--- /dev/null
+<?php
+
+namespace Drupal\workspaces\Plugin\Validation\Constraint;
+
+use Symfony\Component\Validator\Constraint;
+
+/**
+ * Deleted workspace constraint.
+ *
+ * @Constraint(
+ * id = "DeletedWorkspace",
+ * label = @Translation("Deleted workspace", context = "Validation"),
+ * )
+ */
+class DeletedWorkspaceConstraint extends Constraint {
+
+ /**
+ * The default violation message.
+ *
+ * @var string
+ */
+ public $message = 'A workspace with this ID has been deleted but data still exists for it.';
+
+}