Merge branch '6.0' into 6

en/02_Developer_Guides/00_Model/12_Indexes.md

@@ -61,6 +61,11 @@ support the following:
 - `unique`: Index plus uniqueness constraint on the value
 - `fulltext`: Fulltext content index
 
+> [!NOTE]
+> Violating a unique index will throw a [`DuplicateEntryException`](api:SilverStripe\ORM\Connect\DuplicateEntryException) exception which you can catch and handle to produce appropriate validation messages.
+>
+> If the violation happens when calling [`DataObject::write()`](api:SilverStripe\ORM\DataObject::write()), the exception will be caught and a [`ValidationException`](api:SilverStripe\ORM\ValidationException) will be thrown instead. The CMS catches any `ValidationException` and displays them as user friendly validation errors in edit forms.
+
 ```php
 // app/src/MyTestObject.php
 namespace App\Model;