Gossamer Forum: General: Perl Programming: Object Orientated woes

Feb 5, 2002, 7:17 AM

Wil

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Feb 5, 2002, 7:17 AM

Post #1 of 15

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Object Orientated woes

Hi

I've just finished writing a rather big module containing a lot of SQL tricks to save me some time. I'm now trying to tie this into my programs, however I'm a little consufed by this OO business.

From other modules I've seen I think I need to create a 'new' sub routine so I can call my module with something like:

Code:
use WS::MySQL; 
my $mysql = WS::MySQL->new();

The only problem is, I don't know what should go in new. I've read and heard about blessing this and belssing that but I'm still a little confused. Anyone fancy telling me what I need to put in there? At the moment, I've just got this:

Code:
sub new { 

	my $class = shift; 
	return bless {}, $class; 
}

But surely I need more than that?!

- wil

Feb 5, 2002, 7:26 AM

Paul

Veteran (19537 posts)

Feb 5, 2002, 7:26 AM

Post #2 of 15

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Re: [Wil] Object Orientated woes In reply to

It depends what options you want.

You need to return a reference so in its basic format it would be:

Code:
sub new {  
     my $self = shift; 
     return bless {}, $self;  
}

That means in your script you can do my $obj = new Module; and then you can access your method's like $obj->method

If you need more flexibility you can do something like:

Code:
sub new { 
      my $class = shift;  
      my $self = {}; 
         $self = { A => 'B', C => 'D' }; 

      return bless $self, $class; 

}

Then in your main script you can set or use those values, eg for my template parser I have a "set" key which holds the name of the template set I want to use and so in the main script I can access this value with:

$obj->{set}

...or I can change the value with $obj->{set} = 'foo';

So basically it just depends what you need.

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RedRum: Feb 5, 2002, 7:28 AM

Feb 5, 2002, 7:54 AM

Wil

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Feb 5, 2002, 7:54 AM

Post #3 of 15

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Re: [RedRum] Object Orientated woes In reply to

Hm, when I try and do that, using something like this:

Code:
	use WS::MySQL; 
	my $mysql = WS::MySQL->new(); 

	my $tbl_info = $mysql->get($dbh,"ata_members");

Code:
Can't locate object method "members" via package "WS::MySQL=HASH(0x826e650)" at index.cgi line 217.

But when I use

Code:
	my $tbl_info = WS::MySQL->get($dbh,"ata_members");

all is well, and I get no error. :-\

- wil

Feb 5, 2002, 8:14 AM

Paul

Veteran (19537 posts)

Feb 5, 2002, 8:14 AM

Post #4 of 15

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Re: [Wil] Object Orientated woes In reply to

Which new sub?....the basic one?

That error means you are missing a members() routine in WS::MySQL

Feb 5, 2002, 8:30 AM

Wil

Veteran / Moderator (4108 posts)

Feb 5, 2002, 8:30 AM

Post #5 of 15

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Re: [RedRum] Object Orientated woes In reply to

No, the sub is there. I think to bless soemthing ? Blush

- wil

Feb 5, 2002, 9:10 AM

Paul

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Feb 5, 2002, 9:10 AM

Post #6 of 15

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Re: [Wil] Object Orientated woes In reply to

What is on line 127?

You are using $mysql->get() so why is it looking for members() ?

Feb 6, 2002, 1:21 AM

Wil

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Feb 6, 2002, 1:21 AM

Post #7 of 15

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Re: [RedRum] Object Orientated woes In reply to

my $tbl_info = WS::MySQL->get($dbh,"ata_members");
my @data = $tbl_info->members("type");

I want to replace WS::MySQL in the above with $mysql->

I tried doing this by adding this line at the top:

use WS::MySQL;
my $mysql = WS::MySQL->new();

And then adding this to my WS::MySQL module:

sub new {

my $self = shift;
return bless {}, $self;
}

- wil

Feb 6, 2002, 2:24 AM

Paul

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Feb 6, 2002, 2:24 AM

Post #8 of 15

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Re: [Wil] Object Orientated woes In reply to

It should work fine although you should use

new WS::MySQL

and not

WS::MySQL->new()

Feb 6, 2002, 2:47 AM

Wil

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Feb 6, 2002, 2:47 AM

Post #9 of 15

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Re: [RedRum] Object Orientated woes In reply to

Still doesn't want to work. Thanks for trying, though.

- wil

Feb 6, 2002, 2:54 AM

Paul

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Feb 6, 2002, 2:54 AM

Post #10 of 15

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RedRum: Feb 6, 2002, 3:04 AM

Feb 6, 2002, 3:04 AM

Paul

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Feb 6, 2002, 3:04 AM

Post #11 of 15

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Re: [Wil] Object Orientated woes In reply to

Heres a quick example...pehaps you can pick it apart and get it to work in your script...

