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["Olivier Dony \(OpenERP\)" <821583@xxxxxxxxxxxxxxxxxx>]

Hi Sebastien,

First of all, I'd like to point out that this is really only a
performance optimization, but should not affect the correctness of the
results. It seems you describe a situation where you rely on the stored
value because the computation of the function field would not provide a
correct result - this is inconsistent and unsupported. The fnct_inv
function must be the reverse of the fnct function if it is provided,
otherwise you're allowing it to somehow "corrupt" the data. Even if that
suits your business needs, that does not seem like a good practice, and
the system should not guarantee that it will work.

As for the issue of re-computing stored many2one function fields all the time, this is a limitation of the current OpenERP framework, and would happen for any function fields that can be stored but do require a form of postprocessing (_classic_read=False). The only field type with these properties is currently many2one.
What happens it the following: the store parameter is not ignored, but is only used for the initial fetch from the database. Then because the field requires post-processing the value is passed to the get() method of the field.
For a regular many2one field, get() will turn the raw ID values coming from the database into "name_get" pair (ID, Label).
However for function fields there is a conflict: the get() method directly delegates to the `fnct` function implementing the function field, and its signature does not include possible prefetched values, so the prefetched values are ignored.

I see two options:

1. We modify the signature of function fields to include an optional 'stored_values' parameter that may contain the currently stored value for the field, if the field is stored.  That is an API change and short of doing dirty tricks to introspect the functions before calling them, we'd have to update all function fields. We could of course do another dirty hack and pass the 'stored_values' in the context, but in order to benefit from it we'd still need to change the implementation of function fields to properly use it.
So that's only a long-term option.

2. Or we could add some logic to the current get() method of
fields.function to check the contents of the prefetched 'values' before
calling the function implementation, and only call it for the missing
values. We won't be able to distinguish NULL values from values that
have never been computed/stored yet, so we'll have to compute them
anyway, but we'll still get the benefit of not computing the non-NULL
values. This requires no change of API, but will not give function
fields any control on how stored values are used. This is a short-term
option.

I think option 2 is reasonable, and pretty much consistent with the
current API convention: function fields are not supposed to know
anything about their possible storage, only how to compute the result.

What do you think?

** Changed in: openobject-server
       Status: Triaged => Confirmed

** Changed in: openobject-server
     Assignee: OpenERP Publisher's Warranty Team (openerp-opw) => OpenERP's Framework R&D (openerp-dev-framework)

** Summary changed:

- function field type many2one and store=True doesn't work
+ many2one function fields are recomputed every time even with store=True

** Tags added: performance

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https://bugs.launchpad.net/bugs/821583

Title:
  many2one function fields are recomputed every time even with
  store=True

Status in OpenERP Server:
  Confirmed

Bug description:
  Hi
  I am migrating my customer from v5 to v6
  I make some imporvement for is V6 and I have a problem with the function field

  I try to create a function fields with the type many2one and the
  option store=True. The problem is that the field is still read from
  the function and never from the database. It look like the option
  store=True is never use in reading.

  exemple add this field to sale_shop

      def _get_test_id(self, cr, uid, ids, name, args, context=None):
          print 'get test'
          res={}
          for id in ids:
              res[id] = 1
          return res

          'test': fields.function(_get_test_id, type='many2one',
                  relation='product.product', string='Product', method=True,
                  store=True),

  And open the sale shop. You will see that each time the sale_shop is
  open the field test is read from the function "_get_test_id" and not
  directly from the database.

  I have this bug with the last version of openerp 6.0

  I also send a mail to the support team.
  Best Regard

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