#django

hello #django. Guys, I'm having some difficulties to understand how can I select all objects in a ManyToMany field that are set on other model. Here is the models.pyhttps://dpaste.de/OwkbQ/

mymode.m2mfield.all()

I think I did not understand select_related() yet

org.instructors.all()

select_related is an optimisation tool

And it doesn't apply to M2Ms anyway.

oh.. gotcha.

in which case can I use select_related ?

when you have a fkey

You would use prefetch_related for your case.

Maybe. It depends on the situation.

you can ask the ORM to fetch the target of that select_related in the same query, instead of waiting for you to access it

RileyII: s/would/could/

FunkyBob: the problem is that I'll have to do a loop for all Org objects and then get the org.instructors.all()

Could, yes.

mmello: well, what is it you actually want?

oh, you want all the Person instances that are related to _any_ Org?

I want to get all Persons in any Org

yes

is there a way to avoid the loop in this case?

Person.objects.filter(org_set__isnull=False) # org_set? or org? ...never seem to remember

hm.. lemme see

not worked :( that is my doubt

don't just say "not worked"

what happened?

what did you use?

we can't help you fix it if you don't tell us _how_ it went wrong

sure thing. lemme show

FunkyBob: it says that org_set is not field

so use org

org__isnull=False

Person.objects.filter(org__isnull=False)

worked

but, I got all Person objects

and not only the objects that are set on m2m field on Org

mmello: So you're trying to load all of the Person instances that have more than zero associated Org instances? Is that it?

mmello: thats what I asked if you wanted

(00:00) < FunkyBob> oh, you want all the Person instances that are related to _any_ Org?

RileyII: I want to get all the Person instances that are also set on Org.instructors as well

you have the set of Person objects which have a relation through that m2m to at least one Org

ahoy

morning, QuanSai

FunkyBob: some Org instances does not contains any instructors yet. but other Org do. So, I could get all those Person objects by doing a loop on Org and putting in a list the Org.instructors.all(). But I was wondering how I can do that with the ORM

So Person.objects.filter(org__in=Org.objects.all()) then? (This solution isn't very efficient, and there may be a better way.)

mmello: I don't understand what's wrong with my solution

RileyII: this works, but it brings me all the Person objects and not only the instructors

you want the list of Persons associated with any Org?

FunkyBob: yes

well, that's what I gave you

I have 91 objects on Person() class ok?

you probably want a distinct() on it too

and just 2 of those Person() are present on Org.instructor

so, I want only that 2 persons be listed

ok

and how many did my suggested query yield?

91

is there any other relation between Person and Org ?

len(Person.objects.filter(org__in=Org.objects.all()))

91

that's not what I recommended

len(Person.objects.filter(org__isnull=False))

91

try exclude(org__isnull=True)

is there any other relation between Person and Org ?

yes.. there is other field

on Org

.. what other field?

on Org

tech = models.ForeignKey(Person)

tech = models.ForeignKey(Person, selected_related='tech')

and neither have a related_name ?

yes.. both has

select_realted? you can't ut that on a fkey

sorry.. I copied wrong.. it's related_name='tech'

and not selected_related

lemme try the exclude

Person.objects.filter(instructors__isnull=False) try that, then try exclude

that related name doesn't make a lot of sense, semantically

I'm translating the names because the code is written in Portguese

with exclude()

ok

same 91

lemme show you in pt_BR the objects

you need to use the related name

I'm having doubts that your data looks the way you think it looks.

len(Filiado.objects.filter(entidade__isnull=False).exclude(entidade__isnull=True))

91

where Filiado = Person

Entidade = Org

lemme pastebin

you only need one of filter or exclude

len(Filiado.objects.exclude(entidade__isnull=True))

don't forget to pastebin the actual models, please

91

yes.. doing now

I wish south had the ability to handle a --edit flag, that would open the newly created migration in your $EDITOR

schinckel: ooh, that'd be nice

here is in pt_BR

Guess it is something I should bug andrew about for the new stuff, though.

mmello: Have you looked at your data to confirm that it looks the way you expect?

RileyII: yes.. I checked

lemme do a for to show you

look

for some reason, my template isn't being accessed. The path is correct. Not sure why Django is reporting that the template doesn't exist. What should I paste to show you guys what I'm doing?

RileyII: makes sense now