواند به آنها کمک کند تا کسب و کار شما را پیدا کنند.
مشاهده بیشتر
تبلیغات ما
مشتریان به طور فزاینده ای آنلاین هستند. تبلیغات می تواند به آنها کمک کند تا کسب و کار شما را پیدا کنند.
مشاهده بیشتر
تبلیغات ما
مشتریان به طور فزاینده ای آنلاین هستند. تبلیغات می تواند به آنها کمک کند تا کسب و کار شما را پیدا کنند.
مشاهده بیشترتوضیحات
batch select many-to-many and one-to-many fields (to help avoid n+1 query problem)
| ویژگی | مقدار |
|---|---|
| سیستم عامل | - |
| نام فایل | django-batch-select-0.2.4 |
| نام | django-batch-select |
| نسخه کتابخانه | 0.2.4 |
| نگهدارنده | [] |
| ایمیل نگهدارنده | [] |
| نویسنده | John Montgomery |
| ایمیل نویسنده | john@littlespikeyland.com |
| آدرس صفحه اصلی | http://github.com/lilspikey/django-batch-select/ |
| آدرس اینترنتی | https://pypi.org/project/django-batch-select/ |
| مجوز | BSD |
===================
Django Batch Select
===================
The idea of Django Batch Select is to provide an equivalent to
Django's select_related_ functionality. As of such it's another handy
tool for avoiding the "n+1 query problem".
select_related_ is handy for minimizing the number of queries that need
to be made in certain situations. However it is only usual for
pre-selecting ForeignKey_ relations.
batch_select is handy for pre-selecting ManyToManyField_ relations and
reverse ForeignKey_ relations.
It works by performing a single extra SQL query after a QuerySet_ has
been evaluated to stitch in the the extra fields asked for. This requires
the addition of a custom Manager_, which in turn returns a custom QuerySet_
with extra methods attached.
Example Usage
=============
Assuming we have models defined as the following::
from batch_select.models import BatchManager
class Tag(models.Model):
name = models.CharField(max_length=32)
class Section(models.Model):
name = models.CharField(max_length=32)
objects = BatchManager()
class Entry(models.Model):
title = models.CharField(max_length=255)
section = models.ForeignKey(Section, blank=True, null=True)
tags = models.ManyToManyField(Tag)
objects = BatchManager()
I'll also define a helper function to show the SQL queries generated::
from django import db
def show_queries():
for query in db.connection.queries:
print query["sql"]
db.reset_queries()
Here are a few example (with generated sql queries)::
>>> Entry.objects.batch_select('tags').all()
[]
>>> show_queries() # no results, so no 2nd query
SELECT "batch_select_entry"."id", "batch_select_entry"."title", "batch_select_entry"."section_id" FROM "batch_select_entry"
>>> Entry.objects.create()
>>> Entry.objects.create()
>>> tag1 = Tag.objects.create(name='tag1')
>>> tag2 = Tag.objects.create(name='tag2')
>>> db.reset_queries()
>>> entries = Entry.objects.batch_select('tags').all()
>>> entry = entries[0]
>>> print entry.tags_all
[]
>>> show_queries()
SELECT "batch_select_entry"."id", "batch_select_entry"."title", "batch_select_entry"."section_id" FROM "batch_select_entry" LIMIT 1
SELECT (`batch_select_entry_tags`.`entry_id`) AS "entry_id", "batch_select_tag"."id", "batch_select_tag"."name" FROM "batch_select_tag" INNER JOIN "batch_select_entry_tags" ON ("batch_select_tag"."id" = "batch_select_entry_tags"."tag_id") WHERE "batch_select_entry_tags".entry_id IN (1)
>>> entry.tags.add(tag1)
>>> db.reset_queries()
>>> entries = Entry.objects.batch_select('tags').all()
>>> entry = entries[0]
>>> print entry.tags_all
[<Tag: Tag object>]
>>> show_queries()
SELECT "batch_select_entry"."id", "batch_select_entry"."title", "batch_select_entry"."section_id" FROM "batch_select_entry" LIMIT 1
SELECT (`batch_select_entry_tags`.`entry_id`) AS "entry_id", "batch_select_tag"."id", "batch_select_tag"."name" FROM "batch_select_tag" INNER JOIN "batch_select_entry_tags" ON ("batch_select_tag"."id" = "batch_select_entry_tags"."tag_id") WHERE "batch_select_entry_tags".entry_id IN (1)
>>> entries = Entry.objects.batch_select('tags').all()
>>> for entry in entries:
.... print entry.tags_all
....
[<Tag: Tag object>]
[]
>>> show_queries()
SELECT "batch_select_entry"."id", "batch_select_entry"."title", "batch_select_entry"."section_id" FROM "batch_select_entry"
SELECT (`batch_select_entry_tags`.`entry_id`) AS "entry_id", "batch_select_tag"."id", "batch_select_tag"."name" FROM "batch_select_tag" INNER JOIN "batch_select_entry_tags" ON ("batch_select_tag"."id" = "batch_select_entry_tags"."tag_id") WHERE "batch_select_entry_tags".entry_id IN (1, 2)
Re-running that same last for loop without using batch_select
generate three queries instead of two (n+1 queries)::
>>> entries = Entry.objects.all()
>>> for entry in entries:
.... print entry.tags.all()
....
