Support get only properties

[Mitkee]

Describe the solution you'd like Currently, get only properties is not supported in deserialization. For example:

public class MyThing {
  public int Number {get; set; }
  public int NextNumber => Number +1;
}

We can correctly write this schema, but we'll be unable to read it since NextNumber does not have a setter. As a workaround for this, the following can be done:

public class MyThing {
 public int Number {get; set;}
 public int NextNumber  {
        get => Number +1;
        init
        {
            //Ignored, set method only here to not make deserialization fail
        }
    }
}

It would be nice if get only properties would be ignored either out of the box, or if a special attribute could be added to opt in for this behavior.

Describe implementation idea How it could be done? Either we make the following case work out of the box;

public class MyThing {
  public int Number {get; set; }
  public int NextNumber => Number +1;
}

Or, a custom attribute is added to support this case:

public class MyThing {
  public int Number {get; set; }
  [ReadOnly]
  public int NextNumber => Number +1;
}

The expected outcome of both options would be that the value is written when deserializing, but it won't be populated when deserializing.

[AdrianStrugala]

Hello! Thank you for reporting this problem. I will investigate the solution. Best, Adrian

[AdrianStrugala]

Hello @Mitkee

The fix is ready. From v.3.4.2 of AvroConvert the get-only properties should not be throwing errors during deserialization.

Regards, Adrian

[Mitkee]

Awesome, thanks! 🙏

[Mitkee]

While the basic cases seem to work, it seems certain chains of interactions are causing deserialization to fail still.

using NUnit.Framework;
using SolTechnology.Avro;

namespace TestNestedReadonly;

public record Parent
{
    public List<Child> Children { get; set; } = new();
}

public record Child
{
    public List<Toy> Toys { get; set; } = new();

    //Need to clean this up
    public int? TotalPrice => Toys != null && Toys.Any() ? Toys.Sum(v => v.Price) : null;

    public int? TotalWeight => Toys!= null && Toys.Any() ? Toys.Sum(v => v.Weight) : null;
    // Uncomment this for an interesting process crash
    //public decimal? AveragePricePerWeight => Toys?.Average(t => t.PricePerWeightUnit);
}

public record Toy
{
    public string Name { get; set; }
    public int Weight { get; set; }
    public int Price { get; set; }

    public decimal PricePerWeightUnit => decimal.Round(Price / Weight, 2);
}

public class AvroReadonlyIssue
{

    [Test]
    public void TestReadonlySerializationAndDeserialization()
    {
        var parent = new Parent()
        {
            Children = new List<Child>
            {
                new Child()
                {
                    Toys = new List<Toy>()
                    {
                        new Toy()
                        {
                            Weight = 10, Price = 11, Name = "Toy1"
                        },
                        new Toy()
                        {
                            Weight = 6, Price = 2, Name = "Toy2"
                        }
                    },
                }
            }
        };
        var serialized = AvroConvert.Serialize(parent);
        var deserialized = AvroConvert.Deserialize<Parent>(serialized);
        Assert.Pass();
    }
}

Take the above test - the model is serialized properly, but deserializing gives

SolTechnology.Avro.Infrastructure.Exceptions.AvroTypeMismatchException : Unable to deserialize [Parent] of schema [Record] to the target type [TestNes...

