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Dogma has asked for the wisdom of the Perl Monks concerning the following question:
This is a follow up to my prevous posting CGI Design
Following the wonderful advice of Ovid I have moved his code example into my CGI script. So I went from this quickly growing IF/THEN/ELSE constuct...
if (defined($q->param())) {
if ($q->param('action') eq 'add') {
if ($q->param('confirm')) {
if ($q->param('commit')) {
&commit_dialog();
} else {
&confirm_dialog();
}
} else {
&add_dialog();
}
} elsif ($q->param('action') eq 'remove') {
if ($q->param('confirm')){
if ($q->param('commit')) {
&commit_dialog();
} else {
&confirm_dialog();
}
} else {
&choose_dialog();
}
} elsif ($q->param('action') eq 'modify') {
if ($q->param('confirm')) {
if ($q->param('commit')) {
&commit_dialog();
} else {
&confirm_dialog();
}
} else {
&choose_dialog();
}
} else {
&action_dialog();
}
} else {
&action_dialog();
}
To this rather cleaner Dispatch table from Ovid...
sub get_branch_function {
my $query = shift;
my $action = $query->param('action') || 0;
my $confirm = $query->param('confirm') ? 1 : 0;
my $commit = $query->param('commit') ? 1 : 0;
my %dispatch = (
add => {
confirm => {
commit => \&commit_dialog,
default => \&add_dialog,
},
default => \&add_dialog,
},
remove => {
confirm => {
commit => \&commit_dialog,
default => \&confirm_dialog,
},
default => \&choose_dialog,
},
modify => {
confirm => {
commit => \&commit_dialog,
default => \&confirm_dialog,
},
default => \&choose_dialog,
},
default => \&action_dialog
);
if ( ! exists $dispatch{ $action } ) {
return $dispatch{ default }
} elsif ( ! $confirm ) {
return $dispatch{ $action }{ default };
} elsif ( ! $commit ) {
return $dispatch{ $action }{ confirm }{ default };
} else {
return $dispatch{ $action }{ confirm }{ commit };
}
}
Unfortunately this will only work if all actions have the same depth in the dispatch table. I need one of my actions to have an extra step.
my %dispatch = (
add => {
confirm => {
commit => \&commit_dialog,
default => \&confirm_dialog,
},
default => \&update_dialog,
},
remove => {
confirm => {
commit => \&commit_dialog,
default => \&confirm_dialog,
},
default => \&choose_dialog,
},
modify => {
update => {
confirm => {
commit => \&commit_dialog,
default => \&confirm_dialog,
},
default => \&update_dialog,
},
default => \&choose_dialog,
},
default => \&action_dialog
);
So I am again faced with replacing the simple logic in my (Ovid's) dispatch code with a large IF/THEN/ELSE.
sub dispatch_table {
my $q = shift;
my $action = $q->param('action') || 0;
my $confirm = $q->param('confirm') ? 1 : 0;
my $commit = $q->param('commit') ? 1 : 0;
my $update = $q->param{'update') ? 1 : 0;
my %dispatch = (
add => {
confirm => {
commit => \&commit_dialog,
default => \&confirm_dialog,
},
default => \&update_dialog,
},
remove => {
confirm => {
commit => \&commit_dialog,
default => \&confirm_dialog,
},
default => \&choose_dialog,
},
modify => {
update => {
confirm => {
commit => \&commit_dialog,
default => \&confirm_dialog,
},
default => \&update_dialog,
},
default => \&choose_dialog,
},
default => \&action_dialog
);
if (! exists $dispatch{$action}) {
return $dispatch{default}
} elsif (! $confirm) {
return $dispatch{$action}{default};
} elsif (! $commit) {
return $dispatch{$action}{confirm}{default};
} else {
return $dispatch{$action}{confirm}{commit};
}
}
Am I still just not getting it? I had lots of responses to my first question suggesting I move to CGI::Application. Which I may still do but I'd like to beable to solve this with using another module. I am willing to provide the entire CGI by emai/etc because it is rather large to be posting here. Any suggestions?
Thanks,
-Dogma
Edit by tye (added <readmore>, "fixed" link) |
Re: Improved CGI Design
by Fletch (Bishop) on Apr 09, 2002 at 02:18 UTC
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Make an array of actions. Pop off the first item and
use that to determine the first level sub to call. Pass
that first level call the rest of the actions to be executed.
Lather, rinse, repeat.
Update: After thinking about it more, this seems
similar to the chapter on multiple dispatch in Object Oriented Perl. If you have access to a copy, check
it out (chapter 14 or 15, IMSMR) and see if it offers any
enlightenment.
| [reply] |
Re: Improved CGI Design
by George_Sherston (Vicar) on Apr 09, 2002 at 13:34 UTC
|
Strikes me that what you have at the moment is a combination of dispatch table and if/else tree. I have tended to go with pure if/else trees because I find them easy to get my head round. But this thread stimulated me to think through dispatch tables again. My suggestion wd be to fill out the hash with default values, so that for every possible combination of keys there is a value. I'd then make the variables you set up at the beginning return keys (in fact you could cut out that step altogether by making the form send the keys - but I agree it's a good idea to have that step in case someone changes the form). If you did that then I *think* you could cut out the if/else altogether (but I should add that I haven't tested the below code - it will in any event suffice to show what I'm talking about).
