System.InvalidCastException: Specified cast is not valid. - DynamoDB Query

Question

I'm trying to Query a DynamoDB table and I'm using Xamarin.Forms. I have a "Cart" class set up and I'm trying to retrive a specific set of carts. Here is the code:

    [DynamoDBTable("Carts")]
    public class Cart
    {
        [DynamoDBHashKey]
        public string Name { get; set; }
        public string Subtitle { get; set; }

        public static async Task<List<Cart>> GetAll()
        {
            CognitoAWSCredentials Credentials = new CognitoAWSCredentials(
                   "us-west-2:xxxxxx-xxxx-xxxx-xxxx-xxxxxxxxx",
                   RegionEndpoint.USWest2
               );
            AmazonDynamoDBClient Client = new AmazonDynamoDBClient(Credentials, RegionEndpoint.USWest2);
            DynamoDBContext Context = new DynamoDBContext(Client);
            DynamoDBOperationConfig config = new DynamoDBOperationConfig();

            List<ScanCondition> filter = new List<ScanCondition>() 
                { new ScanCondition("Name", ScanOperator.Equal, "NameOfCart") };
            config.QueryFilter = filter;
            AsyncSearch<Cart> asyncsearch = Context.QueryAsync<Cart>(config);
            //AsyncSearch<Cart> asyncsearch = Context.ScanAsync<Cart>(null);
            List<Cart> carts = await asyncsearch.GetRemainingAsync();
            return carts;
        }
}

When I hit "Context.QueryAsync" I get a "System.InvalidCastException: Specified cast is not valid." Exception. The line I commented out below it (ScanAsync) works just fine and returns the full list of carts in the table. This however is really slow and I only want to see a certain list of carts.

Any help would be greatly appreciated! Thanks much!

Answer 1

Context.QueryAsync<Cart>(config); This was returning nothing and therefore the exception was thrown. If I run Context.QueryAsync<Cart>("nameofcart"); it runs fine for some reason and just returns one value. Still can't figure out how to get multiple items based on a query.