Unable to use original type hint by defining relationship

[Whitroom]

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• I already read and followed all the tutorial in the docs and didn't find an answer.
• I already checked if it is not related to SQLModel but to Pydantic.
• I already checked if it is not related to SQLModel but to SQLAlchemy.

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Example Code

from typing import Optional

from sqlmodel import Field, SQLModel, Relationship, create_engine, Session

class Team(SQLModel, table=True):
    id: Optional[int] = Field(default=None, primary_key=True)
    name: str = Field(index=True)
    headquarters: str

    # key sentence
    heroes: list["Hero"] = Relationship(back_populates='team')

class Hero(SQLModel, table=True):
    id: Optional[int] = Field(default=None, primary_key=True)
    name: str = Field(index=True)
    secret_name: str
    age: Optional[int] = Field(default=None, index=True)

    team_id: Optional[int] = Field(default=None, foreign_key=Team.id)

database_url = f'mysql+mysqlconnector://{user}:{password}@{host}/{database_name}'

engine = create_engine(database_url, encoding='utf8', echo=True)

if __name__ == '__main__':
    SQLModel.metadata.create_all(engine)

Description

I create Hero and Team models and try to use python original type hint, but while running it, it occurs exceptions...

Traceback (most recent call last):
File "pydantic\validators.py", line 709, in pydantic.validators.find_validators
TypeError: issubclass() arg 1 must be a class

Traceback (most recent call last):
File "C:\Users\10620\Desktop\Code\Python\sqlmodel\table_relationship.py", line 5, in
class Team(SQLModel, table=True):
File "C:\Users\10620\AppData\Local\Programs\Python\Python310\lib\site-packages\sqlmodel\main.py", line 342, in init
temp_field = ModelField.infer(
File "pydantic\fields.py", line 488, in pydantic.fields.ModelField.infer
File "pydantic\fields.py", line 419, in pydantic.fields.ModelField.init
File "pydantic\fields.py", line 534, in pydantic.fields.ModelField.prepare
File "pydantic\fields.py", line 728, in pydantic.fields.ModelField._type_analysis
File "pydantic\fields.py", line 778, in pydantic.fields.ModelField._create_sub_type
File "pydantic\fields.py", line 419, in pydantic.fields.ModelField.init
File "pydantic\fields.py", line 539, in pydantic.fields.ModelField.prepare
File "pydantic\fields.py", line 801, in pydantic.fields.ModelField.populate_validators
File "pydantic\validators.py", line 718, in find_validators
RuntimeError: error checking inheritance of 'Hero' (type: str)

The solution is adding List from typing and replacing it, but I don't know how to solve this bug...

link: https://sqlmodel.tiangolo.com/tutorial/relationship-attributes/define-relationships-attributes/

Operating System

Windows

Operating System Details

No response

SQLModel Version

0.0.6

Python Version

3.10.1

Additional Context

No response

[byrman]

I am not sure I understand your question correctly, but here list["Hero"] should indeed be List["Hero"]. From Python 3.9 onwards, generic list[Hero] should work as well, I think, but that requires your code to be rearranged, so that Hero is defined before Team.

[aleksul]

@Whitroom pls update to pydantic v1.9.1 - it should be fixed

[Shuntw6096]

I meet a similar problem,

class Base(SQLModel):
    pass
class Test:
    basemodel = Base # type alias at here, classVar[type[Base]] also didn't work
    __slots__ = 'filename', 'datamodel'
    def __init__(self, filename: str, datamodel: Optional[Base] = None, **kwargs):
        self.filename = filename
        if datamodel is not None:
            assert isinstance(datamodel, self.basemodel) # self.basemodel is Any at here, should be type[Base]
            self.datamodel = datamodel
        else:
            self.datamodel = self.basemodel(**kwargs) # self.basemodel is Any at here, should be type[Base]

If you remove inheritance of Base, typehint work perfectly.
My stupid solution is adding a classmethod to get instance of Base,

class Base(SQLModel, table=True):
    @classmethod
    def get_instance(cls, data: dict):
        return Base(**data)


class Test:
    basemodel = Base.get_instance
    __slots__ = 'filename', 'datamodel'
    def __init__(self, filename: str, datamodel: Optional[Base] = None, **kwargs):
        self.filename = filename
        if datamodel is not None:
            assert isinstance(datamodel, self.basemodel)
            self.datamodel = datamodel
        else:
            self.datamodel = self.basemodel(**kwargs)

Btw, filename is private attribute of Base at first, but idk how to init it.