Module:

Code:
package Foo; 

sub new { return bless{}, shift } 

sub test { ref shift } 

'Foo'

Script:

Code:
#!/usr/bin/perl 

use Foo; 

print "Content-type: text/html\n\n"; 

my $obj = new Foo; 

print $obj->test;

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RedRum: Feb 6, 2002, 3:05 AM

Feb 6, 2002, 3:40 AM

Wil

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Feb 6, 2002, 3:40 AM

Post #12 of 15

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Re: [RedRum] Object Orientated woes In reply to

Hm, still can't get it to work. Here's relevant snippets from my programs, maybe you can spot what I'm doing wrong.

Code:
package WS::MySQL; 
# ------------------------------------------------------------------------ 

	use strict; 
	use DBI; 
         use vars qw/$VERSION/; # to be replaced by our in perl 5.6

	$VERSION  = 1.00; 

sub get { 
# ------------------------------------------------------------------------ 
#	Issues a SHOW COLUMNS query, and returns a reference to an 
#	object that contains the information returned by the query 
#	about the table's columns. 
# 

	my ($class, $dbh, $tbl_name) = @_; 

	# hash ref containing table information 
	my $self = {}; 

		# save table name 
		$self->{table} = $tbl_name; 

		$self->{data} = $dbh->selectall_arrayref ("SHOW COLUMNS FROM $tbl_name") 
			or die ("No information found for $tbl_name\n"); 

		# construct a row map that associates each column name with the 
		# row of SHOW COLUMNS output for that column, to make it easier 
		# to find information by column name later 

		$self->{row} = {}; 
		foreach my $row_ref (@{$self->{data}}) 
		{ 
			$self->{row}->{$row_ref->[0]} = $row_ref; 
		} 

		# bless object into class, return reference to it. 
		return (bless ($self, $class)); 

} 

sub members { 
# ------------------------------------------------------------------------ 
#	This function returns a list of legal column members. 
# 

	my ($self, $col_name) = @_; 
	my @val; 

		@val = $self->_column_info ($col_name); 

		# strip "enum(" or "set(" from beginning and ")" from end  
		# of "type" value 
		$val[1] =~ s/^[^(]*\((.*)\)$/$1/; 

		# split on commas, then trim quotes from the end of each word. 
		@val = split (/,/, $val[1]); 
		s/^'(.*)'$/$1/ foreach (@val); 

		return (@val); 

} 

sub new { 
# ------------------------------------------------------------------------ 
# 

	my $class = shift; 
	my $self = { @_ };  
	bless $self, $class; 

} 

1;

And in my script, I have:

Code:
	use WS::MySQL; 
	my $mysql = WS::MySQL->new(); 

	$dbh = $mysql->connect; # works ok

	my $tbl_info = WS::MySQL->get($dbh,"ata_members"); # works ok
	my @data = $tbl_info->members("type"); 

	my $tbl_info = $mysql->get($dbh,"ata_members"); # does not work - line 217.
	my @data = $tbl_info->members("type");

Thanks.

- wil

Last edited by:

Wil: Feb 6, 2002, 3:43 AM

Feb 6, 2002, 3:43 AM

Wil

Veteran / Moderator (4108 posts)

Feb 6, 2002, 3:43 AM

Post #13 of 15

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Re: [Wil] Object Orientated woes In reply to

Oh, and the error message I get when it dies is:

Code:
Can't locate object method "members" via package "WS::MySQL=HASH(0x82710d0)" at index.cgi line 217.

I've edited my above post to highlight line 217.

- wil

Feb 6, 2002, 4:10 AM

Paul

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Feb 6, 2002, 4:10 AM

Post #14 of 15

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Re: [Wil] Object Orientated woes In reply to

>>
my $tbl_info = $mysql->get($dbh,"ata_members"); # does not work - line 217. my @data = $tbl_info->members("type");
<<

I think line 217 is the one below the one you've indicated and the part causing the error is:

my @data = $tbl_info->members("type");

Why are you blessing in get() ?....that is the cause of the problem.

All you'd need to do is grab the table info from $obj->get() as a hashref for example:

return $self; # Not return (bless ($self, $class));

So...

my $info = $mysql->get($dbh, "ata_members");

....instead of creating another object and then you can just do:

my @data = $mysql->members("type");

There's no reason to create a second object.

Then you can do whatever you want with $info. You can access individual keys with:

my $key = $mysql->get($dbh, "ata_members")->{some_key};

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RedRum: Feb 6, 2002, 4:14 AM

Feb 6, 2002, 4:13 AM

Wil

Veteran / Moderator (4108 posts)

Feb 6, 2002, 4:13 AM

Post #15 of 15

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Re: [RedRum] Object Orientated woes In reply to

Hm, but I must have a reference to $tbl_info?

- wil