[Dbix-class] DynamicColumns

[Ian Docherty]

Karl.

On 17 September 2012 22:20, Karl Forner <karl.forner at gmail.com> wrote:
> Hello dear DBICx users,
>
> I am currently working on a project, and I suddenly realized that I should
> have asked for your wise suggestions before
> jumping into that maybe useless project.
>
> The goal is to provide dynamic columns to dbix result objects. I was
> inspired by the DBICx::VirtualColumns package, but I do not store any value
> into the row object, just override methods that use user supplied callbacks
> to get the value.
>
> The overall intended usage is to provide some "view" columns that can be
> transparently used as is they were actual columns, for instance by
> CatalystX::ExtJS::REST
> to provide a table view of the tables that incorporate the new columns.
>
> To be more concrete, suppose that you have User table, with a foreign key
> user_type_id on a UserType table (a lookup table).
> You'd like your nice extjs grid automatically filled thanks to
> CatalystX::ExtJS::REST to display a user_type column, because the
> "user_type_id" column is not veru useful for your customers.

I did something very similar, but did not think that it warranted a
module to do it.

In my case, all I did was to add a method to the DB/Result/User.pm module

sub user_type {
    my ($self) = @_;
    return $self->user_type->name;
}

I don't think it comes much simpler than that, although for efficiency
you may want to also do a prefetch on the user_type table.

>
> Using DBICx::DynamicColumns, you could tie the (new) method/column "type" to
> $row->user_type()->name() for instance.
>
> Another intended use is to provide accessors for another project that will
> provide some optimized cache and useful accessors/checks for this kind of
> Lookup tables.
>
> I currently have a prototype that only works for one table, and that is very
> hackish because I sometimes have to hide the dynamic columns, and so wrap
> the methods that should not see those dynamic columns.
>
> What do you think ??
> Is-it a valid approach ?
>
> Thanks.
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