✨ Use mysql's default string length for mariadb

[itsbekas]

As I presented in #881 , mariadb doesn't have a default string size, unlike mysql, which leads to an sqlalchemy compile error. From what I understood (and tried), simply using the mysql default length and checking for the mariadb dialect.name is enough to prevent this error.

[itsbekas]

I realize now that it might be worth mentioning that the reason I wanted the default value was because setting the max_length metadata wasn't working. After some digging I ended up finding this pull request: #857 which fixes that part of the problem, so maybe these 2 could be merged as they fix different ends of the same problem.

[stevleibelt]

Damn, so I just ran into this issue when I've executed alembic upgrade head so far.

This is really sad since - if I get it right - this will stop me from using sqlmodel in my current project and switch back to sqlalchemy :(.

Thanks for your PR.

[jaspermohl]

Any estimation when this will be merged?
Running also into the issues with MariaDB and the changes make it work for me as well.

[YuriiMotov]

LGTM

I attempted to add a test, but failed to make it working.
The idea was to create DDL without real connection using ddl = str(CreateTable(Hero.__table__).compile(engine, dialect=dialect)), but in this case dialect is always mysql.
I tried setting dialect.server_version_info = (10, 6, 0) with no effect.

Tested it locally with real connection and it works.

How to test locally

docker-compose.yaml

version: "3"

services:

  mariadb:
    image: "mariadb:10.6"
    restart: 'always'
    ports:
      - "3306:3306"
    environment:
      MYSQL_ROOT_PASSWORD: "mysecretpassword"
      MYSQL_DATABASE: "some_db"
      MYSQL_USER: "user"
      MYSQL_PASSWORD: "mysecretpassword"

test.py

from sqlmodel import SQLModel, create_engine, Field


class Hero(SQLModel, table=True):
    name: str = Field(primary_key=True)


database_url = "mariadb+mariadbconnector://user:mysecretpassword@127.0.0.1:3306/some_db"
engine = create_engine(database_url, echo=True)

SQLModel.metadata.drop_all(engine)
SQLModel.metadata.create_all(engine)

Before applying changes it fails with sqlalchemy.exc.CompileError: (in table 'hero', column 'name'): VARCHAR requires a length on dialect mariadb, after - works:

CREATE TABLE hero (
        name VARCHAR(255) NOT NULL, 
        PRIMARY KEY (name)
)