nallwhy
How to properly use aggregates on a resource?
I’m a bit stuck on how to correctly use aggregates on a resource.
Let’s say I have the following resource:
defmodule MyApp.Invoice do
use Ash.Resource
attributes do
uuid_v7_primary_key :id
attribute :amount, :decimal, allow_nil?: false
attribute :settled, :boolean, default: false, allow_nil?: false
end
end
I want to get the sum of all amounts where `settled is false, so I defined this aggregate:
aggregates do
sum :total_amount, [], :amount do
filter expr(not settled)
end
end
But:
- I’m not sure what the proper way to fetch this aggregate is.
- When I tried using
Ash.aggregate(MyApp.Invoice, {:total_amount, :sum}), it didn’t seem to apply the filter.
I’m not sure if this is a bug or if I’m misunderstanding how it’s supposed to work.
I only shared the relevant code here, but if it helps, I can create a minimal repo to reproduce it.
Thanks in advance!
Marked As Solved
zachdaniel
Ash.aggregate(Resource, {:total_amount, :sum}) should be requiring that you specify a field to be summing, i.e Ash.aggregate(Resource, {:total_amount, :sum, field: :amount}).
Ash.aggregate is for aggregating information about a query/resource as a whole. i.e
Resource
|> Ash.Query.filter(not settled)
|> Ash.aggregate(Resource, {:total_amount, :sum, field: :amount}
will get you back something like this:
{:ok, %{total_amount: #Decimal<10.0>}}, and is the “sum of of all amounts that are not settled”.
The aggregates declared in a resource are different, they are more like a calculation. They are for summary information about related data.
# on a customer resource for example
sum :total_unsettled_invoices_amount, [:invoices], :total_amount do
filter expr(not settled)
end
This allows you to say:
customer |> Ash.load!(:total_unsettled_invoices_amount)
which return something like
%Customer{total_unsettled_invoices_amount: #Decimal<10.0>}
That total_invoices_amount is “for the given customer(s), the sum of all related invoices, which are not settled”
Hopefully that helps!
Also Liked
FlyingNoodle
Aggregates are “per instance of this resource”.
I think something like this:
# in your resource
defmodule MyApp.Invoice do
actions do
read :not_settled do
filter expr(not settled)
end
end
end
# in your domain
defmodule MyApp.MyDomain do
resource MyApp.Invoice do
read :get_not_settled_invoices, action: :not_settled
end
end
# consumer
MyApp.MyDomain.get_not_settled_invoices() |> Ash.sum(:amount)
but I don’t know if thats the best way to do it? I mean you can also put this function in your domain or wherever you like.
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