Creating shared schema multi-tenancy using python

app.py

app = FastAPI(
        title="Project X",
        description="Project X API",
        version="1.0.0"
      ],
    )
app.include_router(v1_router, prefix="/api/v1", dependencies=[Depends(AppOrigin)])

middleware.apporigin.py

from fastapi import Request, Header, HTTPException
from core.db import session
from app.models import Tenant


class AppOrigin:
    def __init__(self, request: Request, app_origin: int = Header(None)):

        if not app_origin:
            raise HTTPException(status_code=422, detail="App-Origin header invalid")

        tenant = session.query(Tenant).filter(Team.id==app_origin).first()
        request.tenant = tenant
        session.info['tenant'] = tenant
        

models.user.py

from sqlalchemy import Column, Unicode, BigInteger, Boolean

from core.db import Base
from core.db.mixins import TenantMixin


class User(Base, TenantMixin):
    __tablename__ = "users"
    __multitenant__ = True

    id = Column(BigInteger, primary_key=True, autoincrement=True)
    password = Column(Unicode(255), nullable=False)
    email = Column(Unicode(255), nullable=False, unique=True)
    name = Column(Unicode(255))

tenant_mixin.py

from sqlalchemy import Column, inspect, BigInteger, func, event
from sqlalchemy.ext.declarative import declared_attr
from sqlalchemy.orm import Query

from core.db import session

class TenantMixin:

    @declared_attr
    def tenant_id(cls):
        if not cls.__multitenant__:
            return None
        
        return Column(BigInteger, nullable=False, default=_current_session_tenant)

def _current_session_tenant():
    try:
        tenant = session.info.get('tenant', False)
        if not tenant:
            return 1
        
        return tenant.id
    except:
        return 1


@event.listens_for(Query, 'before_compile', retval=True)
def before_compile(query):
    tenant_safe = query._execution_options.get('tenant_safe', False)
    if tenant_safe:
        return query
    
    for column in query.column_descriptions:
        entity = column['entity']
        if entity is None:
            continue

        inspector = inspect(column['entity'])
        mapper = getattr(inspector, 'mapper', None)
        if mapper and issubclass(mapper.class_, TenantMixin):
            query = query.enable_assertions(False).filter(
                entity.tenant_id.__eq__(query.session.info.get('tenant').id),
            )

    return query

usecase.py

userById = session.query(User).filter(User.id == user_id).first()