feat(import): resolve import group and fee-type names against existing records

test/mv/membership/import/column_resolver_query_test.exs

@@ -0,0 +1,72 @@
+defmodule Mv.Membership.Import.ColumnResolverQueryTest do
+  # async: false — attaches a global telemetry handler to inspect emitted SQL.
+  use Mv.DataCase, async: false
+
+  alias Mv.Membership.Import.ColumnResolver
+
+  setup do
+    %{actor: Mv.Helpers.SystemActor.get_system_actor()}
+  end
+
+  describe "create_or_find_group/3 group lookup is name-filtered (no full-table scan)" do
+    test "resolving a new name absent from the snapshot queries by name, not the whole table",
+         %{actor: actor} do
+      # Populate the table so a full-table read would be costly and observable.
+      for n <- 1..20, do: Mv.Fixtures.group_fixture(%{name: "Existing #{n}"})
+
+      queries =
+        capture_group_select_queries(fn ->
+          # The name is absent from the (empty) snapshot, forcing a DB lookup
+          # before the create attempt. That lookup must filter by name.
+          assert {:ok, group} = ColumnResolver.create_or_find_group("New One", [], actor)
+          assert group.name == "New One"
+        end)
+
+      # No SELECT against the groups table issued during resolution may be an
+      # unfiltered full-table scan. The pre-create existence check must filter by
+      # name (carry a WHERE predicate).
+      refute Enum.any?(queries, &unfiltered_groups_select?/1),
+             "expected no unfiltered groups table scan, got:\n#{Enum.join(queries, "\n")}"
+    end
+  end
+
+  defp capture_group_select_queries(fun) do
+    test_pid = self()
+    handler_id = "test-group-query-#{System.unique_integer([:positive])}"
+
+    :telemetry.attach(
+      handler_id,
+      [:mv, :repo, :query],
+      fn _event, _measurements, metadata, _config ->
+        sql = metadata[:query] || ""
+
+        if String.contains?(sql, "SELECT") and String.contains?(sql, "\"groups\"") do
+          send(test_pid, {:group_query, sql})
+        end
+      end,
+      nil
+    )
+
+    try do
+      fun.()
+    after
+      :telemetry.detach(handler_id)
+    end
+
+    collect_group_queries([])
+  end
+
+  defp collect_group_queries(acc) do
+    receive do
+      {:group_query, sql} -> collect_group_queries([sql | acc])
+    after
+      0 -> Enum.reverse(acc)
+    end
+  end
+
+  # An unfiltered groups SELECT reads the whole table: it selects FROM "groups"
+  # with no WHERE clause at all. A name-filtered lookup carries a WHERE predicate.
+  defp unfiltered_groups_select?(sql) do
+    String.contains?(sql, "FROM \"groups\"") and not String.contains?(sql, "WHERE")
+  end
+end