On Tuesday, December 19, 2017 at 8:01:00 AM UTC-8, Alexander Popov wrote:
>
> Custom dataset methods force duplicate code.
>
Sometimes duplicate code is necessary.
> Example of desired code:
>
> Sequel::Model.plugin :dataset_associations
>
> class Area < Sequel::Model
> # has PostgreSQL `polygon`
>
> many_to_one :album
>
> one_to_many :included_locations, class: 'Location' do |ds|
> ds
> .join(
> Sequel[:areas].as(:joined_areas),
> Sequel.lit('locations.point <@ joined_areas.polygon')
> )
> .where(
> Sequel[:joined_areas][:id] =>
> defined?(id) ? id : Sequel[:areas][:id]
> )
> end
> end
>
> class Album < Sequel::Model
> # has `selling_areas` with PostgreSQL `polygon`
>
> one_to_many :selling_areas, class: Area
>
> one_to_many :potential_listeners, class: 'Listener' do |ds|
> selling_areas.included_locations.listeners
> end
>
This is probably going to break things, the block should return a modified
dataset, not a complete new dataset.
You probably want to join or use a subquery in the block, and you may want
to use the :dataset option instead of a block.
Associations can't handle every possible case. In more complex cases, you
will need to write the dataset code manually.
Thanks,
Jeremy
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