hashes frustration

ant has asked for the wisdom of the Perl Monks concerning the following question:

I am currently reading about the Perl DBI module, and the first chapter explained about the Berkley DB_File and tieing hashes to a file. I followed the example from the book and succesfully got it working. However I then wrote a method that would return a particular part of a string thus (main parts of code) my $db = tie %database, 'DB_File', "simpleinsert.dat",O_CREAT | O_RDWR, 0666 or die "Cannot initialise database"; $database{'anthony1'}=new contacts_db('anthony', 'ant@hot', '14 road', '102892', '34567')->pack(); I can then access the name by my $person = new contacts_db($database{'anthony1'}); $person->unpack_name(); this then returns 'anthony'. but if i put $database{'anthony1'}->unpack_name(); nothing is brought back, why??????????

Comment on hashes frustration

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(jcwren) Re: hashes frustration by jcwren (Prior) on Sep 14, 2000 at 18:07 UTC
I haven't used DB_File, but I was playing with tied hashes in relation to Config::IniFiles and through a combination of not understanding the limitations of tied hashes and questionable documentation in the module, was having a problem. After corresponding with the author of the module, who had an incomplete picture of auto-vivification, he referred me to this link, and in particular Limitation #3. If you get to where you're trying to do something like this, perhaps this will save you some time. http://aut.dk/orqwood/dwh/dwh_pod.html (For all I know, this may be common knowledge. But it helped me, so pass it on I shall. Also, the module tis article refers to DWH_File seems like it could be useful.) --Chris e-mail jcwren	[reply]
Re-post: hashes frustration by cwest (Friar) on Sep 14, 2000 at 17:38 UTC
I am currently reading about the Perl DBI module, and the first chapter explained about the Berkley DB_File and tieing hashes to a file. I followed the example from the book and succesfully got it working. However I then wrote a method that would return a particular part of a string thus (main parts of code) `my $db = tie %database, 'DB_File', "simpleinsert.dat",O_CREAT \| O_RDWR +, 0666 or die "Cannot initialise database"; $database{'anthony1'}=new contacts_db('anthony', 'ant@hot', '14 road', '102892', '34567')->pack();` [download] I can then access the name by `my $person = new contacts_db($database{'anthony1'}); $person->unpack_name();` [download] this then returns 'anthony'. but if i put `$database{'anthony1'}->unpack_name();` [download] nothing is brought back, why?????????? -- Casey I am a superhero.	[reply] [d/l] [select]
RE: Re-post: hashes frustration by Perlmage (Acolyte) on Sep 14, 2000 at 18:23 UTC
You're not putting an object in the hash, so you can't call a method on it later. What you're actually doing is calling a class method on the package that corresponds to whatever pack() returns. The first form works because you are re-blessing the packed version into the class that contains the unpack_name() method. I'm not sure why the second form works at all without resulting in an error, actually. There are modules on the CPAN that will let you tie() a hash to a database and then store and fetch references (including blessed ones) from them, or you could roll your own with Storable or FreezeThaw or the like.	[reply]
RE: Re-post: hashes frustration by cwest (Friar) on Sep 14, 2000 at 17:42 UTC
I haven't used DB_Files but this is my guess: try: `(contacts_db($database->{anthony1}))->unpack_name()` [download] Since contacts_db() returns a reference for you to unpack_name() with, you can simplify this into one statement like the above. It's untested, but I'm 74.2% sure it will work. -- Casey I am a superhero.	[reply] [d/l]


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