[PATCH] Re: Class::DBI::Loader and the CDBI inheritance hierarchy

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Kingsley Kerce writes:
 > Consider the familiar CD schema in the SYNOPSIS of the Class::DBI POD.
 > Focusing on the Music::Artist class, and supposing we include a
 > retrieve_all method in our "top level" class Music::DBI to override
 > Class::DBI's retrieve_all method, we end up with the following
 > inheritance hierarchy.
 > (note: ASCII art ahead -- view in fixed-width font)
 > 
 > Class::DBI
 >       retrieve_all
 >     |
 >     |
 > Music::DBI
 >       retrieve_all
 >     |
 >     |
 > Music::Artist
 > 
 > As expected, invoking Music::Artist->retrieve_all will execute the
 > Music::DBI retrieve_all method.
 > 
 > Now, if we instead use Class::DBI::Loader (a relatively recent
 > version) to set up the Music::Artist class, and -- just for purposes
 > of being specific in this example -- suppose we use an SQLite
 > datasource, we end up with a different inheritance hierarchy.
 > In particular, Music::Artist has had Class::DBI::SQLite included in
 > its @ISA (see the Class-DBI-Loader-0.17 distribution, file
 > Class/DBI/Loader/Generic.pm, line 179, for when this occurs).
 > 
 > 
 >                Class::DBI
 >              /       retrieve_all
 >            /             \
 >          /                 \
 > Class::DBI::SQLite          Music::DBI                
 >                                   retrieve_all
 >          \                  /
 >            \              /
 >              \          /
 >              Music::Artist
 > 
 > In this case, invoking Music::Artist->retrieve_all will execute the
 > Class::DBI retrieve_all method.  This seems to not be a good thing.
 > Am I missing something here?  Is it really necessary for CDBIL to muck
 > with @Music::Artist::ISA?
 > 
 > Thanks,
 > Kings

To avoid any diamond inheritance issues, CDBIL should temporarily --
not permanently -- modify the ISA of a table class.
Patch below.

Kings

$ diff -Bub Class-DBI-Loader-0.17/lib/Class/DBI/Loader/{Generic.pm.orig,Generic.pm}
--- Class-DBI-Loader-0.17/lib/Class/DBI/Loader/Generic.pm.orig  Fri Mar 11 19:59:45 2005
+++ Class-DBI-Loader-0.17/lib/Class/DBI/Loader/Generic.pm       Fri Mar 25 13:03:23 2005
@@ -176,9 +176,10 @@
         my $class = $self->_table2class($table);
         warn qq/Initializing "$class"/ if $self->debug;
         no strict 'refs';
-        @{"$class\::ISA"} = $db_class;
+        push @{"$class\::ISA"}, $db_class;
         $class->set_db( Main => @{ $self->{_datasource} } );
         $class->set_up_table($table);
+        @{"$class\::ISA"} = grep { $_ ne $db_class } @{"$class\::ISA"};
         $self->{CLASSES}->{$table} = $class;
         my $code = "package $class;$additional_base$additional";
         warn qq/Additional classes are "$code"/ if $self->debug;