Tieing a hash to a file:   Which database format?

Posted on 2003-03-06
Medium Priority
Last Modified: 2010-03-05

I want to use persistent hash's, like with:

use DB_File;
tie(%h, 'DB_File', $Raven{'DataFile'}, O_RDWR|O_CREAT, 0666)
or die "Couldn't tie DB_file 'filename': $!; aborting";  

That uses the Berkley database thingy to tie the %h to a flat file database on disk.
It works. My problem is that I don't which, if any, database modules the client will have installed.
How do I check if each database module exists and then use that?
I thought about something like the below. Isn't there anything better? I'm not even sure
what's below would work. Just a thought.

if (eval "require DB_File") {
    use DB_File ;
    tie %h, "DB_File", "DBdb", O_RDWR|O_CREAT, 0640, $DB_HASH;
} elsif (eval "require GDBM_File") {
    use GDBM_File ;
    tie %h, 'GDBM_File', "GDBMdb", &GDBM_WRCREAT, 0640;
} elsif (eval "require NDBM_File") {
    use NDBM_File ;
    tie(%h, 'NDBM_File', 'NDBMdb', O_RDWR|O_CREAT, 0640);
} elsif (eval "require ODBM_File") {
    use ODBM_File ;
    tie(%h, 'ODBM_File', 'ODBMdb', O_RDWR|O_CREAT, 0640);
} elsif (eval "require SDBM_File") {
    use SDBM_File ;
    tie(%h, 'SDBM_File', 'SDBMdb', O_RDWR|O_CREAT, 0640);

Question by:jgore
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Accepted Solution

wilcoxon earned 300 total points
ID: 8085976
Use AnyDBM_File.  Here's an example:

    # first set the ISA to your prefered order
    @AnyDBM_File::ISA = qw(DB_File GDBM_File NDBM_File SDBM_File ODBM_File)
# now use whichever one of those is found first in your list and is present on the system
use AnyDBM_File;

Author Comment

ID: 8086245
I didn't want to add a dependency.
So, I wrote the following instead. It does the exact same thing, kinda. It seems to work. But if you see any reason
why it's not good please let me know!

use Fcntl;                                      
if (LoadDatabase==0) { print "Failed"; }
  else { print "Tied Database!"; }

# ======  LoadDatabase =================
sub LoadDatabase                                  
my @list = qw(DB_File NDBM_File GDBM_File ODBM_File SDBM_File);
my $list;

  foreach my $element (@list)
   if (eval "require $element") { @list = ($element); goto Found;}
return 0;

eval "use $list[0]";
tie (%URLHash, $list[0], "dbFileName" , O_RDWR|O_CREAT, 0640);
return 1;

Author Comment

ID: 8087188
Well, this is what I ended up with:

# =======  LoadDatabase ========
sub LoadDatabase
my @list = qw(DB_File NDBM_File GDBM_File ODBM_File SDBM_File);
my $list;

  foreach my $element (@list)
   if (eval "require $element") { @list = ($element); goto Found;}

print "Content-type: text/html\n\n<HTML><BODY>
<B>Sorry, you have no database modules installed! See instructions.</B></Body></HTML>";
die "No database modules found: DB_File NDBM_File GDBM_File ODBM_File SDBM_File";

tie %URLHash, $list[0], $Raven{'DataFile'}, O_RDWR|O_CREAT, 0640;

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