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

datalite/commons.py

@@ -1,8 +1,14 @@
 from dataclasses import Field
 from typing import Any, Optional, Dict, List
+from .constraints import Unique
 import sqlite3 as sql
 
 
+type_table: Dict[Optional[type], str] = {None: "NULL", int: "INTEGER", float: "REAL",
+                                         str: "TEXT", bytes: "BLOB"}
+type_table.update({Unique[key]: f"{value} NOT NULL UNIQUE" for key, value in type_table.items()})
+
+
 def _convert_type(type_: Optional[type], type_overload: Dict[Optional[type], str]) -> str:
     """
     Given a Python type, return the str name of its
@@ -30,7 +36,9 @@ def _convert_sql_format(value: Any) -> str:
     >>> _convert_sql_format("John Smith")
     '"John Smith"'
     """
-    if isinstance(value, str):
+    if value is None:
+        return "NULL"
+    elif isinstance(value, str):
         return f'"{value}"'
     elif isinstance(value, bytes):
         return '"' + str(value).replace("b'", "")[:-1] + '"'
@@ -82,5 +90,5 @@ def _create_table(class_: type, cursor: sql.Cursor, type_overload: Dict[Optional
     sql_fields = "obj_id INTEGER PRIMARY KEY AUTOINCREMENT, " + sql_fields
     cursor.execute(f"CREATE TABLE IF NOT EXISTS {class_.__name__.lower()} ({sql_fields});")
 
-type_table: Dict[Optional[type], str] = {None: "NULL", int: "INTEGER", float: "REAL",
-                                                 str: "TEXT", bytes: "BLOB"}
+
+

datalite/constraints.py

@@ -0,0 +1,26 @@
+"""
+datalite.constraints module introduces constraint
+    types that can be used to hint field variables,
+    that can be used to signal datalite decorator
+    constraints in the database.
+"""
+from typing import TypeVar, Union, Tuple
+
+T = TypeVar('T')
+
+
+class ConstraintFailedError(Exception):
+    """
+    This exception is raised when a Constraint fails.
+    """
+    pass
+
+
+"""
+Dataclass fields hinted with this type signals
+    datalite that the bound column of this
+    field in the table is NOT NULL and UNIQUE.
+"""
+Unique = Union[Tuple[T], T]
+
+

datalite/datalite_decorator.py

@@ -2,10 +2,12 @@
 Defines the Datalite decorator that can be used to convert a dataclass to
 a class bound to a sqlite3 database.
 """
-
+from sqlite3.dbapi2 import IntegrityError
 from typing import Dict, Optional, List, Callable
 from dataclasses import Field, asdict
 import sqlite3 as sql
+
+from constraints import ConstraintFailedError
 from .commons import _convert_sql_format, _convert_type, _create_table, type_table
 
 
@@ -22,11 +24,14 @@ def _create_entry(self) -> None:
         table_name: str = self.__class__.__name__.lower()
         kv_pairs = [item for item in asdict(self).items()]
         kv_pairs.sort(key=lambda item: item[0])  # Sort by the name of the fields.
-        cur.execute(f"INSERT INTO {table_name}("
-                    f"{', '.join(item[0] for item in kv_pairs)})"
-                    f" VALUES ({', '.join(_convert_sql_format(item[1]) for item in kv_pairs)});")
-        self.__setattr__("obj_id", cur.lastrowid)
-        con.commit()
+        try:
+            cur.execute(f"INSERT INTO {table_name}("
+                        f"{', '.join(item[0] for item in kv_pairs)})"
+                        f" VALUES ({', '.join(_convert_sql_format(item[1]) for item in kv_pairs)});")
+            self.__setattr__("obj_id", cur.lastrowid)
+            con.commit()
+        except IntegrityError:
+            raise ConstraintFailedError("A constraint has failed.")
 
 
 def _update_entry(self) -> None: