the max_length in string field is not working!

[chenzhony]

First Check

• I added a very descriptive title here.
• I used the GitHub search to find a similar question and didn't find it.
• I searched the SQLModel documentation, with the integrated search.
• I already searched in Google "How to X in SQLModel" and didn't find any information.
• 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.

Commit to Help

• I commit to help with one of those options 👆

Example Code

let's give a more detail example;

app.py

from sqlmodel import Session

from database import create_db_and_tables, engine
from models import Hero, Team


def create_heroes():
    with Session(engine) as session:
        team_z_force = Team(name="Z-Forcexixixisfds", headquarters="Sister Margaret's Bar")

        hero_deadpond = Hero(
            name="Deadpondasdfads", secret_name="Dive Wilson", team=team_z_force, age=50
        )
        session.add(hero_deadpond)
        session.commit()

        session.refresh(hero_deadpond)

        print("Created hero:", hero_deadpond)
        print("Hero's team:", hero_deadpond.team)


def main():
    create_db_and_tables()
    create_heroes()


if __name__ == "__main__":
    main()

models.py:::::

from typing import List, Optional

from sqlmodel import Field, Relationship, SQLModel


class Team(SQLModel, table=True):
    id: Optional[int] = Field(default=None, primary_key=True)
    name: str = Field(index=True, max_length=5)
    headquarters: str

    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, max_length=5, min_length=4)
    secret_name: str
    age: Optional[int] = Field(default=None, index=True, ge=0, le=1)

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

Description

my question:::
my question is that, the sql insert in app.py show has error, because name is more than max_length, age 50 is not less 1 and greater than 1 !!!!

please help

Operating System

macOS

Operating System Details

No response

SQLModel Version

0.0.16

Python Version

3.10.9

Additional Context

No response

[joachimhuet]

This is embarrassing indeed, what you could do is use a pure SQLModel model object and inherit it:

class BaseTeam(SQLModel):
    name: str = Field(index=True, max_length=5)
    headquarters: str

class Team(BaseTeam, table=True):
    id: Optional[int] = Field(default=None, primary_key=True)
    heroes: List["Hero"] = Relationship(back_populates="team")

class BaseHero(SQLModel):
    name: str = Field(index=True, max_length=5, min_length=4)
    secret_name: str
    age: Optional[int] = Field(default=None, index=True, ge=0, le=1)
    team: Optional[Team] = None

class Hero(BaseHero, table=True):
    id: Optional[int] = Field(default=None, primary_key=True)
    team_id: Optional[int] = Field(default=None, foreign_key="team.id")
    team: Optional[Team] = Relationship(back_populates="heroes")


sqlite_file_name = "database.db"
sqlite_url = f"sqlite:///{sqlite_file_name}"

engine = create_engine(sqlite_url)

SQLModel.metadata.create_all(engine)

with Session(engine) as session:
    team_z_force = TeamBase(name="Z-Forcexixixisfds", headquarters="Sister Margaret's Bar")
    team = Team.model_validate(team_z_force)
    session.add(team)
    session.commit()
    session.refresh(team)

    hero_deadpond = HeroBase(
        name="Deadpondasdfads", secret_name="Dive Wilson", team=team, age=50
    )
    hero = Hero(
        **hero_deadpond.model_dump(exclude={"team"}),
        team_id=hero_deadpond.team.id if hero_deadpond.team else None
    )
    session.add(hero)
    session.commit()
    session.refresh(hero)

    print("Created hero:", hero)
    print("Hero's team:", hero.team)

[chenzhony]

thanks for you response

I got error... shown below. May I ask what is your sqlmodel version???

---

InvalidRequestError Traceback (most recent call last)
Cell In[5], line 11
8 name: str = Field(index=True, max_length=5)
9 headquarters: str
---> 11 class Team(BaseTeam, table=True):
12 id: Optional[int] = Field(default=None, primary_key=True)
13 heroes: List["Hero"] = Relationship(back_populates="team")

File ~/anaconda3/lib/python3.10/site-packages/sqlmodel/main.py:549, in SQLModelMetaclass.init(cls, classname, bases, dict_, **kw)
545 setattr(cls, rel_name, rel_value) # Fix #315
546 # SQLAlchemy no longer uses dict_
547 # Ref: sqlalchemy/sqlalchemy@428ea01
548 # Tag: 1.4.36
--> 549 DeclarativeMeta.init(cls, classname, bases, dict_, **kw)
550 else:
551 ModelMetaclass.init(cls, classname, bases, dict_, **kw)

File ~/anaconda3/lib/python3.10/site-packages/sqlalchemy/orm/decl_api.py:196, in DeclarativeMeta.init(cls, classname, bases, dict_, **kw)
193 cls.sa_registry = reg
195 if not cls.dict.get("abstract", False):
--> 196 as_declarative(reg, cls, dict)
197 type.init(cls, classname, bases, dict)

File ~/anaconda3/lib/python3.10/site-packages/sqlalchemy/orm/decl_base.py:244, in as_declarative(registry, cls, dict)
...
469 )
470 table = metadata.tables[key]
471 if extend_existing:

InvalidRequestError: Table 'team' is already defined for this MetaData instance. Specify 'extend_existing=True' to redefine options and columns on an existing Table object.
Output is truncated. View as a scrollable element or open in a text editor. Adjust cell output settings...

[joachimhuet]

Ouch, this just means you have to reset and start again, a table can only be defined once per instance.

if you are working in a notebook for example and execute the code that defines Team you have to restart the notebook before re-executing that cell or you will get that error.

And you must be careful not to declare a table that share the same name 2 times in your code execution.

Example:
First execution:

Second execution:

[chenzhony]

it worked, Thank you very much!!!!!!!!

what is the reason for that, I am newcomer for sqlmodel and this kind of development, if you could drop me some hint or keyword, I could search online myself.

many thanks!!!!!

[joachimhuet]

For the error 'mytable' is already defined it's just a protection not allowing to erase a table once it's been defined it prevents you from misnaming a second table with the same name and removing the first. But you can bypass that security by passing extend_existing=True`

class MyTable(SQLModel, table=True):
    __table_args__ = {'extend_existing': True}  # allows to bypass that security
    ...

And for your first error with constraints not being applied to the table object it's designed like that even if many people complain about it. Check this thread #52 for alternatives fixing this.

If you want to see a bit more how I structure a simple sqlmodel project you can look at my example project made to explain something to someone: https://github.com/joachimhuet/sqlmodel-project-example