[Erp5-dev] getNextNegativeInventoryDate - specification, implementation

[Łukasz Nowak]

Hello,

At Ventis we are playing a lot[1] with warehouse movements - purchase,
production, sale and internal packing lists and inventories.

To generate supply orders (purchase and production) we are using order
builders (modified a little).

And those order builders are using getNextNegativeInventoryDate 
(extended by min_stock property support in our implementation, but
that's not that case).

getNextNegativeInventoryDate works all right almost all the time, but
little problem rises with precision of dates in movement table. Let's
imagine this situation:

 a) 2008/02/15 receive quantity=10.0 of resource
 b) 2008/02/15 send    quantity=5.0  of resource

Of course a) will always happen before b) in reality. But our precision
is one day.

getNextNegativeInventoryDate is querying sorting by date. With our
precision there is possibility, that b) will be returned before a) and
than 2008/02/15 will be day of next negative inventory date. What is of
course wrong.

We were thinking about such solutions:
 1) set more precision on all forms related to reciving/sending goods -
eg. to one minute
 2) relax "precision" on getNextNegativeInventoryDate to given time
amount


Solution 1) should be nice, but there is too detailed in our case - we
are interested only in precision of a day.

So we chosen solution 2) - getNextNegativeInventoryDate is grouping
movements in sets of given precision, sum amount on them and then
starting to walking through such prepared list to give next negative
inventory date. Well - it is working and hadn't destroyed our unit
tests.

So my questions:

 * Did anyone spotted such problem - any tips to share?
 * What shall be Nexedish solution in this case?
 * As this problem appears only in case getNextNegativeInventoryDate is
it "good enough" to patch only this method, and left users with nicer
interface (our warehouse manager would kill me, if I would tell him,
that he would need to type minutes of goods receive/send)?
 * Where I could find more deep technical information about border
issues on stocks (code not counts as "deep technical information" ;) )

Please note that I wanted to left user interface with precision to
one day, but provide some magic, which would insert data with more
precision - maybe time when operation happens - but it would only
introduce many hard to find bugs into system, and more - such data
would be "lies", and we do not want to have lies in our system - from
our point of view, better solution is to have little, but defined,
inaccuracy of data, than to have them theoretically accurate, but
wrong.

Regards,
Luke


[1]..."a lot" - from our point of view ;)
-- 
Łukasz Nowak R&D Ventis http://www.ventis.com.pl/
tel: +48 32 768 16 85 fax: +48 32 392 10 61
``Use the Source, Luke...'' I am only craftsman.