diff --git a/bookshop/server.js b/bookshop/server.js
index 46467b15..35c74e15 100644
--- a/bookshop/server.js
+++ b/bookshop/server.js
@@ -1,21 +1,28 @@
 //
 //  Quick and dirty implementation for cds.validate() using db-level constraints
+//  Test in cds.repl like that:
+//  await cds.run (()=> INSERT.into (Books, { title:'   ', author_ID:150 }) .then (cds.validate(Books)))
 //
 
 const cds = require('@sap/cds')
 cds.on('served', ()=> {
 
-  const $ = cds.validate; cds.validate = async function (entity, key, ...columns) {
+  const $ = cds.validate; cds.validate = function (entity, key, ...columns) {
+
     if (!entity.is_entity) return $(...arguments)
+    if (!key) return key => cds.validate(entity,key)
+
     if (entity.constraints) entity = entity.constraints
-    if (key?.results) key = key.results[0].lastInsertRowid
-    const checks = await SELECT.one.from (entity, key, columns.length && columns)
-    const failed = {}; for (let c in checks) {
-      if (c in entity.keys) continue
-      if (c[0] == '_') continue
-      if (checks[c]) failed[c] = checks[c]
-    }
-    if (Object.keys(failed).length) throw cds.error `Invalid input: ${failed}`
+    if (key.results) key = key.results[0].lastInsertRowid
+
+    return SELECT.one.from (entity, key, columns.length && columns) .then (checks => {
+      const failed = {}; for (let c in checks) {
+        if (c in entity.keys) continue
+        if (c[0] == '_') continue
+        if (checks[c]) failed[c] = checks[c]
+      }
+      if (Object.keys(failed).length) throw cds.error `Invalid input: ${failed}`
+    })
   }
 
 })