refactor required field in model fields into decorator

orm/fields.py

@@ -6,7 +6,6 @@ import orm
 from orm.exceptions import ModelDefinitionError, RelationshipInstanceError
 
 from pydantic import BaseModel, Json
-from pydantic.fields import ModelField
 
 import sqlalchemy
 
@@ -14,6 +13,27 @@ if TYPE_CHECKING:  # pragma no cover
     from orm.models import Model
 
 
+class RequiredParams:
+    def __init__(self, *args: str) -> None:
+        self._required = list(args)
+
+    def __call__(self, model_field_class: Type["BaseField"]) -> Type["BaseField"]:
+        old_init = model_field_class.__init__
+        model_field_class._old_init = old_init
+
+        def __init__(instance: "BaseField", *args: Any, **kwargs: Any) -> None:
+            super(instance.__class__, instance).__init__(*args, **kwargs)
+            for arg in self._required:
+                if arg not in kwargs:
+                    raise ModelDefinitionError(
+                        f"{instance.__class__.__name__} field requires parameter: {arg}"
+                    )
+                setattr(instance, arg, kwargs.pop(arg))
+
+        model_field_class.__init__ = __init__
+        return model_field_class
+
+
 class BaseField:
     __type__ = None
 
@@ -95,17 +115,10 @@ class BaseField:
         return value
 
 
+@RequiredParams("length")
 class String(BaseField):
     __type__ = str
 
-    def __init__(self, *args: Any, **kwargs: Any) -> None:
-        if "length" not in kwargs:
-            raise ModelDefinitionError(
-                "Param length is required for String model field."
-            )
-        self.length = kwargs.pop("length")
-        super().__init__(*args, **kwargs)
-
     def get_column_type(self) -> sqlalchemy.Column:
         return sqlalchemy.String(self.length)
 
@@ -173,18 +186,10 @@ class BigInteger(BaseField):
         return sqlalchemy.BigInteger()
 
 
+@RequiredParams("length", "precision")
 class Decimal(BaseField):
     __type__ = decimal.Decimal
 
-    def __init__(self, *args: Any, **kwargs: Any) -> None:
-        if "length" not in kwargs or "precision" not in kwargs:
-            raise ModelDefinitionError(
-                "Params length and precision are required for Decimal model field."
-            )
-        self.length = kwargs.pop("length")
-        self.precision = kwargs.pop("precision")
-        super().__init__(*args, **kwargs)
-
     def get_column_type(self) -> sqlalchemy.Column:
         return sqlalchemy.DECIMAL(self.length, self.precision)
 

orm/models.py

@@ -6,7 +6,6 @@ from typing import Any, List, Optional, TYPE_CHECKING, Tuple, Type, TypeVar
 from typing import Callable, Dict, Set
 
 import databases
-from pydantic.fields import ModelField
 
 import orm.queryset as qry
 from orm.exceptions import ModelDefinitionError
@@ -15,6 +14,7 @@ from orm.relations import RelationshipManager
 
 import pydantic
 from pydantic import BaseConfig, BaseModel, create_model
+from pydantic.fields import ModelField
 
 import sqlalchemy
 
@@ -42,10 +42,10 @@ def register_relation_on_build(table_name: str, field: ForeignKey, name: str) ->
     )
 
 
-def expand_reverse_relationships(model: Type["Model"]):
+def expand_reverse_relationships(model: Type["Model"]) -> None:
-    for field_name, model_field in model.__model_fields__.items():
+    for model_field in model.__model_fields__.values():
         if isinstance(model_field, ForeignKey):
-            child_model_name = model_field.related_name or model.__name__.lower() + 's'
+            child_model_name = model_field.related_name or model.__name__.lower() + "s"
             parent_model = model_field.to
             child = model
             if (