Unexpected model create behaviour for non-integer primary keys

When primary key is i.e. String, model instance returned from model.object.create has primary key as sequential integer. Once instance is fetched again, primary key is as expected - type and value wise. Postgres behaviour is similar. Returned instance primary key in this case is actually None. Same for UUID type. Once fetched again, everything is as expected.

Could be that problem originates from databases library or incorrect usage of it.

Two copy/paste tests.

import random

import databases
import pytest
import sqlalchemy

import orm
from tests.settings import DATABASE_URL
from tests.test_columns import async_adapter

database = databases.Database(DATABASE_URL, force_rollback=True)
metadata = sqlalchemy.MetaData()


def key():
    return "".join(random.choice("abcdefgh123456") for _ in range(8))


class Model(orm.Model):
    __tablename__ = "model"
    __metadata__ = metadata
    __database__ = database

    id = orm.String(primary_key=True, default=key, max_length=8)
    name = orm.String(max_length=32)


@pytest.fixture(autouse=True, scope="function")
def create_test_database():
    engine = sqlalchemy.create_engine(DATABASE_URL)
    metadata.create_all(engine)
    yield
    metadata.drop_all(engine)


@async_adapter
async def test_pk_1():
    model = await Model.objects.create(name="NAME")
    assert isinstance(model.id, str)


@async_adapter
async def test_pk_2():
    model = await Model.objects.create(name="NAME")
    assert await Model.objects.all() == [model]

[tomchristie]

@Nipsuli That’s really helpful thanks - we probably ought to update the create method along those lines.

[aminalaee]

@tomchristie @Nipsuli The proposed solution will work in PostgreSQL but not in MySQL and SQLite. SQLite does not support RETURNING clauses until version 3.35.0 and that is not still supported on current python versions.

For anyone interested, the reason this is happening is that SQLite uses a virtual column ROWID, after an INSERT is done, the driver will call last_insert_rowid() which returns an Integer ROWID. This can be solved by using the RETURNING clause but that’s not available yet.

As far as I know MySQL doesn’t support that either.

Any feedback is appreciated.