SolTechnology.Avro.Infrastructure.Exceptions.AvroTypeMismatchException : Unable to deserialize [Parent] of schema [Record] to the target type [TestNestedReadonly.Parent]. Inner exception:
  ----> SolTechnology.Avro.Infrastructure.Exceptions.AvroTypeMismatchException : Unable to deserialize [array] of schema [Array] to the target type [System.Collections.Generic.List`1[TestNestedReadonly.Child]]. Inner exception:
  ----> SolTechnology.Avro.Infrastructure.Exceptions.AvroTypeMismatchException : Unable to deserialize [Child] of schema [Record] to the target type [TestNestedReadonly.Child]. Inner exception:
  ----> SolTechnology.Avro.Infrastructure.Exceptions.AvroTypeMismatchException : Unable to deserialize [array] of schema [Array] to the target type [System.Collections.Generic.List`1[TestNestedReadonly.Toy]]. Inner exception:
  ----> SolTechnology.Avro.Infrastructure.Exceptions.AvroTypeMismatchException : Unable to deserialize [Toy] of schema [Record] to the target type [TestNestedReadonly.Toy]. Inner exception:
  ----> SolTechnology.Avro.Infrastructure.Exceptions.AvroTypeMismatchException : Unable to deserialize [int] of schema [Int] to the target type [System.Int32]. Inner exception:
  ----> System.IO.EndOfStreamException : Attempted to read past the end of the stream.
   at SolTechnology.Avro.AvroObjectServices.Read.Resolver.Resolve(TypeSchema writerSchema, TypeSchema readerSchema, IReader reader, Type type)
   at SolTechnology.Avro.AvroObjectServices.Read.Resolver.Resolve[T](IReader reader, Int64 itemsCount)
   at SolTechnology.Avro.Features.Deserialize.Decoder.Read[T](Reader reader, Header header, AbstractCodec codec, Resolver resolver)
   at SolTechnology.Avro.Features.Deserialize.Decoder.Decode[T](Stream stream, TypeSchema readSchema)
   at SolTechnology.Avro.AvroConvert.Deserialize[T](Byte[] avroBytes)
   at TestNestedReadonly.AvroReadonlyIssue.TestReadonlySerializationAndDeserialization() in C:\Projects\nps.dataservices.auctions\NPS.DataServices.Auction.IntegrationTests\TestRepositories\AvroReadonlyIssue.cs:line 63
--AvroTypeMismatchException
   at SolTechnology.Avro.AvroObjectServices.Read.Resolver.Resolve(TypeSchema writerSchema, TypeSchema readerSchema, IReader reader, Type type)
   at SolTechnology.Avro.AvroObjectServices.Read.Resolver.ResolveRecord(RecordSchema writerSchema, RecordSchema readerSchema, IReader reader, Type type)
   at SolTechnology.Avro.AvroObjectServices.Read.Resolver.Resolve(TypeSchema writerSchema, TypeSchema readerSchema, IReader reader, Type type)
--AvroTypeMismatchException
   at SolTechnology.Avro.AvroObjectServices.Read.Resolver.Resolve(TypeSchema writerSchema, TypeSchema readerSchema, IReader reader, Type type)
   at SolTechnology.Avro.AvroObjectServices.Read.Resolver.ResolveArray(TypeSchema writerSchema, TypeSchema readerSchema, IReader reader, Type type, Int64 itemsCount)
   at SolTechnology.Avro.AvroObjectServices.Read.Resolver.Resolve(TypeSchema writerSchema, TypeSchema readerSchema, IReader reader, Type type)
--AvroTypeMismatchException
   at SolTechnology.Avro.AvroObjectServices.Read.Resolver.Resolve(TypeSchema writerSchema, TypeSchema readerSchema, IReader reader, Type type)
   at SolTechnology.Avro.AvroObjectServices.Read.Resolver.ResolveRecord(RecordSchema writerSchema, RecordSchema readerSchema, IReader reader, Type type)
   at SolTechnology.Avro.AvroObjectServices.Read.Resolver.Resolve(TypeSchema writerSchema, TypeSchema readerSchema, IReader reader, Type type)
--AvroTypeMismatchException
   at SolTechnology.Avro.AvroObjectServices.Read.Resolver.Resolve(TypeSchema writerSchema, TypeSchema readerSchema, IReader reader, Type type)
   at SolTechnology.Avro.AvroObjectServices.Read.Resolver.ResolveArray(TypeSchema writerSchema, TypeSchema readerSchema, IReader reader, Type type, Int64 itemsCount)
   at SolTechnology.Avro.AvroObjectServices.Read.Resolver.Resolve(TypeSchema writerSchema, TypeSchema readerSchema, IReader reader, Type type)
--AvroTypeMismatchException
   at SolTechnology.Avro.AvroObjectServices.Read.Resolver.Resolve(TypeSchema writerSchema, TypeSchema readerSchema, IReader reader, Type type)
   at SolTechnology.Avro.AvroObjectServices.Read.Resolver.ResolveRecord(RecordSchema writerSchema, RecordSchema readerSchema, IReader reader, Type type)
   at SolTechnology.Avro.AvroObjectServices.Read.Resolver.Resolve(TypeSchema writerSchema, TypeSchema readerSchema, IReader reader, Type type)
--EndOfStreamException
   at SolTechnology.Avro.AvroObjectServices.Read.Reader.Read()
   at SolTechnology.Avro.AvroObjectServices.Read.Reader.ReadLong()
   at SolTechnology.Avro.AvroObjectServices.Read.Reader.ReadInt()
   at SolTechnology.Avro.AvroObjectServices.Read.Resolver.ResolveInt(Type readType, IReader reader)
   at SolTechnology.Avro.AvroObjectServices.Read.Resolver.Resolve(TypeSchema writerSchema, TypeSchema readerSchema, IReader reader, Type type)

-----

One or more child tests had errors
  Exception doesn't have a stacktrace

Even more interesting - uncommenting //public decimal? AveragePricePerWeight => Toys?.Average(t => t.PricePerWeightUnit); causes the whole process to fail when deserializing. It doesn't throw out, but instead this happens:

I've a feeling something weird is still happening with the read only properties here? In basic cases, it works as expected.

[AdrianStrugala]

Well, I need to dig deeper into that. Thank you for providing the test case

[AdrianStrugala]

Hey,

The problem was with caching during the deserialization of a collection of classes with read-only properties. It should be fixed now. As for the calculated decimal property you might want to add AvroDecimal attribute:

[AvroDecimal(Precision = 28, Scale = 28)]
public decimal? AveragePricePerWeight => Toys?.Average(t => t.PricePerWeightUnit);

It's to ensure the result not exceeding max precision of avro decimal.

Best, Adrian