feat: add Singleton metaclass

Author: NightMarcher

examples/service/scripts/demo.py

@@ -3,11 +3,17 @@
 """
 from asyncio import gather, run, sleep
 
-from fastapi_esql import timing
+from fastapi_esql import Singleton, timing
 
 from .. import app
 
 
+class Parent(metaclass=Singleton):pass
+
+
+class Child(Parent):pass
+
+
 async def work(sec):
     print(f"starting sleep {sec}")
     await sleep(sec)
@@ -21,6 +27,9 @@ async def main():
 
     await gather(work(1), work(2), work(3))
 
+    print(id(Parent()), id(Parent()))
+    print(id(Child()), id(Child()))
+
 
 if __name__ == "__main__":
     run(main())

fastapi_esql/__init__.py

@@ -14,6 +14,7 @@
     Cases,
     RawSQL,
     SQLizer,
+    Singleton,
     timing,
 )
 
@@ -29,6 +30,7 @@
     "Cases",
     "RawSQL",
     "SQLizer",
+    "Singleton",
     "timing",
 ]
 

fastapi_esql/utils/__init__.py

@@ -1,3 +1,4 @@
 from .cursor_handler import CursorHandler
 from .decorator import timing
+from .metaclass import Singleton
 from .sqlizer import Cases, RawSQL, SQLizer

fastapi_esql/utils/metaclass.py

@@ -0,0 +1,18 @@
+from abc import ABCMeta
+
+
+class Singleton(ABCMeta):
+    """
+    Singleton metaclass, using by:
+
+    >>> class Parent(BaseClass, metaclass=Singleton):pass
+    >>> class Child(Parent):pass
+    """
+    def __init__(self, *args, **kwargs):
+        self.__instance = None
+        super().__init__(*args, **kwargs)
+
+    def __call__(self, *args, **kwargs):
+        if not self.__instance:
+            self.__instance = super().__call__(*args, **kwargs)
+        return self.__instance

fastapi_esql/utils/sqlizer.py

@@ -9,7 +9,7 @@
 from ..const.error import QsParsingError, WrongParamsError
 
 logger = getLogger(__name__)
-# ensure the functionality of the RawSQL
+# To ensure the functionality of the RawSQL
 try:
     from tortoise.expressions import RawSQL
 except ImportError:
@@ -34,10 +34,10 @@ def __init__(self, field: str, whens: dict, default=None):
     @property
     def sql(self):
         whens = " ".join(
-            f"WHEN {k} THEN {SQLizer._sqlize_value(v)}"
+            f"WHEN {k} THEN {SQLizer.sqlize_value(v)}"
             for k, v in self.whens.items()
         )
-        else_ = " ELSE " + SQLizer._sqlize_value(self.default) if self.default is not None else ""
+        else_ = " ELSE " + SQLizer.sqlize_value(self.default) if self.default is not None else ""
         return f"CASE {self.field} {whens}{else_} END"
 
 
@@ -68,7 +68,7 @@ def resolve_wheres(
 
         modifier = QueryModifier()
         for q in qs:
-            # NOTE method `Q.resolve` changed since V0.18.0
+            # NOTE Method `Q.resolve` changed since version 0.18.0
             # https://github.com/tortoise/tortoise-orm/commit/37178e175bc12bc4767b93142dab0209f9240c55
             if __version__ >= "0.18.0":
                 modifier &= q.resolve(model, model._meta.basetable)
@@ -88,7 +88,7 @@ def resolve_orders(cls, orders: List[str]) -> str:
         return ", ".join(orders_)
 
     @classmethod
-    def _sqlize_value(cls, value, to_json=False) -> str:
+    def sqlize_value(cls, value, to_json=False) -> str:
         """
         Works like aiomysql.connection.Connection.escape
         """
@@ -169,12 +169,12 @@ def update_json_field(
             json_obj = f"JSON_REMOVE({json_obj}, {rps})"
         if path_value_dict:
             pvs = [
-                f"'{path}',{cls._sqlize_value(value, to_json=True)}"
+                f"'{path}',{cls.sqlize_value(value, to_json=True)}"
                 for (path, value) in path_value_dict.items()
             ]
             json_obj = f"JSON_SET({json_obj}, {', '.join(pvs)})"
         if merge_dict:
-            json_obj = f"JSON_MERGE_PATCH({json_obj}, {cls._sqlize_value(merge_dict)})"
+            json_obj = f"JSON_MERGE_PATCH({json_obj}, {cls.sqlize_value(merge_dict)})"
 
         sql = f"""
     UPDATE {table} SET {json_field} =
@@ -196,7 +196,7 @@ def upsert_on_duplicate(
             raise WrongParamsError("Please check your params")
 
         values = [
-            f"({', '.join(cls._sqlize_value(d.get(f)) for f in insert_fields)})"
+            f"({', '.join(cls.sqlize_value(d.get(f)) for f in insert_fields)})"
             for d in dicts
         ]
         # NOTE Beginning with MySQL 8.0.19, it is possible to use an alias for the row
@@ -236,7 +236,7 @@ def insert_into_select(
         assign_fields = []
         for k, v in assign_field_dict.items():
             fields.append(k)
-            assign_fields.append(f"{cls._sqlize_value(v)} {k}")
+            assign_fields.append(f"{cls.sqlize_value(v)} {k}")
 
         sql = f"""
     INSERT INTO {to_table or table}
@@ -259,14 +259,14 @@ def build_fly_table(
 
         if using_values:
             rows = [
-                f"ROW({', '.join(cls._sqlize_value(d.get(f)) for f in fields)})"
+                f"ROW({', '.join(cls.sqlize_value(d.get(f)) for f in fields)})"
                 for d in dicts
             ]
             values = "VALUES\n            " + ", ".join(rows)
             table = f"fly_table ({', '.join(fields)})"
         else:
             rows = [
-                f"SELECT {', '.join(f'{cls._sqlize_value(d.get(f))} {f}' for f in fields)}"
+                f"SELECT {', '.join(f'{cls.sqlize_value(d.get(f))} {f}' for f in fields)}"
                 for d in dicts
             ]
             values = " UNION ".join(rows)