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 20955,Deep select_related to same model returns incorrect relationship,Alex Hayes,nobody,"When using select_related on a deeply nested relationship and you have two (or possibly more) relationships that use the same model the SQL query is incorrect and thus the resulting model incorrect. This is best illustrated with an example: {{{#!python expect = Task.objects.get(pk=1) actual = Task.objects.select_related('creator__staffuser__staff', 'owner__staffuser__staff').get(pk=1) if actual.creator.staffuser.staff != expect.creator.staffuser.staff: print ""Creator Incorrect"" if actual.owner.staffuser.staff != expect.owner.staffuser.staff: print ""Owner Incorrect"" }}} Outputs ```Owner Incorrect``` == Test Project I've created a test project at https://github.com/alexhayes/deepselectrelated This test project has two tests that illustrates the difference in behaviour. == Issue Location It appears that this issue exists in the actual SQL statements that are being generated, as taken from my test project: {{{#!sql SELECT ""deepselectrelated_task"".""id"", ""deepselectrelated_task"".""title"", ""deepselectrelated_task"".""creator_id"", ""deepselectrelated_task"".""owner_id"", ""auth_user"".""id"", ""auth_user"".""password"", ""auth_user"".""last_login"", ""auth_user"".""is_superuser"", ""auth_user"".""username"", ""auth_user"".""first_name"", ""auth_user"".""last_name"", ""auth_user"".""email"", ""auth_user"".""is_staff"", ""auth_user"".""is_active"", ""auth_user"".""date_joined"", ""deepselectrelated_staffuser"".""user_ptr_id"", ""deepselectrelated_staffuser"".""staff_id"", ""deepselectrelated_staff"".""id"", ""deepselectrelated_staff"".""name"", T5.""id"", T5.""password"", T5.""last_login"", T5.""is_superuser"", T5.""username"", T5.""first_name"", T5.""last_name"", T5.""email"", T5.""is_staff"", T5.""is_active"", T5.""date_joined"", T6.""user_ptr_id"", T6.""staff_id"", ""deepselectrelated_staff"".""id"", ""deepselectrelated_staff"".""name"" FROM ""deepselectrelated_task"" INNER JOIN ""auth_user"" ON ( ""deepselectrelated_task"".""creator_id"" = ""auth_user"".""id"" ) LEFT OUTER JOIN ""deepselectrelated_staffuser"" ON ( ""auth_user"".""id"" = ""deepselectrelated_staffuser"".""user_ptr_id"" ) LEFT OUTER JOIN ""deepselectrelated_staff"" ON ( ""deepselectrelated_staffuser"".""staff_id"" = ""deepselectrelated_staff"".""id"" ) INNER JOIN ""auth_user"" T5 ON ( ""deepselectrelated_task"".""owner_id"" = T5.""id"" ) LEFT OUTER JOIN ""deepselectrelated_staffuser"" T6 ON ( T5.""id"" = T6.""user_ptr_id"" ) }}} Note that there is only one join to the staff table and the following part of the SELECT query is incorrectly repeated: {{{#!sql ""deepselectrelated_staff"".""id"", ""deepselectrelated_staff"".""name"" }}} There should infact be two joins to the staff table and the SELECT should be as follows: {{{#!sql SELECT ""deepselectrelated_task"".""id"", ""deepselectrelated_task"".""title"", ""deepselectrelated_task"".""creator_id"", ""deepselectrelated_task"".""owner_id"", ""auth_user"".""id"", ""auth_user"".""password"", ""auth_user"".""last_login"", ""auth_user"".""is_superuser"", ""auth_user"".""username"", ""auth_user"".""first_name"", ""auth_user"".""last_name"", ""auth_user"".""email"", ""auth_user"".""is_staff"", ""auth_user"".""is_active"", ""auth_user"".""date_joined"", ""deepselectrelated_staffuser"".""user_ptr_id"", ""deepselectrelated_staffuser"".""staff_id"", ""deepselectrelated_staff"".""id"", ""deepselectrelated_staff"".""name"", T5.""id"", T5.""password"", T5.""last_login"", T5.""is_superuser"", T5.""username"", T5.""first_name"", T5.""last_name"", T5.""email"", T5.""is_staff"", T5.""is_active"", T5.""date_joined"", T6.""user_ptr_id"", T6.""staff_id"", T7.""id"", T7.""name"" FROM ""deepselectrelated_task"" INNER JOIN ""auth_user"" ON ( ""deepselectrelated_task"".""creator_id"" = ""auth_user"".""id"" ) LEFT OUTER JOIN ""deepselectrelated_staffuser"" ON ( ""auth_user"".""id"" = ""deepselectrelated_staffuser"".""user_ptr_id"" ) LEFT OUTER JOIN ""deepselectrelated_staff"" ON ( ""deepselectrelated_staffuser"".""staff_id"" = ""deepselectrelated_staff"".""id"" ) INNER JOIN ""auth_user"" T5 ON ( ""deepselectrelated_task"".""owner_id"" = T5.""id"" ) LEFT OUTER JOIN ""deepselectrelated_staffuser"" T6 ON ( T5.""id"" = T6.""user_ptr_id"" ) LEFT OUTER JOIN ""deepselectrelated_staff"" T7 ON ( T6.""staff_id"" = T7.""id"" ) }}}",Bug,closed,"Database layer (models, ORM)",dev,Release blocker,fixed,,,Accepted,0,0,0,0,0,0