[14.0] Purchase - Picking Count field or picking_count calculation very inefficient

[aliomattux]

Impacted versions:
14.0
Steps to reproduce:
Delete the column purchase_order.picking_count in a database with 20k plus purchase orders
Current behavior:
New field is created and compute is called on each PO. The method iterates over each line item in a PO, selects all of the moves, then groups them by picking id
Expected behavior:
Suggestion: Wouldn't it be immensely easier/more efficient to just have a column purchase_id on stock.picking? Looping through all po lines and associated move lines is a very bad solution to calculate a parent field value.
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Support ticket number submitted via odoo.com/help (optional):

[ryv-odoo]

Hello @aliomattux , Thank you for your report.
I have some remark/question about this:

New field is created and compute is called on each PO

Why the creation of a new field should trigger the compute_picking ? I don't get it.

The method iterates over each line item in a PO, selects all of the moves, then groups them by picking id

At first glance, it shouldn't be a issue with the prefetch and because the store compute should compute a lot (and not on all your DB.

Also, do you have py-flame about this compute, it can greatly help ?