✨ Raise a more clear error when a type is not valid (#425)

Co-authored-by: Sebastián Ramírez <tiangolo@gmail.com>

sqlmodel/main.py

@@ -374,6 +374,7 @@ class SQLModelMetaclass(ModelMetaclass, DeclarativeMeta):
 
 
 def get_sqlalchemy_type(field: ModelField) -> Any:
+    if isinstance(field.type_, type) and field.shape == SHAPE_SINGLETON:
         if issubclass(field.type_, str):
             if field.field_info.max_length:
                 return AutoString(length=field.field_info.max_length)

tests/test_sqlalchemy_type_errors.py

@@ -0,0 +1,28 @@
+from typing import Any, Dict, List, Optional, Union
+
+import pytest
+from sqlmodel import Field, SQLModel
+
+
+def test_type_list_breaks() -> None:
+    with pytest.raises(ValueError):
+
+        class Hero(SQLModel, table=True):
+            id: Optional[int] = Field(default=None, primary_key=True)
+            tags: List[str]
+
+
+def test_type_dict_breaks() -> None:
+    with pytest.raises(ValueError):
+
+        class Hero(SQLModel, table=True):
+            id: Optional[int] = Field(default=None, primary_key=True)
+            tags: Dict[str, Any]
+
+
+def test_type_union_breaks() -> None:
+    with pytest.raises(ValueError):
+
+        class Hero(SQLModel, table=True):
+            id: Optional[int] = Field(default=None, primary_key=True)
+            tags: Union[int, str]