FlyingNoodle
"Computed" properties in Ash?
Does ash have the concept of “computed” fields? Ie something like
attributes do
attribute :status, :atom, constraints: [:open, :closed]
# i know this doesnt exist
computed :is_open?, :boolean, computation: expr(status == :open)
end
I’m asking because I have a calculation on a resource which is incorrect after updating the resource. Manually refetching all possible calculations seems very error prone and can’t be the recommended way. I saw in the documentation that there is a generated? setting on an attribute but the explanation Whether or not the value may be generated by the data layer. doesnt tell me too much.
My “mutation” looks like this:
ticket =
Support.Ticket.get_by_id!(ticket_id)
|> Support.Ticket.toggle!()
|> Support.load!(:is_open?)
However, this means that I would have to remember to include all the calculations that might possible be needed.
Marked As Solved
zachdaniel
I see. There are some options.
You can add a global preparation and a global change to ensure that a given calculation is always loaded, like so:
preparations do
prepare build(load: :calc)
end
changes do
change load(:calc)
end
- you can calculate the thing you need on demand:
Api.calculate(record, :is_open?)
And if you want a named function for that, you can put it in your code interface:
code_interface do
define_for YourApi
define_calculation :is_open?, args: [:_record]
end
which will give you YourResource.is_open?(your_record).
In cases where it is not necessary, this will not visit the data layer (i.e in your case we have the status, so we compute the result in Elixir). However, loading up front is often good in case calculations may need to do something expensive, you can do them in one place up front.
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