'DynamoDbContext.LoadAsync' does not respect 'DynamoDBOperationConfig.IndexName'

[julealgon]

Description

When using the LoadAsync method on IDynamoDbContext to load an entity using a secondary global index, I'm getting unexpected behavior: an InvalidCastException is being thrown.

Switching the exact same call to a QueryAsync fixes the problem.

I believe LoadAsync is not respecting the IndexName property on the configuration object and is using the primary index for all searches. Either the API is incredibly misleading (as it allows you to pass this unused value) or there is a bug there.

Reproduction Steps

1. Create a table with a primary and a secondary index
2. Map the primary key to a Guid property
3. Map the secondary key to a string property

    [DynamoDBTable("Somethings")]
    internal sealed class Something
    {
        [DynamoDBHashKey]
        public Guid? Id { get; set; }

        [DynamoDBGlobalSecondaryIndexHashKey]
        public string? Name { get; set; }
    }

4. Try to use LoadAsync with a string key and pass new DynamoDBOperationConfig { IndexName = <Name_Of_Secondary_Index> } as options

await dynamoDBContext.LoadAsync<Something>("someName", new DynamoDBOperationConfig { IndexName = "Name-index" });

5. An InvalidCastException is thrown
6. Replace the LoadAsync call with QueryAsync, and it works as expected:

var query = dynamoDBContext.QueryAsync<Something>("someName", new DynamoDBOperationConfig { IndexName = "Name-index" });
await query.GetNextSetAsync();

Logs

System.InvalidCastException: Unable to cast object of type 'System.String' to type 'System.Guid'.
at Amazon.DynamoDBv2.Converter`1.TryTo(Object value, Primitive& p)
at Amazon.DynamoDBv2.Converter.TryToEntry(Object value, DynamoDBEntry& entry)
at Amazon.DynamoDBv2.Converter.ToEntry(Object value)
at Amazon.DynamoDBv2.DynamoDBEntryConversion.ConvertToEntry(Type inputType, Object value)
at Amazon.DynamoDBv2.DataModel.DynamoDBContext.ToDynamoDBEntry(SimplePropertyStorage propertyStorage, Object value, DynamoDBFlatConfig flatConfig, Boolean canReturnScalarInsteadOfList)
at Amazon.DynamoDBv2.DataModel.DynamoDBContext.ToDynamoDBEntry(SimplePropertyStorage propertyStorage, Object value, DynamoDBFlatConfig flatConfig)
at Amazon.DynamoDBv2.DataModel.DynamoDBContext.ValueToDynamoDBEntry(PropertyStorage propertyStorage, Object value, DynamoDBFlatConfig flatConfig)
at Amazon.DynamoDBv2.DataModel.DynamoDBContext.MakeKey(Object hashKey, Object rangeKey, ItemStorageConfig storageConfig, DynamoDBFlatConfig flatConfig)
at Amazon.DynamoDBv2.DataModel.DynamoDBContext.LoadHelperAsync[T](Object hashKey, Object rangeKey, DynamoDBOperationConfig operationConfig, CancellationToken cancellationToken)
at Amazon.DynamoDBv2.DataModel.DynamoDBContext.LoadAsync[T](Object hashKey, DynamoDBOperationConfig operationConfig, CancellationToken cancellationToken)

Environment

• SDK Version: AWSSDK.Core Version="3.5.1.39"
• Package Version: AWSSDK.DynamoDBv2 Version="3.5.3.3"
• OS Info: Windows 10
• Build Environment Visual Studio 2019 16.8.1
• Targeted .NET Platform: Net Core 3.1

Resolution

• 👋 I can/would-like-to implement a fix for this problem myself

I belive LoadAsync should be changed to respect the index being passed as a parameter and use the object hashKey against that.

---

This is a 🐛 bug-report

[ashishdhingra]

Hi @julealgon,

Good afternoon.

Please refer to the page .NET: Object Persistence Model -> Supported Data Types for the list of supported data types. Looks like Guid is not the supported data type. Refer to page Mapping Arbitrary Data with DynamoDB Using the AWS SDK for .NET Object Persistence Model for example on how support arbitrary data types. Basically it involves developing custom TypeCpnverter.

