Azure function written in python has 500 when “id” binding points doesn't have a corrseponding item in cosmosDB collection

Question

I have been experimenting with azure functions using python. I have followed the guide found at https://docs.microsoft.com/en-us/azure/azure-functions/functions-bindings-cosmosdb-v2#http-trigger-look-up-id-from-query-string-python. This works fine, I can query the enpoint using ?id=0 and I get the correct response. Although as soon as I replace the 0 with an id that is not present in my cosmos db in azure it throws a 500. The corresponding javascript example works.

Stack trace:

[9/17/19 5:53:18 PM] Executed 'Functions.HttpReader' (Failed, Id=23f0d832-5d00-4ffc-a5b9-3e20fed1c105)
[9/17/19 5:53:18 PM] System.Private.CoreLib: Exception while executing function: Functions.HttpReader. System.Private.CoreLib: Result: Failure
[9/17/19 5:53:18 PM] Exception: AttributeError: 'NoneType' object has no attribute 'type'
[9/17/19 5:53:18 PM] Stack:   File "/usr/local/Cellar/azure-functions-core-tools/2.7.1585/workers/python/deps/azure_functions_worker/dispatcher.py", line 294, in _handle__invocation_request
[9/17/19 5:53:18 PM]     pytype=pb_type_info.pytype)
[9/17/19 5:53:18 PM]   File "/usr/local/Cellar/azure-functions-core-tools/2.7.1585/workers/python/deps/azure_functions_worker/bindings/meta.py", line 63, in from_incoming_proto
[9/17/19 5:53:18 PM]     return binding.decode(datum, trigger_metadata=metadata)
[9/17/19 5:53:18 PM]   File "/usr/local/Cellar/azure-functions-core-tools/2.7.1585/workers/python/deps/azure/functions/cosmosdb.py", line 23, in decode
[9/17/19 5:53:18 PM]     data_type = data.type
[9/17/19 5:53:18 PM] .

Code:

import logging
import azure.functions as func


def main(req: func.HttpRequest, doc: func.DocumentList) -> func.HttpResponse:
    logging.warn('Python HTTP trigger function processed a request.')
    if not doc:
        return func.HttpResponse(
            "Not found",
            status_code=404
        )
    else:
        return func.HttpResponse(
            body=doc[0].to_json(),
            status_code=200
        )

function.json:

{
  "scriptFile": "__init__.py",
  "bindings": [
    {
      "authLevel": "function",
      "type": "httpTrigger",
      "direction": "in",
      "name": "req",
      "methods": [
        "get",
        "post"
      ]
    },
    {
      "type": "http",
      "direction": "out",
      "name": "$return"
    },
    {
      "type": "cosmosDB",
      "name": "doc",
      "databaseName": "<my-cosmos>",
      "collectionName": "<my-col>",
      "connectionStringSetting": "<conn-string>",
      "direction": "in",
      "id": "{Query.id}"
    }
  ]
}

To me this seems like a bug, but I am feel like I need a sanity check.

So is this a bug? Or have I messed something up?

I am querying it as shown above with ?id=0. I am unsure if this gets interpreted as a string or a number as it happens outside of my function. Did I understand your question correctly? @MatiasQuaranta — Gustav Eiman

jeffhollan jeffhollan · Accepted Answer · 2019-09-18T05:40:17

Yep. This looks like a bug in the Python library that does the conversion into a func.Document. I confirmed the below code works as expected in JavaScript:

module.exports = async function (context, req) {
    context.log('JavaScript HTTP trigger function processed a request.');

    if (context.bindings.document == null)
    {
        context.res = {
            statusCode: 400
        }
    }
    else
    {
        context.res = {
            statusCode: 200,
            body: context.bindings.document
        }
    }
};

Thanks for surfacing. Opened this issue to track

If wanting to do this pattern in Python currently you'd have to not use input bindings and fetch the document using the CosmosDB python SDK based on the query parameter.

Azure function written in python has 500 when “id” binding points doesn't have a corrseponding item in cosmosDB collection

1 Answers