[Dbix-class] DynamicColumns

[Ian Docherty]

On 18 September 2012 10:13, Ian Docherty <dbix-class at iandocherty.com> wrote:
> 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;
> }

Sorry. untested code. it should have been

sub user_type_name {
    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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