in reply to Re^2: Creating an array of structures?
in thread Creating an array of structures?

Hi Tanktalus, My Advisor is not available yet today, so I haven't been able to ask further questions as to why to stay away from 2D arrays like AoA, HoA, AoH, and HoH. In the meantime I've tried to get a handle of how to populate a 2D array from results returned from a select statement run against a database. I can't quite seem to understand how to do so, I have tried many methods, but none populate the array properly. I either get a blank array or nothing happens. Below is an example of what I have thus far: 
use strict;

my ($object_name,
    $object_type,
    $module_type,
    @list_of_objects,
    $database,
    $userid,
    $passwd);

$database = 'DBI:Oracle:tdtxtasd';

print "Please enter your username:";

$userid = <STDIN>;
chomp($userid);

print "Please enter your password:";

$passwd = <STDIN>;
chomp($passwd);


use DBI;

my $dbh = DBI->connect($database, $userid, $passwd)
          or die "Couldn't connect to database: " . DBI->errstr;

my $sth = $dbh->prepare('SELECT object_name, object_type FROM user_obj
+ects WHERE object_type = ?')
                or die "Couldn't prepare statement: " . $dbh->errstr;

$module_type = "PROCEDURE";

my $rc = $sth->execute($module_type);

while (($object_name, $object_type) = $sth->fetchrow())
{
  #push @{list_of_objects},$object_name, $object_type;
  print "$object_name $object_type\n";
};

$dbh->disconnect;

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I know the "#push @{list_of_object},$object_name, $object_type;" line is wrong, but am not sure how to populate what I want to be a 2D array (@list_of_objects) with the two variables returned for each row ($object_name and $object_type). Additionally, once this occurs, how will I be able to reference just the $object_name from this array for each element in the array to then search a document for each $object_name. Is it a case of using foreach loops to reference each dimension in the array? Such as(extreme pseudocode to follow: 
foreach i (1....n)
{
  foreach j (1,2)
  {
     $object_name = @list_of_values[i][2];
  }
};

[download]
I realize this is a long post. I hope I get my point across. Let me know what you think. Thanks.

Replies are listed 'Best First'.
Re^4: Creating an array of structures?
by Tanktalus (Canon) on Mar 08, 2005 at 18:24 UTC

    I'll embed some comments in your code.

    # good idea :-)
use strict;

# There are many theories on why this is a bad idea.
# My personal favourite is keeping the scope of a variable
# as small as possible.  Larger scope means that when I'm
# trying to read your code, I need to go back farther in
# the program to find out it's a lexical, and to find out
# who may have changed the value.
# Another reason I know to change this is to create and initialise
# the variable at the same time - it means having no undef
# variables (unless you explicitly want it to be undef).
# For example, there is no reason to have $database undefined.
# That would be an error.  By combining the my with the
# initialisation, then there is no point in the program
# where you could be accessing an undefined $database.
#my ($object_name,
#    $object_type,
#    $module_type,
#    @list_of_objects,
#    $database,
#    $userid,
#    $passwd);

# create/initialise.
my $database = 'DBI:Oracle:tdtxtasd';

print "Please enter your username:";

my $userid = <STDIN>;
chomp($userid);

print "Please enter your password:";

# You can super-search on passwords - there are ways to
# do this without echoing to the screen.  I think it's
# in code snippets - and I think I contributed to it ;-)
my $passwd = <STDIN>;
chomp($passwd);

# some people put all use's at the top.  Some put them
# close to where they're used.  I'm not convinced one is
# better than the other, so this is just FYI.
use DBI;

# here's a my which initialises.  Good choice :-)
my $dbh = DBI->connect($database, $userid, $passwd)
          or die "Couldn't connect to database: " . DBI->errstr;

my $sth = $dbh->prepare('SELECT object_name, object_type FROM user_obj
+ects WHERE object_type = ?')
                or die "Couldn't prepare statement: " . $dbh->errstr;

my $module_type = "PROCEDURE";

my $rc = $sth->execute($module_type);

my @list_of_objects;
while (($object_name, $object_type) = $sth->fetchrow())
{
  print "$object_name $object_type\n";
  # push a scalar onto the list.  That scalar is an array ref.
  # in this case, a ref to an anonymous array.
  push @list_of_objects, [ $object_name, $object_type ];
};

$dbh->disconnect;

    [download]
    To read it back out: 
    foreach my $object (@list_of_objects)
{
  my @values = @{$object};
  # do whatever.
}

    [download]
    Hope that helps!

[reply]
[d/l]
[select]

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