Re: Optimal query for related names in onetomany or manytomany using Django Queryset

Hi Vijay,

Thanks for your response.

In my scenario, there is also another model with manytomany relation with A:

class C(models.Model):

    a = manytomany('A', related_name='cs', through='D')

so, for around 25K records in A, 45K records in D and 18K records in B, following query takes more than 300ms and sometimes more than 500ms:

A.objects.filter(bs__isnull=False, cs__isnull=False).

Thanks.

On Saturday, February 3, 2018 at 12:28:38 AM UTC+5:30, Vijay Khemlani wrote:

"with large of records in A and B, the above takes lot of time"

How long? At first glance it doesn't look like a complex query or something particularly inefficient for a DB.

On Fri, Feb 2, 2018 at 11:31 AM, Andy <kaku...@gmail.com> wrote:

not that i know of

Am Freitag, 2. Februar 2018 15:28:26 UTC+1 schrieb Web Architect:

Hi Andy,

Thanks for your response. I was pondering on option a before posting this query thinking there could be better ways in django/SQL to handle this. But now I would probably go with a.

Thanks.

On Friday, February 2, 2018 at 7:50:53 PM UTC+5:30, Andy wrote:

a) Maybe its an option to put the foreign key to the other model? This way you dont need to make a join to find out if there is a relation.

b) Save the existing ralation status to model A

c) cache the A.objects.filter(bs__isnull=False) query

But apart from that i fear you cannot do much more, since this is just a DB and not a Django ORM question.

Am Freitag, 2. Februar 2018 14:47:45 UTC+1 schrieb Web Architect:

Hi,

I am trying to optimise Django queries on my ecommerce website. One of the fundamental query is where I have no clue how to make efficient. It could be trivial and probably been known long time back. But I am new to Django and would appreciate any help. This is primarily for one to many or many to many relations.

Following is an example scenario:

(Please pardon my syntax as I want to put across the concept and not the exact django code unless it's really needed):

Model A:

class A(models.Model):

    # Fields of model A

Model B (which is related to A with foreign key):

class B(models.Model):

    a = models.ForeignKey('A', related_name='bs')

Now I would like to find out all As for which there is atleast one b. The only way I know is as follows:

A.objects.filter(bs__isnull=False)

But the above isn't an optimal way as with large of records in A and B, the above takes lot of time. It gets more inefficient if it's a many to many relationship.

Could anyone please let me know the most efficient way to use django queryset for the above scenario?

Thanks.

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