sub get_branch_function {
my $query = shift;
# get all three levels of keys into variables,
# setting defaults as necessary:
my $action = $query->param('action') ? $query->param('action') :
+'default';
my $confirm = $query->param('confirm') ? 'confirm' : 'default';
my $commit = $query->param('commit') ? 'commit' : 'default';
# set up the hash so that whatever combination of keys
# it gets, it will produce a value:
my %dispatch = (
add => {
confirm => {
commit => \&commit_dialog,
default => \&add_dialog,
},
default => {
commit => \&add_dialog,
default => \&add_dialog,
},
},
remove => {
confirm => {
commit => \&commit_dialog,
default => \&confirm_dialog,
},
default => {
commit => \&choose_dialog,
default => \&choose_dialog,
},
},
modify => {
confirm => {
commit => \&commit_dialog,
default => \&confirm_dialog,
},
default => {
commit => \&choose_dialog,
default => \&choose_dialog,
},
},
default => {
confirm => {
commit => \&action_dialog,
default => \&action_dialog,
},
default => {
commit => \&action_dialog,
default => \&action_dialog,
},
},
);
# now one step should return the right subroutine:
return $dispatch{ $action }{ $confirm }{ $default };
}
I agree that this makes the hash bigger; but it should not be much of a resource drain since the extra values are references; and I find the regular structure of the hash makes it easier to see what goes on.
§ George Sherston | [reply]
[d/l] |
|
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That is another way of implimenting the dispatch table however that really doesn't help me in thie situation. I need to have one of the hash entries be "deeper" then the rest. Your example is basicly what I already have - a table that works if all entries have the same depth. Although it does help simplify the IF/THEN/ELSE that is remaing.
Cheers,
-Dogma
| [reply] |
|
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Yes, I see. I suppose the logic of my approach is to add another level *throughout* the hash. Then it does get quite big, though it also remains logical and regular in a slightly obsessive-compulsive way. Untested:
sub get_branch_function {
my $query = shift;
my $action = $query->param('action') ? $query->param('action') :
+'default';
my $update = $query->param('update') ? 'update' : 'default';
my $confirm = $query->param('confirm') ? 'confirm' : 'default';
my $commit = $query->param('commit') ? 'commit' : 'default';
my %dispatch = (
add => {
update => {
confirm => {
commit => \&commit_dialog,
default => \&add_dialog,
},
default => {
commit => \&add_dialog,
default => \&add_dialog,
},
},
default => {
confirm => {
commit => \&commit_dialog,
default => \&add_dialog,
},
default => {
commit => \&add_dialog,
default => \&add_dialog,
},
},
},
remove => {
update => {
confirm => {
commit => \&commit_dialog,
default => \&confirm_dialog,
},
default => {
commit => \&choose_dialog,
default => \&choose_dialog,
},
},
default => {
confirm => {
commit => \&commit_dialog,
default => \&confirm_dialog,
},
default => {
commit => \&choose_dialog,
default => \&choose_dialog,
},
},
},
modify => {
update => {
confirm => {
commit => \&commit_dialog,
default => \&confirm_dialog,
},
default => {
commit => \&choose_dialog,
default => \&choose_dialog,
},
},
default => {
confirm => {
commit => \&choose_dialog,
default => \&choose_dialog,
},
default => {
commit => \&choose_dialog,
default => \&choose_dialog,
},
},
},
default => {
update => {
confirm => {
commit => \&action_dialog,
default => \&action_dialog,
},
default => {
commit => \&action_dialog,
default => \&action_dialog,
},
},
default => {
confirm => {
commit => \&action_dialog,
default => \&action_dialog,
},
default => {
commit => \&action_dialog,
default => \&action_dialog,
},
},
},
);
return $dispatch{ $action }{ $update }{ $confirm }{ $commit };
}
§ George Sherston | [reply]
[d/l] |
Re: Improved CGI Design
by Chmrr (Vicar) on Apr 09, 2002 at 21:42 UTC
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Use a loop to march through your table; untested code below, but it should get you started.
sub dispatch_table {
my $q = shift;
my %dispatch = (
add => {
confirm => {
commit => \&commit_dialog,
default => \&confirm_dialog,
},
default => \&update_dialog,
},
remove => {
confirm => {
commit => \&commit_dialog,
default => \&confirm_dialog,
},
default => \&choose_dialog,
},
modify => {
update => {
confirm => {
commit => \&commit_dialog,
default => \&confirm_dialog,
},
default => \&update_dialog,
},
default => \&choose_dialog,
},
default => \&action_dialog
);
for (qw/action confirm commit update/) {
if (! exists $dispatch{$q->param($_)}) {
return $dispatch{default};
} else {
my $ref = $dispatch{$q->param($_)};
if (ref $ref eq "CODE") {
return $ref;
} elsif (ref $ref eq "HASH") {
%dispatch = %{$ref};
} else {
die "Our dispatch hash is messed up."
}
}
}
return $dispatch{default};
}
perl -pe '"I lo*`+$^X$\"$]!$/"=~m%(.*)%s;$_=$1;y^`+*^e v^#$&V"+@( NO CARRIER' | [reply]
[d/l] |
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