#django

what about this: http://stackoverflow.com/a/21048821/6062096

but i don't understand clearly how to implement it

iniglo: no problem! sorry I couldn't be more helpful

MikiSoft: that's very clever but I think going down the prefetch route might be easier

yeah this is too complicated for me

how to do a prefetch?

i should first query Like objects and then pull from them Event ones, right?

I haven't done this in years so I wouldn't be the best person to guide you

sorry to repeat simple question how to edit datetime created and updated fields according to create and update with datetime widget ? https://dpaste.de/r4oR

MikiSoft: http://stackoverflow.com/a/28274847/447485

hmm

Event.objects.prefetch_related('like')

this doesn't work

maybe i have to add a field 'likes' in Event?

which is a generic relation to Like model

Event.objects.all().prefetch_related('content_object')

check the UPDATE: part of the answer

You need to do Like.objects.filter(personthing).prefetch_related('events')

ytsejam: If you define your fields with auto_now or auto_now_add django will not let you edit them.

Like.objects.filter(person=User.objects.first()).prefetch_related('events')

returns me of course Like object

pardon me, this: Like.objects.filter(person=User.objects.first()).prefetch_related('content_object')

yes - but you can loop through them and collect the events

if i put 'events' it doesn't work

OK

it's the same as: Like.objects.filter(person=User.objects.first())

cnk : both will be simply models.DateTimeField() that is all . am I right that ?

yes

so what's the difference between the query with `prefetch_related` and without it?

but you will need to fill them in in your forms or they will end up complaining they can't be blank / null

prefetch_related does a second query for all hte related events

oh

so if you loop through the likes to collect the events, they are in memory and don't do n queries to retrieve the events

i get it now

thanks

MikiSoft: the cleanest may be https://docs.djangoproject.com/en/1.10/topics/d...

write the SQL you need and then call Event.objects.raw(SQLHERE)

I recommend reading through prefetch_related() and Prefetch() docs, and enabling logging of database queries so that you can check for performance

you can *probably* do this without raw SQL

but how

by reading the docs

also i don't know so well SQL

you can't do django without knowing SQL

you're going to hit a wall sooner or later

what would be a SQL command for this?

the ORM is an abstraction layer, but it's very important to know what it is doing

you can get the SQL with .query

Like.objects.filter(person_id=1).prefetch_related('content_object').query

airstrike: will that show both queries? or only the one on Like?

i can use something like this: print(Event.objects.filter(business__manager=User.objects.first()).query)

good question

it returns me

SELECT "main_event"."id", "main_event"."business_id", "main_event"."text", "main_event"."when" FROM "main_event" INNER JOIN "main_business" ON ("main_event"."business_id" = "main_business"."id") WHERE "main_business"."manager_id" = 2

cnk: not sure

>>> print(Event.objects.all().prefetch_related('content_object').query)

SELECT "main_event"."id", "main_event"."business_id", "main_event"."text", "main_event"."when" FROM "main_event"

oh wait

>>> print(Like.objects.filter(person=User.objects.first()).prefetch_related('content_object').query)

SELECT "main_like"."id", "main_like"."person_id", "main_like"."content_type_id", "main_like"."object_id", "main_like"."is_dislike" FROM "main_like" WHERE "main_like"."person_id" = 1

i prefer doing it in ORM (django) way

so if i knew how to implement this: http://stackoverflow.com/a/21048821/6062096

i would go by that way

or using prefetch_related

you need to try a few things

go through the frustration of not knowing the answer

i don't know which of that two is better

and then finally figuring it out

otherwise you'll never learn

and your goal should be to learn not the solution, not just solve this one issue

the first solution isn't noob friendly unfortunately

the best solution to any problem is knowing how to properly find the solution

so i can't wrap the head around it

the first solution creates an on-the-fly class through a factory function called subclass_for_content_type()

the first one looks complicated to me

maybe it's not

but after implementing i can use filtering on generic relations

which is good

google 'generic relations prefetch_related' and go through the first 10 hits and any related link

then come back

Quick question: is there a way for AuthenticationForm to raise custom validation error or should i Subclass and override clean()

i understand how to go with prefetch_related way

you're not just going to have a solution fall from the sky

but i don't understand the first one

Try it. You will know more after you have played with it. Just make a branch and drop and recreate your dev database

so if i use this query: Like.objects.filter(person=User.objects.first()).prefetch_related('content_object')

then i have to loop through all of the objects i get and pull from there events?

do you want to get likes or do you want to get events?

events

then it should be Event.objects... something

where certain person gave like

i thought the same and it worked when i still haven't implemented generic relations

Events.objects.filter(like__person=User.objects.first())

it was plain simple

*Event.objects...

and now i'm stuck

since it doesn't work anymore

1. read more about GenericForeignKey and how it works

2. read more about prefetch_related()

3. google both terms together

that's all you need to know from us

MikiSoft: your SQL https://dpaste.de/YL95

and I am done

thank you very much cnk

cnk, i've made a function from your sql query: https://dpaste.de/F8yw

and when i go like this

for obj in generic_filter(1, Event, 'like'):

print(obj)

it throws an exception: django.db.utils.OperationalError: no such column: content_type

This is really not OK as it stands because you are using string interpolation with data that may come from users