Class::DBI many to many delete

CassJ has asked for the wisdom of the Perl Monks concerning the following question:

Hi Monks, Using CDBI, I have the following relationships defined:

WebR::M::CDBI::DatatypeRelationship->has_a(parent=>'WebR::M::CDBI::Dat
+atype');

WebR::M::CDBI::DatatypeRelationship->has_a(child=>'WebR::M::CDBI::Data
+type');    

WebR::M::CDBI::Datatype->has_many(parents=>['WebR::M::CDBI::DatatypeRe
+lationship'=> 'parent'], 'child');    

WebR::M::CDBI::Datatype->has_many(children=>['WebR::M::CDBI::DatatypeR
+elationship'=>'child'], 'parent');
[download]

When I try to delete a datafile, the cascade delete appears to work for the entries in the relationship table where that datafile is parent, but not where it is child. I had assumed that both would be deleted. Is this how it's supposed to work? Am I missing something obvious? Thanks, Cxx

Comment on Class::DBI many to many delete Download Code

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Re: Class::DBI many to many delete by Khen1950fx (Canon) on Jul 17, 2006 at 23:03 UTC
It should work. According to the docs, the default for cascading delete is to delete the child if the parent is deleted; but it's not working here. So, we have to work around it. Class::DBI doesn't support Many to Many right now. The module's author does say that you can manually set up the relationships and get some measure of control by writing a Class::DBI::Cascade::Plugin::Nullify and inserting it into the relationship: `WebR::M::CDBI::Datatype->has_many(children=>['WebR::M::CDBI::DatatypeR +elationship'=>'child"], 'parent', { cascade => 'Class::DBI::Cascade::Plugin::Nullify' });` [download] Try it and see if that works. I hope this helps.	[reply] [d/l]
Re^2: Class::DBI many to many delete by CassJ (Sexton) on Jul 18, 2006 at 00:12 UTC
Odd. This works fine: `WebR::M::CDBI::DatafileRelationship->has_a(child=>'WebR::M::CDBI:: +Datafile'); WebR::M::CDBI::DatafileRelationship->has_a(parent=>'WebR::M::CDBI: +:Datafile'); WebR::M::CDBI::Datafile->has_many(parents=>['WebR::M::CDBI::Datafi +leRelationship' => 'parent'],'child', { cascade => 'Class::DBI::Cascade::Delete'}); WebR::M::CDBI::Datafile->has_many(children=>['WebR::M::CDBI::Dataf +ileRelationship' => 'child'],'parent', { cascade => 'Class::DBI::Cascade::Delete'} );` [download] Ah - and if I do `WebR::M::CDBI::DatafileRelationship->has_a(child=>'WebR::M::CDBI:: +Datafile', {cascade=>'Class::DBI::Cascade::Delete'});` [download] then the child datafiles get deleted too. Great! thanks! And, for the has_many relationships where I just want the FK to be nulled, rather than the record deleted: `package Class::DBI::Cascade::Nullify; use base 'Class::DBI::Cascade::None'; use Data::Dumper; sub cascade { my ($self, $obj) = @_; my $fk =$self->{_rel}->args->{foreign_key}; foreach ($self->foreign_for($obj)){ $_->$fk(undef); $_->update; } } 1;` [download]	[reply] [d/l] [select]
Re: Class::DBI many to many delete by perrin (Chancellor) on Jul 17, 2006 at 15:39 UTC
That looks like it should work. Do you get any errors, or does it just not delete them?	[reply]
Re^2: Class::DBI many to many delete by CassJ (Sexton) on Jul 17, 2006 at 23:49 UTC
No errors. It just doesn't delete. I'll go investigate further. I just wanted to be sure I hadn't misunderstood the expected behaviour, before I spend ages digging around working out what else could be broken.	[reply]