Storing hashes of anonymous hashes

[Mark Grant]

I have stuggled with storing hashes containing arrays and other hashes for some time now when using dbmopen() and always come up with some ugly solution that I don't like.

I want to store a hash containing an anonymous hash in a data file using "DB". This, I understand, isn't possible. However, to get around this, I have stored the code to create my "hash with anonymous hash" records as strings in another hash that is tied to the data file using the same key. I then use "eval" to set it all up.

To help explain what I am trying to achive, this code stores two hash records, each containing an anonymous hash.

%storage=();
%busses=();
use DB;

$busses{English}=( { "colour"=>"red","size"=>"big" });
$busses{Norwegian}=( { "colour"=>"green","size"=>"small" });

dbmopen %storage,"storage",0666;
foreach $i (keys %busses){
$storage{$i}="\$busses{$i}={\"colour\"=>\"$busses{$i}->{colour}\
",\"size\"=>\"$busses{$i}->{size}\"};";
}

Here is the code to retrieve a single record off of this data of the disk.

use DB;

%busses=();
%storage=();
dbmopen %storage ,"storage",0666;

$LOOKUP="Norwegian";

eval " $storage{$LOOKUP} ";

print "$LOOKUP busses are $busses{$LOOKUP}->{colour}\n";

Surprisingly, this seems to work.

My question is, is there a better, more sensible, less silly looking way of achieving this and if not, can you see any pitfalls with this approach apart fromt he waste of disk space.

Any comments appreciated.

[Mark Grant]

I perhaps should have mentioned that this is, of course, in perl :)

[H.Merijn Brand (procura · Accepted solution]

1. Do not use DB and dbmopen. That is highly deprecated
2. Use DB_File (or GDBM_File) and tie

HOH's (Hashes of Hashes) or any structure where either the key or the value is not a plain scalar cannot (directly) be stored in any of (DB|[OGN]DBM)_File

But .... we have Storable, and we have MLDBM
use http://search.cpan.org to find them

And depending on *what* is stored in the value, consider 'pack' Fast, Easy, and (once used to it) super-intuitive

use DB_File;
tie my %bus, "DB_File", "db";
$bus{Norwegian} = pack "llA10A10", $length, $height, $color, $size;

In your case Storable might be the best interface

Enjoy, Have FUN! H.Merijn

[Mark Grant]

Thanks procura.

I only started using "DB" because "DB_File" wasn't available on the box I was learning perl on :)

Looked into pack but couldn't seem to see where it would help but then forgot all about it once I had some kind of solution.

I'll look at your suggestions and be better for it!

I was just dissapointed that I couldn't find a use for "map()" in that example. Having said that, I imagine you'll turn my foreach into one.