Azure Function V4 how to read/write to a CosmosDB

Question

I have two Azure Functions running in dotnet-isolated mode that I am upgrading to V4 (they were V3 dotnet mode). The functions used the old WebJobs namespace using the [CosmosDB] attribute in the function definition.

Unfortunately, this attribute is no longer supported in dotnet-isolated mode as I am now using the Microsoft.Azure.Functions.Worker namespaces; it appears that the existing documentation that I can find on Azure functions has not been updated.

How do I read and write to Cosmos DB using an Azure Function activated by an HTTP Trigger in dotnet-isolated mode?

Basically, I have a read function which takes a documentId, looks it up and returns the record as a MyDoc, and a write function which takes a MyDoc and writes the fields into cosmos db.

Regards.

Answer 1

Based on Microsoft Documentation its available in package :

Microsoft.Azure.Functions.Worker.Extensions.CosmosDB

here is working example from Microsoft documentation with azure function v 4 isolated mode For Input :

[Function(nameof(DocByIdFromJSON))]
public void DocByIdFromJSON(
    [QueueTrigger("todoqueueforlookup")] ToDoItemLookup toDoItemLookup,
    [CosmosDBInput(
        databaseName: "ToDoItems",
        containerName: "Items",
        Connection  = "CosmosDBConnection",
        Id = "{ToDoItemId}",
        PartitionKey = "{ToDoItemPartitionKeyValue}")] ToDoItem toDoItem)
{
    _logger.LogInformation($"C# Queue trigger function processed Id={toDoItemLookup?.ToDoItemId} Key={toDoItemLookup?.ToDoItemPartitionKeyValue}");

    if (toDoItem == null)
    
        _logger.LogInformation($"ToDo item not found");
    }
    else
    {
        _logger.LogInformation($"Found ToDo item, Description={toDoItem.Description}");
    }
}

here is a link also for the documentation: https://learn.microsoft.com/en-us/azure/azure-functions/functions-bindings-cosmosdb-v2-input?tabs=python-v2%2Cisolated-process%2Cnodejs-v4%2Cextensionv4&pivots=programming-language-csharp

and for output binding:

 [FunctionName("WriteOneDoc")]
    public static void Run(
        [QueueTrigger("todoqueueforwrite")] string queueMessage,
        [CosmosDB(
            databaseName: "ToDoItems",
            containerName: "Items",
            Connection = "CosmosDBConnection")]out dynamic document,
        ILogger log)
    {
        document = new { Description = queueMessage, id = Guid.NewGuid() };

        log.LogInformation($"C# Queue trigger function inserted one row");
        log.LogInformation($"Description={queueMessage}");
    }

Link also for Output Binding documentation