The method `read()` may be very slow when reading relational fields and
computed fields, because the computed fields can be computed on a recordset
that is larger than expected.
The issue occurs on model 'res.partner' when reading fields 'child_ids' and
'purchase_order_count', for instance. Suppose we read those two fields on a
partner with 1000 contacts. First, the one2many field is read from the
database and stored to the cache; the latter adds the value ids to the
prefetching of 'res.partner'. Then, the fields are fetched from the cache.
When 'purchase_order_count' is accessed on the partner, the field is computed
on all its children as well...
closesodoo/odoo#29867
Now that we're closer to switching to P3 for good, these helpers have
outlived their usefulness, and mostly add noise.
All remaining dict.iter*() or dict.view*() must be converted to the
normal keys(), values() or items() calls.
Whenever the result is likely to be used for more than the scope of a
loop, or when the dict needs to be modified during iteration, the calls
must be wrapped in a ``list()``, to protect the new P3 semantics.
Those cases are very exceptional.
Also removed some dead code or improved the API to remove unnecessary
conversions.
In Python 3:
* various builtins and dict methods were changed to return
view/iterable objects rather than lists
* and the separate Python 2 view/iterable builtins and methods were
removed altogether
This is problematic when using these items as list (which the happens
repeatedly in Odoo), but more viciously when iterating *multiple times*
over them (which also happens, which I've messed up multiple times while
writing this, and which is a pain to debug even when you've just created
the issue).
Convert all code using these to semantics-matching cross-version
helper functions to get the LCD behaviour between P2 and P3, and
forbid the builtins via lint.
issue #8530
Christophe Simonis