Acq exchange rates applied at wrong times

[Lebbeous Fogle-Weekley]

To quote Sharon Herbert of Sitka:

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If the exchange rate set in the system is changed it does not affect any currently encumbered
amounts. It does, however, cause the total allocated to change in any funds that have had money
transferred between funds of different currencies. It appears as if the fund is trying to adjust based on the new exchange rate, but it shouldn't as the money has been transferred and is in the new currency
from the moment it is transferred. This does not appear to affect funds that have not had money
transferred into them from a fund of a different currency.

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To restate:
  1) changes to exchange rates do not affect current encumbrances related to the funds made of the affected currency, but they should.
  2) changes to exchange rates should not affect amounts already transferred between finds in different currencies, but they do.

Can I get some confirmation that I'm understanding the issue correctly?

My impression of possible action looks like this, but it will require the participation of other developers with knowledge of Acq:

For 1) we may need a mechanism by which updates to exchange rates trigger changes to encumbrances (rows in acq.fund_debit where encumbrance is true), but this may not be enough.
For 2) we may need to review how fund transfers are handled internally, and consider whether we need the acq.fund_transfer table to get a new column to store the effective exchange rate at the time of transfer, so that we don't look up the exchange rate in the future when it will have changed.

Overall, we need some design work on how changing exchange rates are supposed to work in Evergreen Acq. I'm not aware of a documented design or plan at this time that could comprehensively address how exchange rates need to work in Acq.

[Liam Whalen (whalen-ld)]

I have a fix for this in the following bug.

https://bugs.launchpad.net/evergreen/+bug/1335668