improvement: proper error on unsupported aggregates

lib/ash/actions/aggregate.ex

@@ -147,7 +147,7 @@ defmodule Ash.Actions.Aggregate do
                query.resource,
                name,
                kind,
-               set_opts(query, [], opts)
+               Keyword.put(set_opts(query, [], opts), :agg_name, name)
              ) do
           {:ok, aggregate} ->
             {:cont, {:ok, [aggregate | aggregates]}}
@@ -157,7 +157,12 @@ defmodule Ash.Actions.Aggregate do
         end
 
       {name, kind, agg_opts}, {:ok, aggregates} ->
-        case Ash.Query.Aggregate.new(query.resource, name, kind, set_opts(query, agg_opts, opts)) do
+        case Ash.Query.Aggregate.new(
+               query.resource,
+               name,
+               kind,
+               Keyword.put(set_opts(query, agg_opts, opts), :agg_name, name)
+             ) do
           {:ok, aggregate} ->
             {:cont, {:ok, [aggregate | aggregates]}}
 

lib/ash/actions/read/read.ex

@@ -2871,6 +2871,7 @@ defmodule Ash.Actions.Read do
              resource,
              resource_aggregate.name,
              resource_aggregate.kind,
+             agg_name: resource_aggregate.name,
              path: resource_aggregate.relationship_path,
              query: aggregate_query,
              field: resource_aggregate.field,
@@ -3125,6 +3126,7 @@ defmodule Ash.Actions.Read do
                  related_resource,
                  resource_aggregate.name,
                  resource_aggregate.kind,
+                 agg_name: resource_aggregate.name,
                  path: resource_aggregate.relationship_path,
                  query: aggregate_query,
                  field: resource_aggregate.field,

lib/ash/filter/filter.ex

@@ -2109,6 +2109,7 @@ defmodule Ash.Filter do
              resource,
              aggregate.name,
              aggregate.kind,
+             agg_name: aggregate.name,
              path: aggregate.relationship_path,
              query: aggregate_query,
              field: aggregate.field,
@@ -2808,6 +2809,7 @@ defmodule Ash.Filter do
                  context.resource,
                  aggregate.name,
                  aggregate.kind,
+                 agg_name: aggregate.name,
                  path: aggregate.relationship_path,
                  query: aggregate_query,
                  field: aggregate.field,
@@ -3162,7 +3164,7 @@ defmodule Ash.Filter do
       opts = Keyword.put(opts, :path, path)
 
       with {:ok, agg} <-
-             Ash.Query.Aggregate.new(
+             Aggregate.new(
                resource,
                agg_name(kind, opts),
                kind,
@@ -3535,6 +3537,7 @@ defmodule Ash.Filter do
                      related,
                      aggregate.name,
                      aggregate.kind,
+                     agg_name: aggregate.name,
                      path: aggregate.relationship_path,
                      query: aggregate_query,
                      field: aggregate.field,

lib/ash/query/aggregate.ex

@@ -29,7 +29,7 @@ defmodule Ash.Query.Aggregate do
   @kinds [:count, :first, :sum, :list, :max, :min, :avg, :exists, :custom]
   @type kind :: unquote(Enum.reduce(@kinds, &{:|, [], [&1, &2]}))
 
-  alias Ash.Error.Query.{NoReadAction, NoSuchRelationship}
+  alias Ash.Error.Query.{AggregatesNotSupported, NoReadAction, NoSuchRelationship}
 
   require Ash.Query
 
@@ -60,6 +60,11 @@ defmodule Ash.Query.Aggregate do
         "The relationship path to aggregate over. Only used when adding aggregates to a query.",
       default: []
     ],
+    agg_name: [
+      type: :any,
+      hide: true,
+      doc: "A resource calculation this calculation maps to."
+    ],
     query: [
       type: :any,
       doc:
@@ -180,7 +185,9 @@ defmodule Ash.Query.Aggregate do
           false
       end)
 
-    with {:ok, %Opts{} = opts} <- Opts.validate(opts) do
+    with {:ok, %Opts{} = opts} <- Opts.validate(opts),
+         agg_name = agg_name(opts),
+         :ok <- validate_supported(resource, kind, agg_name) do
       related = Ash.Resource.Info.related(resource, opts.path)
 
       query =
@@ -334,7 +341,7 @@ defmodule Ash.Query.Aggregate do
             {:ok,
              %__MODULE__{
                name: name,
-               agg_name: name,
+               agg_name: agg_name,
                resource: resource,
                constraints: constraints,
                default_value: default || default_value(kind),
@@ -367,6 +374,25 @@ defmodule Ash.Query.Aggregate do
     end
   end
 
+  defp agg_name(opts) do
+    if :agg_name in opts.__set__ do
+      opts.agg_name
+    end
+  end
+
+  defp validate_supported(resource, kind, nil) do
+    if Ash.DataLayer.data_layer_can?(resource, {:aggregate, kind}) do
+      :ok
+    else
+      {:error, AggregatesNotSupported.exception(resource: resource, feature: "using")}
+    end
+  end
+
+  # resource aggregates can only exist if supported, so we don't need to check
+  defp validate_supported(_resource, _kind, _agg_name) do
+    :ok
+  end
+
   defp parse_join_filter(resource, path, filter) do
     [last_relationship | relationships] =
       path_to_reversed_relationships(resource, path)

lib/ash/query/calculation.ex

@@ -53,7 +53,7 @@ defmodule Ash.Query.Calculation do
     calc_name: [
       type: :any,
       hide: true,
-      doc: "A resource calculation this calculation maps to. Defaults to `name`"
+      doc: "A resource calculation this calculation maps to."
     ],
     source_context: [
       type: :map,

lib/ash/query/query.ex

@@ -1628,6 +1628,7 @@ defmodule Ash.Query do
                  query.resource,
                  aggregate.name,
                  aggregate.kind,
+                 agg_name: aggregate.name,
                  path: aggregate.relationship_path,
                  query: [filter: aggregate.filter, sort: aggregate.sort],
                  field: aggregate.field,