This is more a question of understanding how things work than a issue
I'm working with Django 1.9 and Oracle 12 and python 3.4
I have a model Resources
When I do the following query to find all the uid's from matching resources
in the Django shell
* Resources.objects.filter(remote_source=source.pk).values_list('uid')*
I get the following SQL:
DEBUG (0.002) QUERY = 'SELECT * FROM (SELECT "_SUB".*, ROWNUM AS "_RN" FROM
(SELECT "DATA_MASTER"."RESOURCES"."UID" AS Col1 FROM
"DATA_MASTER"."RESOURCES" WHERE
"DATA_MASTER"."RESOURCES"."REMOTE_SOURCE_ID" = :arg0) "_SUB" WHERE ROWNUM
<= 21) WHERE "_RN" > 0' - PARAMS = ('6�mbe�$��S]�\x03\n\x0f�',);
args=(b'6\xcbmbe\xac$\xe7\xe0S]\x99\x03\n\x0f\xce',)
A list of tuples is returned as expected.
However, when I do the same query, but now in a list comprehension to parse
out the uid field I get a different (more optimized) query.
[ x[0] for x in
*Resources.objects.filter(remote_source=a.pk).values_list('uid')* if x[0] ]
DEBUG (0.100) QUERY = 'SELECT "DATA_MASTER"."RESOURCES"."UID" FROM
"DATA_MASTER"."RESOURCES" WHERE
"DATA_MASTER"."RESOURCES"."REMOTE_SOURCE_ID" = :arg0' - PARAMS =
('6�mbe�$��S]�\x03\n\x0f�',);
args=(b'6\xcbmbe\xac$\xe7\xe0S]\x99\x03\n\x0f\xce',)
my question is : why do I get a SELECT * FROM in the first situation and
why a SELECT "DATA_MASTER"."RESOURCES"."UID"
in the second situation. I would expect the SELECT <field> query always in
a values_list query. i.e. how does the django orm know it lives inside the
list comprehension.?
BTW, on PostgreSQL I always get the SELECT <field> query, regardless of the
context.
Cheers Div
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