modules/entry/back/models/entry.js

@@ -46,4 +46,15 @@ module.exports = Self => {
             }
         }
     });
+
+    Self.observe('before delete', async function(ctx) {
+        let isBooked = ctx.instance && ctx.instance.isBooked;
+
+        if (isBooked === undefined) {
+            const entryInstance = await Self.findById(ctx.where.id);
+            isBooked = entryInstance.isBooked;
+        }
+
+        if (isBooked) throw new Error('Booked entry cannot be deleted');
+    });
 };