Re: Is there a module that provides an abstract record class?

On Fri, 29 Mar 2013 05:17:58 -0600, Tom Christiansen <tchrist@perl.com>
wrote:

> Hey guys,
> 
> My CPAN search-fu seems to be flagging, because I cannot find something
> that surely must exist, and it seems a shame to re-implement a perfectly
> functioning wheel if it already exists and I just don't know about it.
> 
> I wondered whether you knew of a somewhat generic, plug-in-able frameworky
> class that allows you to read structured records from files of various
> formats in a uniform fashion, and treat those records the same way using
> some common interface.  I'm betting it must already exist, but I could
> find nothing on CPAN that seemed at all like what I am thinking of.
> 
> Ring any bells?
> 
> Details follow. . . .
> 
> The idea is that you would have to associate some other class with the
> handle/file, one that knew the actual guts, and then call some special
> record reading method:
> 
>     $rec_obj = read_record($handle)
> 
> or even convert an existing string into one of these objects:
> 
>     $rec_obj = string2record(RAW => $string, RECTYPE => "some type");
> 
> Just to use simple, at-hand examples:
> 
> 1.  open(my $handle, "<", "/etc/passwd");
>     my$fmt_obj = fetch_format("passwd"); # maybe type IO::Record::passwd
>     while (my $r = $fmt_obj->read_record($handle)) { 
> 	printf "%s uses %s\n", $r->{user}, $r->{shell};
> 	print "pwent is $r\n";
>     }
> 
> 
> 2.  open(my $handle, "< :raw :bytes", "/var/run/utmp");
>     my $fmt_obj = fetch_format("utmp"); # maybe type IO::Record::utmp
>     while (my $r = $fmt_obj->read_record($handle)) { 
> 	printf "%s is from %s\n", $r->{name}, $r->{user};
> 	print "utmp entry is $r\n";
>     }
> 
> 
> 3.  open(my $handle, "<", "/etc/termcap");
>     my $fmt_obj = fetch_format("termcap");  # maybe type IO::Record::termcap
>     while (my $r = $fmt_obj->read_record($handle)) { 
> 	printf "tcap ent %s uses %s and %s for stand-out pairs\n", 
> 	    $r->{name}, $r->{so}, $r->{se};
> 	my @fieldnames = $f->fields();  # this is ordered, and might have dups
> 	printf "tcap ent %s has fields %s\n", 
> 	    $r->{name}, join("," => @fieldnames);
>     }
> 
> The point is that once you can identify the *type* of the file's records,
> there can be some dedicated subclass that knows how to get that particular
> record format into some generic interface so that you can work with it
> in a reasonably uniform way.
> 
> The reason I would like this is because I have already written a working
> prototype of a program that essentially works this way:
> 
>     % pwgrep '$gcos !~ /daemon/i && $shell !~ /sh\b/'  /etc/passwd
> 
> which is really nothing more than this sort of thing:
> 
>     % recgrep --rectype=passwd -e '$gcos !~ /daemon/i && $shell !~ /sh\b/' /etc/passwd
> 
> And I would like a nice generic approach to adding new record types.  The
> existing program has a hardcoded list of types, and that isn't how I want
> to go with this.  I want to be able to provide little, extensible
> per-record subclasses that inherit from a common class that provides the
> defined interface.  The idea is to write as little new as possible when
> defining a new record type.
> 
> This isn't actually for sysadmin files, but rather for a bunch of different
> kinds of record types, some binary, some not, some multiline, some not,
> some splittable and some unpackable, some with duplicate field names, some
> not, &c &c &c.
> 
> Do you happen to know any existing module that addresses this sort
> of record-based activity in some sort of a generic way?
> 
> Note that I am *not* asking about the namespace games and eval/precompile
> bit of the recgrepper.  I certainly know how to do that, and it works
> just fine right now (there are @foo for dup fieldnames, BTW).  Rather, 
> it is this sort of thing:
> 
>     my $fmt_obj = fetch_format("arbitrary name");  
>     my $rec_obj = $fmt_obj->read_record($handle);
> 
> that I am looking to piggy-back on existing work for.  But I know of 
> none such out there.  Anybody heard of anything like this?

Does DBD::AnyData come close enough?

-- 
H.Merijn Brand  http://tux.nl   Perl Monger  http://amsterdam.pm.org/
using perl5.00307 .. 5.17   porting perl5 on HP-UX, AIX, and openSUSE
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• Is there a module that provides an abstract record class? by Tom Christiansen
• Re: Is there a module that provides an abstract record class? by Sébastien Aperghis-Tramoni
• Re: Is there a module that provides an abstract record class? by H.Merijn Brand
• Re: Is there a module that provides an abstract record class? by Tom Christiansen
• Re: Is there a module that provides an abstract record class? by Sven Dowideit