I'm having a performance problem where I need to replace section of my query statement. Right now I have a the following:
select count(*) FROM "mytable" WHERE "field" IN ('v1', 'v2', ..., 'vN');
this can be translated to Django ORM:
Mytable.objects.all().filter(field__in=[myvalues]).count()
I need to do the following though:
select count(*) FROM "mytable" JOIN (values ('v1', 'v2', ..., 'vN')) as lookup(value) on lookup.value = "mytable".field;
Is there a way to add this to the ORM? I need to do with ORM because I already have other filters. Worst case scenario I thought of getting the query string and adding there manually...
I'm using Postgresql 9.6
I found a way after reading over and over the documentation. I even found a patch that was not merged a while ago.
It doesn't really do the join, but it works much faster than using __in straightforward.
What I'm doing is executing a RawSQL() that was introduced in Django 2.0 and with that result I do the __in again.
So here is a code example:
query = """select myfield from mytable join (values
('v1'), ('v2'), ..., ('vN')
) as lookup(value) on lookup.value = mytable.myfield"""
r = RawSQL(query, [])
mymodel.filter(myfield__in=r)
Now it takes miliseconds instead of minutes!
Related
I have this query which selects values from two different tables and used array agg over matched IDs how can I get same results using the queryset. Thank you!
select
sf.id_s2_users ,
array_agg(sp.id)
from
s2_followers sf
left join s2_post sp on
sp.id_s2_users = sf.id_s2_users1
where
sp.id_s2_post_status = 1
and sf.id_s2_user_status = 1
group by
sf.id_s2_users
You can run raw SQL queries with Django's ORM if that's what you wanted. You don't have to change your query in that case, you can check documentation here.
Newcommer to Django here.
I'm currently trying to fetch some data from my model with a query that need would need a GROUP BY in SQL.
Here is my simplified model:
class Message(models.Model):
mmsi = models.CharField(max_length=16)
time = models.DateTimeField()
point = models.PointField(geography=True)
I'm basically trying to get the last Message from every distinct mmsi number.
In SQL that would translates like this for example:
select a.* from core_message a
inner join
(select mmsi, max(time) as time from core_message group by mmsi) b
on a.mmsi=b.mmsi and a.time=b.time;
After some tries, I managed to have something working similarly with Django ORM:
>>> mf=Message.objects.values('mmsi').annotate(Max('time'))
>>> Message.objects.filter(mmsi__in=mf.values('mmsi'),time__in=mf.values('time__max'))
That works, but I find my Django solution quite clumsy. Not sure it's the proper way to do it.
Looking at the underlying query this looks like this :
>>> print(Message.objects.filter(mmsi__in=mf.values('mmsi'),time__in=mf.values('time__max')).query)
SELECT "core_message"."id", "core_message"."mmsi", "core_message"."time", "core_message"."point"::bytea FROM "core_message" WHERE ("core_message"."mmsi" IN (SELECT U0."mmsi" FROM "core_message" U0 GROUP BY U0."mmsi") AND "core_message"."time" IN (SELECT MAX(U0."time") AS "time__max" FROM "core_message" U0 GROUP BY U0."mmsi"))
I'd appreciate if you could propose a better solution for this problem.
Thanks !
You only need something like this:
Message.objects.all().distinct('mmsi').values('mmsi', 'time').order_by('mmsi','-id')
or like this:
Message.objects.all().values('mmsi').annotate(date_last=Max('time'))
Note: the last is translate by Django in this sql query:
SELECT "message"."mmsi", MAX("message"."time") AS "date_last" FROM "message" GROUP BY "message"."mmsi", "message"."time" ORDER BY "message"."time" DESC
Using the answers and comments, I managed to solve this using a subquery or a simple distinct order by.
Simple distinct order by solution inspired by #Oriphiel answer:
Message.objects.distinct('mmsi').order_by('mmsi','-time')
The underlying SQL query looks like this :
SELECT DISTINCT ON ("core_message"."mmsi") "core_message"."id", "core_message"."mmsi", "core_message"."time", "core_message"."point"::bytea
FROM "core_message"
ORDER BY "core_message"."mmsi" ASC, "core_message"."time" DESC
Simple and straightforward.
Subquery solution inspired by #DanielRoseman comment:
time_order=Message.objects.filter(mmsi=OuterRef('mmsi')).order_by('-time')
Message.objects.filter(id__in=Subquery(time_order.values('id')[:1]))
The underlying SQL query looks like this :
SELECT "core_message"."id", "core_message"."mmsi", "core_message"."time", "core_message"."point"::bytea
FROM "core_message"
WHERE "core_message"."id" IN
(SELECT U0."id" FROM "core_message" U0 WHERE U0."mmsi" = ("core_message"."mmsi") ORDER BY U0."time" DESC LIMIT 1)
A tad more complex but it gives more flexibility. If I wanted to get first five messages for every MMSI, I'd just need to change the LIMIT value. In Django, it would look like this :
Message.objects.filter(id__in=Subquery(time_order.values('id')[:5]))
I needed to get all the rows in the table1 even if it is not existing in table2 and display it as zero. I got it using raw sql query but in django ORM i am getting the values existing only in table2. The only difference on my django orm is that iI am using inner join while in the raw sql query I am using left join. Is there any way to achieve this or should I use raw sql query? Thanks.
