Revert "Optimise inserting derivation inputs"

I'm concerned that this approach is more error prone and won't error if there
are issues with the data in the database.

This reverts commit 3081887b90.

guix-data-service/model/derivation.scm

@@ -1105,6 +1105,25 @@ ON CONFLICT DO NOTHING"
                 (vector->list (json-string->scm env_vars)))
            system))))
 
+(define select-derivation-output-id
+  (mlambda (conn name path)
+    (match (exec-query
+            conn
+            "
+SELECT derivation_outputs.id FROM derivation_outputs
+INNER JOIN derivations
+  ON derivation_outputs.derivation_id = derivations.id
+WHERE derivations.file_name = $1
+  AND derivation_outputs.name = $2"
+            (list path
+                  name))
+      (((id))
+       id)
+      (()
+       (error (simple-format
+               #f "cannot find derivation-output with name ~A and path ~A"
+               name path))))))
+
 (define (select-derivation-outputs-by-derivation-id conn id)
   (define query
     (string-append
@@ -1377,9 +1396,23 @@ WHERE derivation_source_files.store_path = $1"
         #f)))
 
 (define (insert-derivation-inputs conn derivation-ids derivations)
-  (let ((query-parts
-         (append-map!
-          (lambda (derivation-id derivation)
+  (define (insert-into-derivation-inputs derivation-id output-ids)
+    (for-each
+     (lambda (output-id)
+       (exec-query
+        conn
+        "
+INSERT INTO derivation_inputs (derivation_id, derivation_output_id)
+VALUES ($1, $2);"
+        (list (number->string derivation-id) output-id)))
+     output-ids))
+
+  (vector-for-each
+   (lambda (i derivation-id derivation)
+     (let ((inputs (derivation-inputs derivation)))
+       (unless (null? inputs)
+         (insert-into-derivation-inputs
+          derivation-id
           (append-map!
            (match-lambda
              (($ <derivation-input> derivation-or-path sub-derivations)
@@ -1392,34 +1425,13 @@ WHERE derivation_source_files.store_path = $1"
                        ((? string? s)
                         s))))
                 (map (lambda (sub-derivation)
-                         (string-append "("
-                                        (number->string derivation-id)
-                                        ", '" path
-                                        "', '" sub-derivation "')"))
+                       (select-derivation-output-id conn
+                                                    sub-derivation
+                                                    path))
                      sub-derivations))))
-             (derivation-inputs derivation)))
-          (vector->list derivation-ids)
-          (vector->list derivations))))
-
-    (chunk-for-each!
-     (lambda (query-parts-chunk)
-       (exec-query
-        conn
-        (string-append
-         "
-INSERT INTO derivation_inputs (derivation_id, derivation_output_id)
-SELECT vals.derivation_id, derivation_outputs.id
-FROM (VALUES "
-         (string-join query-parts-chunk ", ")
-         ") AS vals (derivation_id, file_name, output_name)
-INNER JOIN derivations
-  ON derivations.file_name = vals.file_name
-INNER JOIN derivation_outputs
-  ON derivation_outputs.derivation_id = derivations.id
- AND vals.output_name = derivation_outputs.name
-ON CONFLICT DO NOTHING")))
-     1000
-     query-parts)))
+           inputs)))))
+   derivation-ids
+   derivations))
 
 (define (insert-derivation-sources conn derivation-id sources)
   (define (insert-into-derivation-sources derivation-source-file-ids)