#23440: select_related with multiple ForeignKey to same table generates
sub-optimal
SQL
-------------------------------------+-------------------------------------
Reporter: djbug | Owner: nobody
Type: | Status: closed
Cleanup/optimization | Version: 1.6
Component: Uncategorized | Resolution: invalid
Severity: Normal | Triage Stage:
Keywords: select_related | Unreviewed
Has patch: 0 | Needs documentation: 0
Needs tests: 0 | Patch needs improvement: 0
Easy pickings: 0 | UI/UX: 0
-------------------------------------+-------------------------------------
Changes (by akaariai):
* status: new => closed
* resolution: => invalid
Comment:
I don't think that actually works. Assume the following on node table:
||id || name
||1 || node 1
||2 || node 2
And relation has one model with left_id = 1 and right_id = 2. Now, the
second query produces results
||id || left_id|| right_id|| node.id || name
||1 || 1 || 2 || 1 ||node 1
||1 || 1 || 2 || 2 ||node 2
Which is not the wanted result. Instead we want all the related objects in
a single row. Trying to collapse the two rows into a single object while
iterating leads to all sorts of really complex issues which we are not
going to tackle.
--
Ticket URL: <https://code.djangoproject.com/ticket/23440#comment:2>
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