[Answered ]-Django: How to use select_related to INNER JOIN FK's FK

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1👍

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select_related() joins all these three models in one query:

>>> from app.models import Task
>>> task = Task.objects.all().select_related()[0]
>>> task.project.job.job_number
u'123'
>>> from django.db import connection
>>> len(connection.queries)
1
>>> connection.queries
[{u'time': u'0.002', u'sql': u'QUERY = u\'SELECT "app_task"."id", "app_task"."project_id", "app_project"."id", "app_project"."job_id", "app_job"."job_number" FROM "app_task" INNER JOIN "app_project" ON ( "app_task"."project_id" = "app_project"."id" ) INNER JOIN "app_job" ON ( "app_project"."job_id" = "app_job"."job_number" ) LIMIT 1\' - PARAMS = ()'}]
>>>

Readable SQL:

SELECT "app_task"."id", "app_task"."project_id", "app_project"."id",
       "app_project"."job_id", "app_job"."job_number"
FROM "app_task"
INNER JOIN "app_project" ON ( "app_task"."project_id" = "app_project"."id" )
INNER JOIN "app_job" ON ( "app_project"."job_id" = "app_job"."job_number" )
👤catavaran

1👍

You can use a filter:

task = Task.objects.all().select_related().filter(
    project__id__isnull=False, 
    job__id__isnull=False)
👤Iasmini Gomes

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