Feature request: make it possible to "tell" filter that would result a
join, to add an additional condition to that join
Consider the following models:
Country:
name # CharField
slug # SlugField
Topic:
name # CharField
slug # SlugField
Project:
name # CharField
slug # SlugField
topic = ForeignKey(Topic)
budget # IntegerField
ProjectLocation
project = ForeignKey(Project)
country = ForeignKey(Country)
latitude # DecimalField
longitude # DecimalField
I want to calculate total amounts per country for projects that are located
in certain countries.
If I do so, finally filtering on Country.slug, I also get totals for
countries that aren't in the selection.
The produced query is similar to the following:
SELECT DISTINCT `website_country`.`name`,
`website_country`.`slug`,
SUM(`website_project`.`budget`) AS `total_budget`
FROM `website_project`
LEFT OUTER JOIN `website_projectlocation`
ON (`website_project`.`id` =
`website_projectlocation`.`project_id`)
LEFT OUTER JOIN `website_country`
ON (`website_projectlocation`.`country_id` =
`website_country`.`id`)
INNER JOIN `website_topic`
ON (`website_project`.`topic_id` = `website_topic`.`id`)
INNER JOIN `website_projectlocation` T7
ON (`website_project`.`id` = T7.`project_id`)
INNER JOIN `website_country` T8
ON (T7.`country_id` = T8.`id`)
WHERE (`website_topict`.`slug` IN ("child-education") AND
T8.`iso2` IN ("MY", "BI", "MW"))
GROUP BY `website_country`.`name`, `website_country`.`slug`
ORDER BY NULL
When I change the query to the following it works as needed:
SELECT DISTINCT `website_country`.`name`,
`website_country`.`slug`,
SUM(`website_project`.`budget`) AS `total_budget`
FROM `website_project`
LEFT OUTER JOIN `website_projectlocation`
ON (`website_project`.`id` =
`website_projectlocation`.`project_id`)
LEFT OUTER JOIN `website_country`
ON (`website_projectlocation`.`country_id` = `website_country`.`id`
AND `website_country`.`iso2` IN ("MY", "BI", "MW"))
INNER JOIN `website_topic`
ON (`website_project`.`topic_id` = `website_topic`.`id`)
INNER JOIN `website_projectlocation` T7
ON (`website_project`.`id` = T7.`project_id`)
INNER JOIN `website_country` T8
ON (T7.`country_id` = T8.`id`)
WHERE (`website_topict`.`slug` IN ("child-education") AND
T8.`iso2` IN ("MY", "BI", "MW"))
GROUP BY `website_country`.`name`, `website_country`.`slug`
ORDER BY NULL
Thus, it would be great to be able to tell somewhere in the filtering that
certain filter should be applied also as additional statement for the
appropriate JOIN.
For example, instead of:
Project.filter(projectlocation__country__slug__in=['MY', 'BI', 'MW'])
the following
Project.filter(projectlocation__country__slug__in=['MY', 'BI', 'MW'],
use_in_joins=True)
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