[<Tag: Tag object>]
[]
>>> show_queries()
SELECT "batch_select_entry"."id", "batch_select_entry"."title", "batch_select_entry"."section_id" FROM "batch_select_entry"
SELECT "batch_select_tag"."id", "batch_select_tag"."name" FROM "batch_select_tag" INNER JOIN "batch_select_entry_tags" ON ("batch_select_tag"."id" = "batch_select_entry_tags"."tag_id") WHERE "batch_select_entry_tags"."entry_id" = 1
SELECT "batch_select_tag"."id", "batch_select_tag"."name" FROM "batch_select_tag" INNER JOIN "batch_select_entry_tags" ON ("batch_select_tag"."id" = "batch_select_entry_tags"."tag_id") WHERE "batch_select_entry_tags"."entry_id" = 2
This also works with reverse foreign keys. So for example we can get
this entries that belong to each section::
>>> section1 = Section.objects.create(name='section1')
>>> section2 = Section.objects.create(name='section2')
>>> Entry.objects.create(section=section1)
>>> Entry.objects.create(section=section1)
>>> Entry.objects.create(section=section2)
>>> db.reset_queries()
>>> Section.objects.batch_select('entry_set')
[<Section: Section object>, <Section: Section object>]
>>> show_queries()
SELECT "batch_select_section"."id", "batch_select_section"."name" FROM "batch_select_section" LIMIT 21
SELECT ("batch_select_entry"."section_id") AS "__section_id", "batch_select_entry"."id", "batch_select_entry"."title", "batch_select_entry"."section_id", "batch_select_entry"."location_id" FROM "batch_select_entry" WHERE "batch_select_entry"."section_id" IN (1, 2)
Each section object in that query will have an entry_set_all field
containing the relevant entries.
You need to pass batch_select the "related name" of the foreign key,
in this case "entry_set". NB by default the related name for a foreign
key does not actually include the _set suffix, so you can use just "entry"
in this case. I have made sure that the _set suffix version also works to
try and keep the API simpler.
More Advanced Usage
=========================
By default the batch fields are inserted into fields named ``<name>_all``,
on each object. So::
Entry.objects.batch_select('tags').all()
results in the Entry instances having fields called ``'tags_all'``
containing the Tag objects associated with that Entry.
If you want to give the field a different name just use a keyword
argument - in the same way as using the Aggregation_ API::
Entry.objects.batch_select(selected_tags='tags').all()
Would means the Tag objects would be assigned to fields called
``'selected_tags'``.
If you want to perform filtering of the related objects you will need to
use a Batch object. By doing this you can pass extra keyword arguments
in the same way as when using the filter method of a QuerySet::
from batch_select.models import Batch
Entry.objects.batch_select(tags_containing_blue=Batch('tags', name__contains='blue'))
Would return Entry objects with fields called 'tags_containing_name' with
only those Tags whose name contains 'blue'.
In addition to filtering using keyword arguments, you can also call the
following methods on a Batch object, with their effects being passed on
to the underlying QuerySet_ object:
* filter_
* exclude_
* annotate_
* order_by_
* reverse_
* select_related_
* extra_
* defer_
* only_
* batch_select
(Note that distinct(), values() etc are not included as they would have
side-effects on how the extra query is associated with the original query)
So for example to achieve the same effect as the filter above you could
do the following::
from batch_select.models import Batch
Entry.objects.batch_select(tags_containing_blue=Batch('tags').filter(name__contains='blue'))
Whereas the following would exclude tags containing "blue" and order by name::
from batch_select.models import Batch
batch = Batch('tags').exclude(name__contains='blue').order_by('name')
Entry.objects.batch_select(tags_not_containing_blue=batch)
Compatibility
=============
Django batch select should work with Django 1.1-1.3 at least.
TODOs and BUGS
==============
See: http://github.com/lilspikey/django-batch-select/issues
.. _select_related: http://docs.djangoproject.com/en/dev/ref/models/querysets/#id4
.. _ForeignKey: http://docs.djangoproject.com/en/dev/ref/models/fields/#foreignkey
.. _ManyToManyField: http://docs.djangoproject.com/en/dev/ref/models/fields/#manytomanyfield
.. _QuerySet: http://docs.djangoproject.com/en/dev/ref/models/querysets/
.. _Manager: http://docs.djangoproject.com/en/dev/topics/db/managers/
.. _Aggregation: http://docs.djangoproject.com/en/dev/topics/db/aggregation/
.. _filter: http://docs.djangoproject.com/en/dev/ref/models/querysets/#filter-kwargs
.. _exclude: http://docs.djangoproject.com/en/dev/ref/models/querysets/#exclude-kwargs
.. _annotate: http://docs.djangoproject.com/en/dev/ref/models/querysets/#annotate-args-kwargs
.. _order_by: http://docs.djangoproject.com/en/dev/ref/models/querysets/#order-by-fields
.. _reverse: http://docs.djangoproject.com/en/dev/ref/models/querysets/#reverse
.. _extra: http://docs.djangoproject.com/en/dev/ref/models/querysets/#extra-select-none-where-none-params-none-tables-none-order-by-none-select-params-none
.. _defer: http://docs.djangoproject.com/en/dev/ref/models/querysets/#defer-fields
.. _only: http://docs.djangoproject.com/en/dev/ref/models/querysets/#only-fields
نحوه نصب
نصب پکیج whl django-batch-select-0.2.4:
pip install django-batch-select-0.2.4.whl
نصب پکیج tar.gz django-batch-select-0.2.4:
pip install django-batch-select-0.2.4.tar.gz