Re: DB singleton function?

On Wednesday 27 October 2004 07:40 pm, Hans Lellelid wrote: > Hi Ian - > > >Yeah... I know how singletons work, I'm just not sure if it should connect > > to the DB or just create the instance. > > One thing related to this topic .... some APIs like mysql (is mysql the > only one?) will re-use existing connections if you pass in the same > connection parameters. > It depends on the DB driver. foo_pconnect() generally uses a persistent connection, whereas foo_connect() does not. Regardless, DB is a fairly large class, and having multiple instances of it isn't a good idea. > WI'd suggest that this behavior be avoided (by > passing a force-new-connection arg to mysql_[p]connect() method) and > that a singleton be implemented instead. Perhaps the [M]DB libs already > do this, but the reason why [M]DB does a mysql_select_db() before every > query is precisely this: that you cannot otherwise use two databases on > the same server, since the _same_ db link id would have been returned > for both connections. > Not quite sure what you mean... pconnect() should only return the same link when fed the same parameters... singleton() would act the same way, with one instance per DSN. If you call singleton() with the same DSN twice, you should get the same instance. > Yeah, anyway, I think the singleton() addition is a good idea; it's good > it exists in MDB2. Personally, I think that the name singleton() is > pretty jargon-esque, and that getInstance() might be clearer, but that's > just my opinion. > factory() is generally the method used to get a new instance; singleton() behaves differently. > I think technically the singleton implemented by MDB > (or see almost any of the core Horde classes for similar > implementations) is not a "singleton" at all since there is more than > one instance (i.e. one instance per DSN), and by definition singleton = > 1 instance. > I believe that one instance per DSN is perfectly acceptable for situations like this, and I believe that is the intent of the singleton() method in the first place.

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