Azure Function Error: Microsoft.Azure.WebJobs.Host: Error indexing method 'Function1'. Cannot bind parameter 'document' to type IAsyncCollector`

Question

I'm new to Azure Function and in my first function I'm using CosmosDB. Under the hood, function is doing its job perfectly but when I open my function in portal I'm getting this error.

Function (LOANGILITY-AZFUNCTION/ProductDetailsFunc) Error: Microsoft.Azure.WebJobs.Host: Error indexing method 'ProductDetailsFunc'. Microsoft.Azure.WebJobs.Host: Cannot bind parameter 'document' to type IAsyncCollector`1. Make sure the parameter Type is supported by the binding. If you're using binding extensions (e.g. Azure Storage, ServiceBus, Timers, etc.) make sure you've called the registration method for the extension(s) in your startup code (e.g. builder.AddAzureStorage(), builder.AddServiceBus(), builder.AddTimers(), etc.).

My Function Header Prototype is

public static async Task<HttpResponseMessage> Run(
        [HttpTrigger(AuthorizationLevel.Anonymous, "get", "post", Route = null)]HttpRequestMessage req,
        [DocumentDB(
            databaseName: "OB",
            collectionName: "ProductDetails",
            ConnectionStringSetting = "DBConnection")]IAsyncCollector<dynamic> document,
        TraceWriter log)

Generated json from my code is

{
  "generatedBy": "Microsoft.NET.Sdk.Functions-1.0.13",
  "configurationSource": "attributes",
  "bindings": [
    {
      "type": "httpTrigger",
      "methods": [
        "get",
        "post"
      ],
      "authLevel": "anonymous",
      "name": "req"
    }
  ],
  "disabled": false,
  "scriptFile": "../bin/Loangility01.dll",
  "entryPoint": "Loangility01.ProductDetailsFunc.Run"
}

I also see some other SO questions and they are talking about builder.something in the code and I'm not working on .Net Core Azure Function, my target Project Framework is 4.6.1.

Is that you want to use Azure Cosmos DB as input or output binding? — Jim Xu
If so, please refer to docs.microsoft.com/en-us/azure/azure-functions/… — Jim Xu
Friend yes I'm working with cosmos db in my azure function and it is basically output binding and even I'm saving my data in cosmos db successfully. Only the issue is I'm facing this error in my portal. — Usama Shahid

Jim Xu Jim Xu · Accepted Answer · 2019-09-19T05:24:43

According to my test, we can directly deploy Function to Azure via visual studio. But we need to manually configure some settings in local.settings.json such as Cosmos Db connection string. The detailed steps are as below

Develop My Code:

 public static class Function2
    {
        [FunctionName("Function2")]
        public static async Task<HttpResponseMessage> Run([HttpTrigger(AuthorizationLevel.Function, "get", "post", Route = null)]HttpRequestMessage req, [DocumentDB(
                databaseName: "ToDoItems",
                collectionName: "Items",
                ConnectionStringSetting = "CosmosDBConnection")]IAsyncCollector<dynamic> toDoItemsOut, TraceWriter log)
        {
            log.Info("C# HTTP trigger function processed a request.");

            // parse query parameter
            string name = req.GetQueryNameValuePairs()
                .FirstOrDefault(q => string.Compare(q.Key, "name", true) == 0)
                .Value;

            if (name == null)
            {
                // Get request body
                dynamic data = await req.Content.ReadAsAsync<object>();
                name = data?.name;
            }
            HttpResponseMessage response ;



            if (name == null) {
                response = req.CreateResponse(HttpStatusCode.BadRequest, "Please pass a name on the query string or in the request body");

            }
            else {

                response= req.CreateResponse(HttpStatusCode.OK, "Hello " + name);
            }
            await toDoItemsOut.AddAsync(response.Content);
            return response;
        }
    }

Deploy to Azure
Configure application settings

Test

Update Regarding the issue, it may be that you do not add your cosmos db connection string into application settings. Please check if you have added.

Besides if you have added it, you still have the error. You check you logs to get the detailed error message.

Azure Function Error: Microsoft.Azure.WebJobs.Host: Error indexing method 'Function1'. Cannot bind parameter 'document' to type IAsyncCollector`

2 Answers