Re: Update _id field before .save() for ForeignKey

Hi Dvenun,

Bc of  Django implement accord to python, of cause child inherit from parent existence.

https://docs.python.org/3.7/library/functions.html#id

On Sat, Nov 30, 2019, 13:30 Dvenum <dvenum.at@gmail.com> wrote:

Interest idea and it works, but not necessary:
    company = Company()
    #company.id is None

    companies.append(company)
    Company.objects.bulk_create(companies)
    #company.id is 1

Instead to ask pk from database, it can be used from company_value.company.id. Django save pk value to internal meta (models/base.py) and does not update it. This works too:
value.company = value.company     # pk updated

I want to ask, each child object should be created only when parent is saved to db? Maybe django has something to cover this case?

On Sat, Nov 30, 2019 at 7:52 AM Charles Lee <CharlesLee522@gmail.com> wrote:

I have an idea.

1. `bulk_create` all companies.
2. `Filter`(SELECT) all `Company` and make it dictionary for retrieving company fast.
3. 1. company_dict = {
        'Name': 'pk',
        ...
      }
4. Create a list of `CompanyValue` with company name and company_dict.
5. `bulk_create` the list.

I'm not sure if it will work because I haven't implemented it, but I hope it helps. 

2019년 11월 29일 금요일 오후 9시 42분 0초 UTC+9, Maxim Bulatov 님의 말:

Hello,

I have lot of lists like follow:
(Name1): (V1, V2, V3, V4, ..)

And I use many threads to create many db objects:
company = Company(Name)
for x in vector:
    v = CompanyValue(company=company, value=x)
    values.append(v)

class CompanyValue(models.Model):
    company = models.ForeignKey('Company', on_delete=models.CASCADE)
    value = FloatField

This pool of threads return all lists, what I combine, filter and want put to database in one bulk_create call.
Suddenly, I found, company.id is not ready to be linked in CompanyValue, follow code does not works:
Company.objects.bulk_create(companies)
CompanyValue.objects.bulk_create(values)      # value.company_id is null here

No way to save objects in my threads, because I need to filter objects and can do it only when all of them are collected. Also, it has performance issues 100k+ of requests is slowly enough. I have two ways to resolve:
1. I can make intermediate class or tuple and create CompanyValue objects only when companies is saved to db. Hard to support, hard to filter, not so clean.
2. I can use dirty hack to update _id field:
    for v in values:
        v.company = v.company

Can you advice more ways for me? It seems, I don't know something from django features to make it elegant.
I see 11 years old issue here (https://code.djangoproject.com/ticket/9553) and it marked as intended behaviour.

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dvenum

dvenum.at@gmail.com

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