I'm staring at the last section of the "Advanced Associations" documentation,
which says "you can use Sequel‘s association support to get aggregate
information for columns in associated tables (sums, averages, etc.)"
Yup, that's what I want to do. But the provided example is absolutely baffling
me. Truncated code for my case as follows:
TABLE skus (
id uuid DEFAULT uuid_generate_v1() NOT NULL,
name varchar,
PRIMARY KEY (id)
);
TABLE items (
id uuid DEFAULT uuid_generate_v1() NOT NULL,
sku_id uuid NOT NULL,
quantity int4,
PRIMARY KEY (id)
);
An "item" is an invoice line item. If one row of the 'skus' table is for a
brown chair, there will be 0 or more rows in 'items' that indicate I have
sold/shipped various quantities of brown chairs to some number of people.
There's the obvious foreign key between sku_id and skus.id.
class Sku < Sequel::Model
one_to_many :items
end
class Item < Sequel::Model
many_to_one :sku
end
What I'd like to do is be able to retrieve a set of skus and the sum of the
quantity field of the associated items. In other words "Sku A, and I've shipped
xx of them. Sku B, and I've shipped yy of them," et cetera. I can certainly do
that in ways that require lots of queries, but I can't quite wrap my head
around how create the Sequel equivalent of
select skus.*, sum(items.quantity)
from skus join items on (skus.id=sku_id)
group by skus.*
which isn't actually valid SQL code, I know. It could also be
select *,
(select sum(quantity) from items where sku_id = skus.id)
from skus
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