[thribhu]

Many to one relationship using sqlmodel and sqlalchemy along with alembic

When initializing mapper Mapper[Category(category)], expression "relationship("Mapped[List['SubCategory']]")" seems to be using a generic class as the argument to relationship(); please state the generic argument using an annotation, e.g. "subcategories: Mapped[Mapped[List['SubCategory']']] = relationship()\

I am facing an issue with many to one relationship. Having followed the official documentation, I created my relationship attributes inside my table.
However, I receive an error from sqlalchemy like the above. My code is simple

from sqlmodel import SQLModel
from sqlmodel import Field
from sqlmodel import Relationship
from typing import Optional
from typing import List

class Category(SQLModel, table=True):
  id: int | None = Field(default=None, primary_key=True)
  name: str = Field(..., title="Category name")
  subcategories: List['SubCategory'] = Relationship(back_populates='category')
 
class SubCategory(SQLModel, table=True):
  id: int | None = Field(default=None, primary_key=True)
  name: str = Field(..., title="Sub category name")
  category_id: int | None = Field(default=None, foreign_key='category.id')
  category: 'Category' | None = Relationship(back_populates='subcategories')

[nicksonthc]

Some updates here: I tested the tutorial code with the sample provided and found that using from future import annotations might cause a mapper error. After removing the import, it worked.

class Team(SQLModel, table=True):
    id: int | None = Field(default=None, primary_key=True)
    name: str = Field(index=True)
    headquarters: str

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


class Hero(SQLModel, table=True):
    id: int | None = Field(default=None, primary_key=True)
    name: str = Field(index=True)
    secret_name: str
    age: int | None = Field(default=None, index=True)

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

Import annotations might cause the mapper error

If in my model file got import annotations, then i will get the mappers error, after i remove from __future__ import annotations
from __future__ import annotations

Error

Tutorial i refer to - https://sqlmodel.tiangolo.com/tutorial/relationship-attributes/define-relationships-attributes/#declare-relationship-attributes

Context & Environments

python 3.12
pydantic==2.9.2
SQLAlchemy==2.0.35
sqlmodel==0.0.22

[iloveitaly]

@nicksonthc I just ran into this same problem. Do you happen to know why that import causes this particular error?

[YuriiMotov]

The code from initial comment seems to work fine in current version (after changing foreign_key=Team.id to foreign_key="team.id"):

from typing import Optional

from sqlmodel import Field, Relationship, SQLModel, create_engine

class Team(SQLModel, table=True):
    id: Optional[int] = Field(default=None, primary_key=True)
    name: str = Field(index=True)
    headquarters: str

    # key sentence
    heroes: list["Hero"] = Relationship(back_populates='team')

class Hero(SQLModel, table=True):
    id: Optional[int] = Field(default=None, primary_key=True)
    name: str = Field(index=True)
    secret_name: str
    age: Optional[int] = Field(default=None, index=True)

    team_id: Optional[int] = Field(default=None, foreign_key="team.id")  # Changed Team.id to "team.id"

database_url = 'sqlite:///'

engine = create_engine(database_url, echo=True)

if __name__ == '__main__':
    SQLModel.metadata.create_all(engine)

And, the code example of @thribhu can be fixed by changing 'Category' | None to Union['Category', None]:

from typing import List, Union

from sqlmodel import Field, Relationship, SQLModel

class Category(SQLModel, table=True):
  id: int | None = Field(default=None, primary_key=True)
  name: str = Field(..., title="Category name")
  subcategories: List['SubCategory'] = Relationship(back_populates='category')
 
class SubCategory(SQLModel, table=True):
  id: int | None = Field(default=None, primary_key=True)
  name: str = Field(..., title="Sub category name")
  category_id: int | None = Field(default=None, foreign_key='category.id')
  category: Union['Category',  None] = Relationship(back_populates='subcategories')

@Whitroom, could you please check it? Do you think we can close this issue now?