id	summary	reporter	owner	description	type	status	component	version	severity	resolution	keywords	cc	stage	has_patch	needs_docs	needs_tests	needs_better_patch	easy	ui_ux
7110	select_related returns incorrect results when one model has two ForeignKeys to the same model	ElliottM	Jacob	"This started occurring just after the qs-rf branch was merged into trunk.

Essentially, my Connection models has two separate FKs to the Port model (called start and end), the Port model has a FK to the device model, and the Device model has a FK to the building model.

When I want to get a list of all connections that start and end in the same building, I do the following: 

{{{
Connection.objects.filter(start__device__building=building_name, end__device__building=building_name)
}}}


This works correctly for the most part. However, if I add .select_related() onto the end of the line, it all goes wrong. The following is the output from runtest.py in the attachment, which should show the problem:


{{{
>>> from test import runtest
Begin list of normal filter
10      FROM    router/4        TO      switch/7
11      FROM    switch/7        TO      server/1
(end list)



Begin list of filter using select_related
10      FROM    switch/4        TO      switch/7
11      FROM    server/7        TO      server/1
(end list)
}}}

As you can see, in the first list, the start of the first connection is device ""router"", port 4 and the end is device ""switch"", port 7. When the exact same query is done with select_related on the end, the port numbers are the same, but the start device has for some reason been changed to be equal to the end device. From what I read in the documentation, select_related should not affect the output at all, so I believe this must be a bug.

Attached is my whole test app where you can see for yourself what is happening."		closed	Uncategorized	dev		fixed	qsrf-cleanup select_related foreign key		Accepted	0	0	0	0	0	0