🐛 Fix TypeError for fields annotated with Literal

sqlmodel/_compat.py

@@ -10,6 +10,7 @@
     Dict,
     ForwardRef,
     Generator,
+    Literal,
     Mapping,
     Optional,
     Set,
@@ -23,6 +24,8 @@
 from pydantic.fields import FieldInfo
 from typing_extensions import Annotated, get_args, get_origin
 
+from .sql.sqltypes import AutoString
+
 # Reassign variable to make it reexported for mypy
 PYDANTIC_VERSION = P_VERSION
 PYDANTIC_MINOR_VERSION = tuple(int(i) for i in P_VERSION.split(".")[:2])
@@ -459,7 +462,9 @@ def is_field_noneable(field: "FieldInfo") -> bool:
         return field.allow_none  # type: ignore[no-any-return, attr-defined]
 
     def get_sa_type_from_field(field: Any) -> Any:
-        if isinstance(field.type_, type) and field.shape == SHAPE_SINGLETON:
+        if get_origin(field.type_) is Literal:
+            return AutoString
+        elif isinstance(field.type_, type) and field.shape == SHAPE_SINGLETON:
             return field.type_
         raise ValueError(f"The field {field.name} has no matching SQLAlchemy type")
 

sqlmodel/main.py

@@ -655,6 +655,9 @@ def get_sqlalchemy_type(field: Any) -> Any:
     type_ = get_sa_type_from_field(field)
     metadata = get_field_metadata(field)
 
+    # Checks for `Literal` type annotation
+    if type_ is Literal:
+        return AutoString
     # Check enums first as an enum can also be a str, needed by Pydantic/FastAPI
     if issubclass(type_, Enum):
         return sa_Enum(type_)

tests/test_main.py

@@ -1,4 +1,4 @@
-from typing import List, Optional
+from typing import List, Literal, Optional
 
 import pytest
 from sqlalchemy.exc import IntegrityError
@@ -125,3 +125,25 @@ class Hero(SQLModel, table=True):
         # The next statement should not raise an AttributeError
         assert hero_rusty_man.team
         assert hero_rusty_man.team.name == "Preventers"
+
+
+def test_literal_typehints_are_treated_as_strings(clear_sqlmodel):
+    """Test https://github.com/fastapi/sqlmodel/issues/57"""
+
+    class Hero(SQLModel, table=True):
+        id: Optional[int] = Field(default=None, primary_key=True)
+        name: str = Field(unique=True)
+        weakness: Literal["Kryptonite", "Dehydration", "Munchies"]
+
+    superguy = Hero(name="Superguy", weakness="Kryptonite")
+
+    engine = create_engine("sqlite://", echo=True)
+
+    SQLModel.metadata.create_all(engine)
+
+    with Session(engine) as session:
+        session.add(superguy)
+        session.commit()
+        session.refresh(superguy)
+        assert superguy.weakness == "Kryptonite"
+        assert isinstance(superguy.weakness, str)