As a workaround, you may use string instead of Guid type for Id property. For using Guid type, modifying your code to below works fine:

using Amazon.DynamoDBv2;
using Amazon.DynamoDBv2.DataModel;
using Amazon.DynamoDBv2.DocumentModel;
using System;

namespace DynamoDbSecondaryIndexTest1748
{
    class Program
    {
        static void Main(string[] args)
        {
            AmazonDynamoDBClient amazonDynamoDBClient = new AmazonDynamoDBClient();
            DynamoDBContext dynamoDBContext = new DynamoDBContext(amazonDynamoDBClient);
            
            var loadResult = dynamoDBContext.LoadAsync<Something>("75f05566-2209-4f3d-ba5a-cfd9da5eab62", new DynamoDBOperationConfig { IndexName = "Name-index" }).GetAwaiter().GetResult();

            Console.WriteLine("Loaded Result: " + loadResult);
        }
    }

    [DynamoDBTable("TestTable")]
    internal sealed class Something
    {
        [DynamoDBHashKey]
        [DynamoDBProperty(typeof(GuidTypeConverter))]
        public Guid Id { get; set; }
        
        [DynamoDBGlobalSecondaryIndexHashKey]
        public string Name { get; set; }

        public override string ToString()
        {
            return $"[Id: {Id}, Name: {Name}]";
        }
    }

    public class GuidTypeConverter : IPropertyConverter
    {
        public DynamoDBEntry ToEntry(object value)
        {
            if(value == null || !(value is Guid)) throw new ArgumentOutOfRangeException();

            DynamoDBEntry entry = new Primitive
            {
                Value = ((Guid)value).ToString()
            };

            return entry;
        }

        public object FromEntry(DynamoDBEntry entry)
        {
            Primitive primitive = entry as Primitive;
            Guid guidValue;
            if (primitive == null || !(primitive.Value is String) || string.IsNullOrEmpty((string)primitive.Value) || !Guid.TryParse((string)primitive.Value, out guidValue))
                throw new ArgumentOutOfRangeException();

            return guidValue;
        }
    }
}

NOTE: The above code should be used only for reference. Kindly validate and test the GuidTypeConverter logic before trying to use the Guid type converter. We are not responsible for any data loss or production issues.

Please let me know if this helps and if this issue could be closed.

Thanks,
Ashish

[julealgon]

@ashishdhingra I believe you might have misunderstood my request here. Please note that Guid is working fine when loading and saving entities. I have both the primary key, as well as another property on my model, mapped as Guid.

The problem here happens with the global secondary index, which has a string mapped property. Once I try to use LoadAsync passing a string value and the name of the secondary index, I get the exception above which is attempting to convert my string argument into Guid (which does not make sense since I'm not querying on the primary index).

I kindly request that you take another look at this. Even if the page you provided doesn't mention Guid as a supported type, I believe the issue here is not directly related to that.

[julealgon]

Also @ashishdhingra , I'd suggest to avoid providing example source code where you block on async code, as that is a bad practice that can lead to hard to debug problems in .Net. In your sample Main, you could just make Main itself async.

People not aware of the issues might end up naively copying those code sections into their code.

[ashishdhingra]

Hi @julealgon,

Good morning.

Thanks for your inputs. I used your code exactly where it tries to use the secondary index, to reproduce the issue. When not using the type converter, the QueryAsync call didn't throw any exception, but it also didn't returned any result. The LoadAsync call threw the type cast exception mentioned. After the use of type converter, the LoadAsync call (with the secondary index as 2nd parameter), worked properly. I will try to pinpoint the exact code in SDK which throws the error.

In the mean while, in order to get proper understanding of the issue, please share the following:

1. Exact DynamoDB column configuration in AWS Console and the sample code which is working fine for you when loading and saving entities, without use of a type converter.

2. Reconfirm what you meant by The problem here happens with the global secondary index, which has a string mapped property. Once I try to use LoadAsync passing a string value and the name of the secondary index,. I guess you are referring to the code below (which is what I used exactly):

dynamoDBContext.LoadAsync<Something>("75f05566-2209-4f3d-ba5a-cfd9da5eab62", new DynamoDBOperationConfig { IndexName = "Name-index" })

Regarding the example code where I'm blocking async call, that is just for reference purposes as mentioned in the note. I agree with your assertion that we should not block async calls in live production code.

Thanks,
Ashish