Question: I'm trying to build an Azure function in C# that creates a new document object in Azure cosmos DB using SQL API if an id doesn't already exist and updates a document object if it already exists.

The context behind this is logging chatbot conversation history to unique user sessions.

Input:

HTTP GET Request with parameters (id (string), chatHistory(string) and chatDateTime(string))

Output:

If document object with same id already exists - then update document with input chatHisotry and chatDateTime.

If no document object exists with same id then create a new document object with id, chatHistory and chatDateTime equal to input.

Any help much appreciated! Been struggling with this one for days.

Example of document object:

```
{
    "id": "ESCRfAKwlTbH8W5aVRLxgA",
    "chatHistory": "Hi, Hello",
    "chatDateTime": "Fri Sep 21 2018 05:34:35 GMT+0000 (Coordinated Universal Time)",
    "_rid": "RwYSAIqaSVg2AAAAAAAAAA==",
    "_self": "dbs/RwYSAA==/colls/RwYSAIqaSVg=/docs/RwYSAIqaSVg2AAAAAAAAAA==/",
    "_etag": "\"00007400-0000-0000-0000-5ba482ed0000\"",
    "_attachments": "attachments/",
    "_ts": 1537508077
}

```

Answer: 
You can use the Azure Functions' [Cosmos DB Output Binding](https://learn.microsoft.com/en-us/azure/azure-functions/functions-bindings-cosmosdb#output---examples). The Output binding does an **Upsert** operation.

```
[FunctionName("HttpTriggerWithSingleDocument")]
    public static async Task<HttpResponseMessage> Run(
        [HttpTrigger(AuthorizationLevel.Function, "get", "post", Route = null)]HttpRequestMessage req,
        [DocumentDB(databaseName: "your-db",
            collectionName: "your-collection",
            ConnectionStringSetting = "CosmosDBConnectionString")] out dynamic documentToSave)
    {
        dynamic data = await req.Content.ReadAsAsync<object>();

        if (data == null)
        {
            documentToSave = null;
            return req.CreateResponse(HttpStatusCode.BadRequest);
        }

        documentToSave = data;

        return req.CreateResponse(HttpStatusCode.Created);
}

```

Azure Portal version:

```
using System.Net;

public static async Task<HttpResponseMessage> Run(
            HttpRequestMessage req,
            IAsyncCollector<dynamic> documentsToStore)
        {
            dynamic data = await req.Content.ReadAsAsync<object>();

            if (data == null)
            {
                return req.CreateResponse(HttpStatusCode.BadRequest);
            }

            await documentsToStore.AddAsync(data);

            return req.CreateResponse(HttpStatusCode.Created);
    }

```

And you also need the `function.json` updated to something like: 

```
{
  "bindings": [
    {
      "name": "req",
      "type": "httpTrigger",
      "direction": "in"
    },
    {
      "name": "$return",
      "type": "http",
      "direction": "out"
    },
    {
      "type": "documentDB",
      "name": "documentsToStore",
      "databaseName": "<your-database-name>",
      "collectionName": "<your-collection-name>",
      "createIfNotExists": false,
      "connection": "<your-connection-setting-name>",
      "direction": "out"
    }
  ]
}

```

More samples available here: <https://github.com/ealsur/serverless-recipes/tree/master/cosmosdboutputbindings>
Here is an example how to do it. You just need to adjust it to you needs.

```
    [FunctionName("Function1")]
    public static async Task<HttpResponseMessage> Run(
    [HttpTrigger(AuthorizationLevel.Function, "get", "post", Route = null)]HttpRequestMessage req,
    TraceWriter log)
    {
        dynamic data = await req.Content.ReadAsAsync<object>();

        var connectionString = "DbUri";
        var key = "DbKey";

        using (var client = new DocumentClient(new Uri(connectionString), key))
        {
            var collectionLink = UriFactory.CreateDocumentCollectionUri("DbName", "CollectionName");
            await client.UpsertDocumentAsync(collectionLink, data);
        }

        return req.CreateResponse(HttpStatusCode.OK);
    }

```