Add unique constraint, None option

datalite/__init__.py

@@ -1,3 +1,12 @@
-__all__ = ['commons', 'datalite_decorator', 'fetch', 'migrations', 'datalite']
+__all__ = ['commons', 'datalite_decorator', 'fetch', 'migrations', 'datalite', 'constraints']
+
+from dataclasses import dataclass
+
 
 from .datalite_decorator import datalite
+
+
+@dataclass
+class Student:
+    id_: int
+    name: str