[Kmymoney-devel] MyMoneyStorageSql concept

[Fernando Vilas]

On Sunday, January 26, 2014 16:20:54 Christian Dávid wrote:
> Hi,
> 
> is there a description of MyMoneyStorageSql? For me it is hard to understand
> (want to add a new MyMoneyObject to be stored).
> 

Not that I know of...  other than to say that it was designed as a replacement 
for the XML backend. That means that it implements the same functions, though 
maybe not as efficiently as a backend designed around a database from the 
beginning.

If you want to add a new MyMoneyObject to the storage system, it has to work 
in both types of backends. To get there, I would recommend adding it to the 
XML backend first, then translating it over. You could do it the other way, but 
I think it may be harder.

> Am I correct if i say, MyMoneyStorageSql uses only very basic and simple
> sql? E.g. the kmmFileInfo table stores the row count of other tables –
> isn't that a fundamental task of a database to manage that for me? I would
> like to put some more logic in the database, would you like that (e.g.
> using joins)?
> 

It uses very simple SQL to get things done. Issuing a "select count(1) from 
..." seems trivial until you do it a lot and create multiple round-trips to 
the DB to grab the count of each table. It really comes into play with 
importing statements when grabbing the next transactionID can be many round-
trips.

What sort of logic did you have in mind to put into the database? The right 
set of queries to speed things up could be useful.

> Also there is a high abstraction level to create sql Queries, isn't sql an
> abstraction level itself? It would be a lot easier if I can just enter the
> sql statement to execute (within QSqlQuery of course).
> 

There is an additional abstraction layer on top of just writing SQL. It seems 
that even though there is a standard, SQL isn't always SQL. In order to 
support PostgreSQL, MySQL, and SQLite3 (with provisions for others), an 
additional abstraction layer had to be built for the DDL. Once that was built, 
it was easy to go to a system where we can bind variables based on 
standardized (within KMM) select/insert/update strings.

For certain cases, contained within MMStorageSql or MMDatabaseManager, you 
could certainly write your own queries. I tried a few of those for fixing the 
balance query, but was not as successful as I had hoped. Maybe you will have 
better luck.

My schedule is pretty hectic these days, but I try to keep up on the KMM 
mailing list, especially DB related posts, as they pop up. If there is 
something more I can clarify/explain/test for you, just let me know.

-- 
Thanks,
Fernando Vilas
fvilas at iname.com
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