Aggregates in Ash allow for retrieving summary information over groups of related data. A simple example might be to show the "count of published posts for a user".
aggregates do count :count_of_posts, :posts, filter: [published: true] end
See the documentation for the aggregates section in
Ash.Resource.Dsl.aggregates/1 for more information.
The aggregates declared on a resource allow for declaring a set of named aggregates that can be used by extensions.
They can also be loaded in the query using
Ash.Query.load/2, or after the fact using
Ash.Api.load/3. Aggregates declared on the resource will be keys in the resource's struct.
User |> Ash.Query.new() |> Ash.Query.aggregate(:count_of_posts, :count, :posts, filter: [published: true])
See the documentation for
Ash.Query.aggregate/4 for more information.