Query for outputs when build events arrive

This will keep the substitute information more up to date.

guix-data-service/model/build.scm

@@ -26,6 +26,7 @@
   #:use-module (guix-data-service model derivation)
   #:use-module (guix-data-service model system)
   #:export (select-build-stats
+            select-build-outputs
             select-builds-with-context
             select-builds-with-context-by-derivation-file-name
             select-builds-with-context-by-derivation-output
@@ -121,6 +122,40 @@ ORDER BY status"))
                            ((sql . value) value))
                          (filter pair? criteria))))))
 
+(define (select-build-outputs conn build-id)
+  (match (exec-query
+          conn
+          "
+SELECT derivation_file_name, derivation_output_details_set_id
+FROM builds
+WHERE builds.id = $1"
+          (list (number->string build-id)))
+    (((derivation-file-name output-details-set-id))
+
+     (if output-details-set-id
+         (exec-query
+          conn
+          "
+SELECT derivation_output_details.path
+FROM derivation_output_details
+INNER JOIN derivation_output_details_sets
+  ON ARRAY[derivation_output_details.id] &&
+       derivation_output_details_sets.derivation_output_details_ids
+WHERE derivation_output_details_sets.id = $1"
+          (list output-details-set-id))
+         (exec-query
+          conn
+          "
+SELECT derivation_output_details.path
+FROM derivations
+INNER JOIN derivation_outputs
+  ON derivations.id = derivation_outputs.derivation_id
+INNER JOIN derivation_output_details
+  ON derivation_outputs.derivation_output_details_id
+      = derivation_output_details.id
+WHERE derivations.file_name = $1"
+          (list derivation-file-name))))))
+
 (define* (select-builds-with-context conn build-statuses build-server-ids
                                      #:key revision-commit
                                      system target