Description:
djangoexpressionfilter 0.0.1
About
(WIP)
This package provides a class that enables direct filtering on an expression that you’d usually use as an annotation.
Usage
The class AnnotationBypass takes 3 arguments. The first is any valid annotation value, the second is the lookup string you’d use in the filter kwarg name, the third is the value you’d use for the filter.
from expression_filter import AnnotationBypass
filter = AnnotationBypass(Sum('book__page_count'), 'gte', 1000)
But why
Consider the following:
Book.objects.annotate(words_per_page=F('word_count') / F('page_count')).filter(words_per_page__gte=100)
This executes the following query:
SELECT `books_book`.`id`,
`books_book`.`word_count`,
`books_book`.`page_count`,
`books_book`.`word_count` / `books_book`.`page_count` AS `words_per_page`
FROM `books_book`
WHERE `books_book`.`word_count` / `books_book`.`page_count` >= 100
Notice that the expression is duplicated, as using the words_per_page annotation by name in the WHERE clause is not allowed. Usually the annotated value is not needed in the response, and depending on how complex the annotation is or how many objects are returned, this could have a performance impact.
This is better:
from expression_filter import AnnotationBypass
Book.objects.filter(AnnotationBypass(F('word_count') / F('page_count'), 'gte', 100))
SELECT `books_book`.`id`,
`books_book`.`word_count`,
`books_book`.`page_count`
FROM `books_book`
WHERE `books_book`.`word_count` / `books_book`.`page_count` >= 100
License
For personal and professional use. You cannot resell or redistribute these repositories in their original state.
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