在函数中显式地将字符串转换为GUID。例如，使用Guid.Parse()方法将字符串转换为GUID。示例代码如下：

public static async Task Run(
    [HttpTrigger(AuthorizationLevel.Function, "post", Route = null)] HttpRequest req,
    [CosmosDB(
        databaseName: "database-name",
        collectionName: "collection-name",
        ConnectionStringSetting = "connection-string",
        Id = "{Query.id}",
        PartitionKey = "{Query.partitionKey}")] MyObject inputDocument,
    ILogger log)
{
    // Convert string id to Guid
    if(Guid.TryParse(req.Query["id"], out Guid id))
    {
        inputDocument.Id = id;
    }
    else
    {
        return new BadRequestObjectResult("Invalid id parameter");
    }

    // rest of the function code
    // ...

    return new OkObjectResult("Success");
}