SQL & merge [was Re: Welcome back]

[Linas Vepstas]

An earlier thread voiced concerns about undo for SQL backends.
If an SQL db can support transactions, then there already is a 
natural undo mechanism.   Postgress supports this, I don't think
mysql does.  

Thus, it could work, in principle, as follows:

;; on gnucash startup, issue the SQL BEGIN statement;
;; user does gui stuff, such as hand-entering, or lots of merge, etc.
;; user clicks on "save" menu entry, which causes the SQL COMMIT to be
      issued.
;; user fails to click on save, and instead chooses 'exit w/o save'
      in which case we do an SQL ROLLBACK, and all changes up to
      the previous BEGIN are dumped by the SQL db.

Thus it gets file-system like semantics.  Unfiortuantely, I don't think
one can nest begins/commits :(

Anyway, I'll keep this in mind during the SQL backend work.

--linas

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