Reporter#moab_detail_csv_list: even fewer queries to run

now instead of querying for the CompleteMoabs for each PreservedObject, leverage the fact that the query already gets most of that info, with the exception of the name of the from_moab_storage_root for each CompleteMoab.  since there are only 10s of storage roots in prod, and since the names are very stable, it's much cheaper to look up each of those names once and cache the result.  we already have the current storage root name in the MoabStorageRoot ivar.  bonus:  easier to get at the column values we want by using #each_row to get a hash, and also no extraneous ActiveRecord objects to instantiate (downside: manual translation of status enum values)

app/services/reporter.rb

@@ -12,9 +12,10 @@ class Reporter
   # @return [Reporter] the reporter
   def initialize(params)
     @storage_root = MoabStorageRoot.find_by!(name: params[:storage_root_name])
+    @msr_names = {}
   end
 
-  def moab_storage_root_list_preserved_objects_relation
+  def moab_storage_root_list_pres_obj_comp_moabs_relation
     PreservedObject
       .joins(:complete_moabs)
       .where(complete_moabs: { moab_storage_root: storage_root })
@@ -24,7 +25,7 @@ def moab_storage_root_list_preserved_objects_relation
   # @return [Array] an array of druids on the storage root
   def druid_csv_list
     druid_array = [['druid']]
-    moab_storage_root_list_preserved_objects_relation
+    moab_storage_root_list_pres_obj_comp_moabs_relation
       .select(:druid)
       .each_row do |po_hash|
         druid_array << [po_hash['druid']]
@@ -35,22 +36,36 @@ def druid_csv_list
   # @param [Boolean] errors_only (default: false) - optionally only output lines with audit errors
   # @return [Array] an array of hashes with details for each druid provided
   def moab_detail_csv_list(errors_only: false)
-    query = if errors_only
-      moab_storage_root_list_preserved_objects_relation.where.not(complete_moabs: { status: 'ok' })
-    else
-      moab_storage_root_list_preserved_objects_relation
-    end
-
-    detail_array = [['druid', 'from_storage_root', 'storage_root', 'last_checksum_validation', 'last_moab_validation', 'status', 'status_details']]
-    query.each_instance do |preserved_object|
-      preserved_object.complete_moabs.each do |cm|
-        detail_array << [
-          preserved_object.druid, cm.from_moab_storage_root&.name, cm.moab_storage_root.name,
-          cm.last_checksum_validation, cm.last_moab_validation, cm.status, cm.status_details
-        ]
+    query =
+      if errors_only
+        moab_storage_root_list_pres_obj_comp_moabs_relation.where.not(complete_moabs: { status: 'ok' })
+      else
+        moab_storage_root_list_pres_obj_comp_moabs_relation
       end
+
+    header_row = [['druid', 'from_storage_root', 'storage_root', 'last_checksum_validation', 'last_moab_validation', 'status', 'status_details']]
+
+    # cols doesn't include storage_root name (available via storage_root ivar).  also we're not instantiating AR objects, so we have to translate
+    # the underlying status enum
+    cols = ['druid', 'from_moab_storage_root_id', 'last_checksum_validation', 'last_moab_validation', 'status AS status_code', 'status_details']
+    data_rows = query.select(cols).each_row.map do |po_cm_hash|
+      [
+        po_cm_hash['druid'], moab_storage_root_name(po_cm_hash['from_moab_storage_root_id']), storage_root.name,
+        po_cm_hash['last_checksum_validation'], po_cm_hash['last_moab_validation'], status_text_from_code(po_cm_hash['status_code']),
+        po_cm_hash['status_details']
+      ]
     end
-    detail_array
+    header_row + data_rows
+  end
+
+  def moab_storage_root_name(msr_id)
+    return nil unless msr_id.present?
+    @msr_names[msr_id] ||= MoabStorageRoot.find(msr_id).name
+  end
+
+  def status_text_from_code(status_code)
+    # statuses is a hash of the form { 'status_text' => status_code }.  this is just a reverse hash lookup.
+    CompleteMoab.statuses.to_a.find { |s| s[1] == status_code }[0]
   end
 
   # @param [Array] lines - values to output on each line of the csv