Middleware for Google NDB

I am trying to create a middleware for Google NDB. It requires the use of an context / the wrapping of the actual code within a “with” statement. It is recommended to create a single context for each HTTP Request. E.g.:

app = FastAPI()
client = ndb.Client()

class Contact(ndb.Model):
    name = ndb.StringProperty()
    phone = ndb.StringProperty()
    email = ndb.StringProperty()

@app.get("/create")
def create():
    with client.context():
        contact1 = Contact(name="John Smith",
                           phone="555 617 8993",
                           email="[e-mail]")
        contact1.put()

I tried to implement the “with-wrapping” within a middleware:

@app.middleware("http")
async def add_datastore(request: Request, call_next):
    with client.context():
        response = await call_next(request)
        return response

@app.get("/create_no_ctx")
def create_no_ctx():
    contact1 = Contact(name="John Smith",
                       phone="555 617 8993",
                       email="[e-mail]")
    contact1.put()

This middleware has no effect. Calling the create_no_ctx route yields a NDB-Exception that no context was set. Is is possible to create a middleware that wraps all route functions in a with statement with the context?

[ndavydovdev]

I created a pull request with the fix according to https://www.python.org/dev/peps/pep-0567/#converting-code-that-uses-threading-local It really works fine and I hope it will be merged

[phy25]

Opps this is a won’t fix on their end because of possible alternatives: https://github.com/googleapis/python-ndb/issues/289