ash/documentation/topics/aggregates.md

Aggregates

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".

Declaring aggregates on a resource

Example:

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 c:Ash.Api.load/3. Aggregates declared on the resource will be keys in the resource's struct.

Custom aggregates in the query

Example:

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.