"When I inherit an ORM model that contains fields of type list or dict, I encounter the error <class 'list'> has no matching SQLAlchemy type. Why does this happen?"

[GJCoke]

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Example Code

from sqlmodel import SQLModel, Field, JSON, Column
from typing import List


class BaseItem(SQLModel, table=True):
    id: int = Field(default=None, primary_key=True)
    methods: List[str] = Field([], sa_column=Column(JSON))


class DerivedItem(BaseItem):
    pass

Description

Traceback (most recent call last):
File "/home/coke/.config/JetBrains/PyCharm2024.3/scratches/test.py", line 8, in
class DerivedItem(BaseItem):
File "/home/coke/PythonProject/Async-FastAPI-MultiDB/.venv/lib/python3.12/site-packages/sqlmodel/main.py", line 562, in new
col = get_column_from_field(v)
^^^^^^^^^^^^^^^^^^^^^^^^
File "/home/coke/PythonProject/Async-FastAPI-MultiDB/.venv/lib/python3.12/site-packages/sqlmodel/main.py", line 711, in get_column_from_field
sa_type = get_sqlalchemy_type(field)
^^^^^^^^^^^^^^^^^^^^^^^^^^
File "/home/coke/PythonProject/Async-FastAPI-MultiDB/.venv/lib/python3.12/site-packages/sqlmodel/main.py", line 700, 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

No response

SQLModel Version

0.0.24

Python Version

3.12

Additional Context

No response

[janas-adam]

hi @GJCoke,
try with:

methods: list[str] = Field(default_factory=list, sa_column=Column(JSON))

[GJCoke]

I’ve tried this approach, but it also has issues.

[janas-adam]

@GJCoke tried ur case with generating migrations

use table true in end-models and also sa_column can be tricky to inherit multiple times so sa_type is the solution:

class BaseItem(SQLModel):
    id: int = Field(default=None, primary_key=True)
    methods: List[str] = Field(default_factory=list, sa_type=JSON)

class DerivedItem1(BaseItem, table=True):
    pass
    
class DerivedItem2(BaseItem, table=True):
    pass

all went fine
migration for sa_type and sa_column is the same

hope it helped

[GJCoke]

Thank you very much.