Django ORM:
total=ApplicantInfo.objects.select_related('source_type').values('source_type__source_type').annotate(total_count=Count('source_type'))
OUTPUT OF DJANGO ORM IN RAW SQL:
SELECT "applicant_sourcetype"."source_type", COUNT("applicant_applicantinfo"."source_type_id") AS "total_count" FROM "applicant_applicantinfo" INNER JOIN "applicant_sourcetype" ON ("applicant_applicantinfo"."source_type_id" = "applicant_sourcetype"."id") GROUP BY "applicant_sourcetype"."source_type"
RAW SQL:
SELECT source.source_type, count(info.source_type_id) as total_counts from applicant_sourcetype as source LEFT JOIN applicant_applicantinfo as info ON source.id = info.source_type_id GROUP BY source.id
You cannot query on ApplicantInfo if you want a left join with it. Query on SourceType instead:
qs = (SourceType.objects
.values('source_type')
.annotate(cnt=Count('applicantinfo'))
.values('source_type', 'cnt')
)
Since you haven't posted the models, you may need to adapt the field names to make it work.
class Log:
project = ForeignKey(Project)
msg = CharField(...)
date = DateField(...)
I want to select the four most recent Log entries where each Log entry must have a unique project foreign key. I've tries the solutions on google search but none of them works and the django documentation isn't that very good for lookup..
I tried stuff like:
Log.objects.all().distinct('project')[:4]
Log.objects.values('project').distinct()[:4]
Log.objects.values_list('project').distinct('project')[:4]
But this either return nothing or Log entries of the same project..
Any help would be appreciated!
Queries don't work like that - either in Django's ORM or in the underlying SQL. If you want to get unique IDs, you can only query for the ID. So you'll need to do two queries to get the actual Log entries. Something like:
id_list = Log.objects.order_by('-date').values_list('project_id').distinct()[:4]
entries = Log.objects.filter(id__in=id_list)
Actually, you can get the project_ids in SQL. Assuming that you want the unique project ids for the four projects with the latest log entries, the SQL would look like this:
SELECT project_id, max(log.date) as max_date
FROM logs
GROUP BY project_id
ORDER BY max_date DESC LIMIT 4;
Now, you actually want all of the log information. In PostgreSQL 8.4 and later you can use windowing functions, but that doesn't work on other versions/databases, so I'll do it the more complex way:
SELECT logs.*
FROM logs JOIN (
SELECT project_id, max(log.date) as max_date
FROM logs
GROUP BY project_id
ORDER BY max_date DESC LIMIT 4 ) as latest
ON logs.project_id = latest.project_id
AND logs.date = latest.max_date;
Now, if you have access to windowing functions, it's a bit neater (I think anyway), and certainly faster to execute:
SELECT * FROM (
SELECT logs.field1, logs.field2, logs.field3, logs.date
rank() over ( partition by project_id
order by "date" DESC ) as dateorder
FROM logs ) as logsort
WHERE dateorder = 1
ORDER BY logs.date DESC LIMIT 1;
OK, maybe it's not easier to understand, but take my word for it, it runs worlds faster on a large database.
I'm not entirely sure how that translates to object syntax, though, or even if it does. Also, if you wanted to get other project data, you'd need to join against the projects table.
I know this is an old post, but in Django 2.0, I think you could just use:
Log.objects.values('project').distinct().order_by('project')[:4]
You need two querysets. The good thing is it still results in a single trip to the database (though there is a subquery involved).
latest_ids_per_project = Log.objects.values_list(
'project').annotate(latest=Max('date')).order_by(
'-latest').values_list('project')
log_objects = Log.objects.filter(
id__in=latest_ids_per_project[:4]).order_by('-date')
This looks a bit convoluted, but it actually results in a surprisingly compact query:
SELECT "log"."id",
"log"."project_id",
"log"."msg"
"log"."date"
FROM "log"
WHERE "log"."id" IN
(SELECT U0."id"
FROM "log" U0
GROUP BY U0."project_id"
ORDER BY MAX(U0."date") DESC
LIMIT 4)
ORDER BY "log"."date" DESC
I was following the documentation on FullTextSearch in postgresql. I've created a tsvector column and added the information i needed, and finally i've created an index.
Now, to do the search i have to execute a query like this
SELECT *, ts_rank_cd(textsearchable_index_col, query) AS rank
FROM client, plainto_tsquery('famille age') query
WHERE textsearchable_index_col ## query
ORDER BY rank DESC LIMIT 10;
I want to be able to execute this with Django's ORM so i could get the objects. (A little question here: do i need to add the tsvector column to my model?)
My guess is that i should use extra() to change the "where" and "tables" in the queryset
Maybe if i change the query to this, it would be easier:
SELECT * FROM client
WHERE plainto_tsquery('famille age') ## textsearchable_index_col
ORDER BY ts_rank_cd(textsearchable_index_col, plainto_tsquery(text_search)) DESC LIMIT 10
so id' have to do something like:
Client.objects.???.extra(where=[???])
Thxs for your help :)
Another thing, i'm using Django 1.1
Caveat: I'm writing this on a wobbly train, with a headcold, but this should do the trick:
where_statement = """plainto_tsquery('%s') ## textsearchable_index_col
ORDER BY ts_rank_cd(textsearchable_index_col,
plainto_tsquery(%s))
DESC LIMIT 10"""
qs = Client.objects.extra(where=[where_statement],
params=['famille age', 'famille age'])
If you were on Django 1.2 you could just call:
Client.objects.raw("""
SELECT *, ts_rank_cd(textsearchable_index_col, query) AS rank
FROM client, plainto_tsquery('famille age') query
WHERE textsearchable_index_col ## query
ORDER BY rank DESC LIMIT 10;""")