Bypassing cache for function field.

[Jon Levy]

When a function field is accessed multiple times without there being any database operations, it will be calculated the first time, cached, and subsequently recalled out of cache. https://github.com/tryton/trytond/blob/1af9530e187d766598afd55bb6399ab0a5e8689b/trytond/model/modelstorage.py#L1232

The only way to prevent this that I can find (without messing with internals) is to do a database operation (and thus increment the transaction counter), signaling to the numerous caches that they should clear. https://github.com/tryton/trytond/blob/1af9530e187d766598afd55bb6399ab0a5e8689b/trytond/cache.py#L219

Of course, explicitly changing the transaction counter would also accomplish the aim. Does anyone know if this is acceptable?

I understand that I should probably not even be talking about such things. Why would the function field have changed without a database operation? I am in a strange case where I have a function field that is used to generate a report, but new legal guidance has been issued that creates two interpretations of how that function field might be calculated. I have a wizard that runs a series of reports, and the idea is to now have two versions of the report: one for each method of calculating the function field (based on a context flag). I understand that this is not great, and that idiomatically the better thing to do would be to either convert the function field into a regular python method, or use two different function fields. I am just not investing the time to do that yet--in part because I think there is a good possibility of new legal guidance coming out fairly soon.

Any advice on how to not use the cache? (Btw, the avenue of doing a trivial database operation to increment the counter also runs into problems because reports are run in readonly transactions.)

[Cédric Krier]

As you said that your computation depend on the context, you should
instantiate the record with each context. This way the computation will
be redone.

--
Cédric Krier - B2CK SPRL
Email/Jabber: cedric...@b2ck.com
Tel: +32 472 54 46 59
Website: http://www.b2ck.com/

[Jon Levy]

On Thursday, August 2, 2018 at 6:25:06 PM UTC-4, Cédric Krier wrote:
> . . . you should

> instantiate the record with each context. This way the computation will
> be redone.

Perfect. Thanks.