Use temporary negative IDs for rows created in a draft Changeset

app/Tables/BaseNumerator.php

@@ -3,7 +3,9 @@
 
 namespace App\Tables;
 
-
+/**
+ * Sequential ID assigner
+ */
 abstract class BaseNumerator
 {
     /** @var int */
@@ -39,10 +41,18 @@ abstract class BaseNumerator
             throw new \OutOfBoundsException("Column numerator has run out of allocated GCID slots");
 
         $key = $this->getKey($this->next);
-        $this->next++;
+        $this->advance();
         return $key;
     }
 
+    /**
+     * Advance to the next ID
+     */
+    protected function advance()
+    {
+        $this->next++;
+    }
+
     /**
      * Convert numeric index to a key
      *