ValueError: <class 'list'> has no matching SQLAlchemy type

[fabiobeoni]

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Example Code

# hero.py (works)
class Hero(SQLModel, table=True):
    id: int | None = Field(default=None, primary_key=True)
    ....

    team_id: int | None = Field(default=None, foreign_key="team.id")
    team: Team | None = Relationship(back_populates="heroes")


# team.py (works)
class Team(SQLModel, table=True):
    id: int | None = Field(default=None, primary_key=True)
    .....

    heroes: list["Hero"] = Relationship(back_populates="team")


# todo.py (does not work)
class Todo(SQLModel, table=True):

    id: UUID | None = Field(
        default=uuid4(),
        primary_key=True,
    )

    ......

    category_id: UUID | None = Field(default=None, foreign_key="category.id")
    category: Category | None  = Relationship(back_populates="todos")


# category.py  (does not work => ValueError: <class 'list'>)
class Category(SQLModel, table=True):
    id: UUID | None = Field(default=uuid4(), primary_key=True)
    .....

    todos: list["Todo"] = Relationship(back_populates="category")

Description

Given these classes and 1-to-N relationships, I get compile time error: ValueError: <class 'list'> has no matching SQLAlchemy type referring to the category.py field todos: list["Todo"], while the relation hero/team does work.

I cannot see any relevant difference between todo/category implementation and hero/team implementation to justify the error:

import todo.models.category
  File ".../todo/models/category.py", line 9, in <module>
    class Category(SQLModel, table=True):
  File ".../lib/python3.12/site-packages/sqlmodel/main.py", line 559, in __new__
    col = get_column_from_field(v)
          ^^^^^^^^^^^^^^^^^^^^^^^^
  File "../lib/python3.12/site-packages/sqlmodel/main.py", line 708, in get_column_from_field
    sa_type = get_sqlalchemy_type(field)
              ^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "../lib/python3.12/site-packages/sqlmodel/main.py", line 697, in get_sqlalchemy_type
    raise ValueError(f"{type_} has no matching SQLAlchemy type")
ValueError: <class 'list'> has no matching SQLAlchemy type

Operating System

Linux

Operating System Details

fastapi 0.115.6 FastAPI framework, high performance, easy to learn, fast to code, ready for production
├── pydantic >=1.7.4,<1.8 || >1.8,<1.8.1 || >1.8.1,<2.0.0 || >2.0.0,<2.0.1 || >2.0.1,<2.1.0 || >2.1.0,<3.0.0
│ ├── annotated-types >=0.6.0
│ ├── pydantic-core 2.27.2
│ │ └── typing-extensions >=4.6.0,<4.7.0 || >4.7.0
│ └── typing-extensions >=4.12.2 (circular dependency aborted here)
├── starlette >=0.40.0,<0.42.0
│ └── anyio >=3.4.0,<5
│ ├── idna >=2.8
│ ├── sniffio >=1.1
│ └── typing-extensions >=4.5
└── typing-extensions >=4.8.0
python-dotenv 1.0.1 Read key-value pairs from a .env file and set them as environment variables
sqlmodel 0.0.22 SQLModel, SQL databases in Python, designed for simplicity, compatibility, and robustness.
├── pydantic >=1.10.13,<3.0.0
│ ├── annotated-types >=0.6.0
│ ├── pydantic-core 2.27.2
│ │ └── typing-extensions >=4.6.0,<4.7.0 || >4.7.0
│ └── typing-extensions >=4.12.2 (circular dependency aborted here)
└── sqlalchemy >=2.0.14,<2.1.0
├── greenlet !=0.4.17
└── typing-extensions >=4.6.0

SQLModel Version

0.0.22

Python Version

3.12

Additional Context

No response