Hi Andreas,
On Mon, 16 Mar 2009, Andreas Mock wrote:
Hi all,
as part of another thread I want to extract the following question with a more
meaningful subject:
We do have objects (O) which consist of attribues (A) which are
stored in a table O with columns A just as DBIC would model it.
But we do also have sparse attributes (B) (attributes which are very often
NULL) which are not stored as columns of the "base" table O but as rows
of a - let's call it attribute table - where each "not null"-attribut B of O is
a
row in that table with a key consisting of a class identifier,
an object identifier (O.id) and an attribute identifier.
Some diagrams would go a long way to explaining whats going on there.. let
me take some guesses:
Table O:
ID | colour | attr2
----------------------
1 | red | 2
2 | orange | 4
3 | yellow | 6
Table Attribute:
O_id | Class | Value
----------------------
1 | length | 3cm
1 | height | 4cm
3 | length | 2cm
Anywhere close?
After loading this object I want to see that object in a flat way. This
"attribute collection" shall show up as "normal" (columns) attributes
(with accessors named like the attribute identifier).
While using the object from the application perspective I don't want to
know that there are some attributes stored as columns in the base table
and some as entries in a related table.
And you'd like:
my $row1 = $schema->resultset('O')->find(1);
$row1->colour - returns red
$row1->length - returns '3cm'
which in normal dbic would be:
$row1->attributes->find({ Class => 'length'})->Value
Is there a way in DBIC to do this?
There's always a way.. You can add more logic to your O class, so that its
transparent to the rest of the system.
Is there a table which defines which classes of attributes can exist?
Without that, anyone could put any string in there, which makes adding
accessors tricky. Even then, if someone adds a new one..
I think you'll need autoload in your O clas, aka:
sub AUTOLOAD {
my $self = shift;
my $attr_name = $AUTOLOAD;
$attr_name =~ s/.*://;
my $attr = $self->attributes->find({ class => $attr_name });
die "No such attribute $attr_name" if(!$attr);
return $attr->value;
}
Not convinced this is the best solution.. maybe someone will come up with
a better one now I've suggested it!
Jess
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