[PonyORM-list] get PK of the record before committing it to DB

Вадим Бажов vadim at ideco.ru
Wed Mar 25 08:28:53 UTC 2015

Hello happy pony users and devs !

I do an import from old db to a new one, driven by pony orm. Import 
iterates over records of customers and their related licences, fetched 
from an old DB. So we have to fill two tables in new DB: Customers table 
and Licence table with records, which have one2many relations (one 
Customer can have many Licences, by PK). PK is an autoincrementing 
integer in both tables.

Within *each iteration* of import i need to write one Customer record 
and its Licences records to new DB. Licence records should have 
customer_id fields filled up with corresponding Customer PKs. Here we 
have a problem:

If we create an object of an entity Customers : cust = 
Customers(name='GazMyas',city='Chelyabinsk') , it wont be recorded to a 
DB exactly at this moment and we wont able to use its ID (pk of the 
record) to bind Licence records to it. In other words there is no 
'cust.id' element at this moment.

We can do a 'commit()' each time we create a Customer object. After that 
'cust.id' comes ready. But in case of monstrous imports with over 20 000 
records committing every record to hdd slows down the import process to 
hours. And hangs up your server hard drive. Anyway, it's a bad practice 
to commit every record walking the huge array of incoming data.

So, by now, I fill up two dicts with Customers records, incrementing 
their ID's manually (customer_id += 1) and Licences records bound to 
this pre-calculated ID's. When dicts are ready, I write them to a new DB 
walking through them.

Is there a better way to complete a data import without filling up 
transition dicts and calculating autoincrement IDs by hand ? Can I 
somehow use PKs of the records before committing them to DB ?
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