Exception is thrown when deserializing nullable strongly-typed id

[hankovich]

[StronglyTypedId]
public partial struct GroupId
{
}

public class User
{
    public User(GroupId? groupId)
    {
        GroupId = groupId;
    }

    public GroupId? GroupId { get; }
}

var json = JsonConvert.SerializeObject(new User(groupId: null)); // "{\"GroupId\":null}"
var deserialize = JsonConvert.DeserializeObject<User>(json); // throws Newtonsoft.Json.JsonSerializationException: 'Error converting value {null} to type 'System.Guid'. Path 'GroupId', line 1, position 15.'

The issue is caused by Newtonsoft.Json's behaviour (ReadJson is called on GroupIdNewtonsoftJsonConverter with objectType = Nullable<GroupId>).

A couple of related issues from Newtonsoft.Json:
JamesNK/Newtonsoft.Json#1783
JamesNK/Newtonsoft.Json#2219

Version of StronglyTypeId: 0.2.1
Version of Newtonsoft.Json: tried with both 12.0.3 and 13.0.1

[mvarendorff2]

Just hit this as well today; I would be willing to implement a fix to this @andrewlock but I have no idea where to start, honestly. Could you give me a pointer or two? Or would that effort not be worth it given that you are working on a 1.x version of this package?

[andrewlock]

I believe this is fixed in the latest beta: https://www.nuget.org/packages/StronglyTypedId/1.0.0-beta02, would you mind giving that a try? Make sure to check out this post for breaking changes etc: https://andrewlock.net/rebuilding-stongly-typed-id-as-a-source-generator-1-0-0-beta-release/#breaking-changes

[mvarendorff2]

Hey Andrew, thanks for the quick response! Unfortunately it seems that the issue is not fixed in that version. On top of that the deserializing code uses int for deserializing for a long backed id.

Starting from:

using StronglyTypedIds;

namespace ExampleIds {
    [StronglyTypedId(StronglyTypedIdBackingType.Long, StronglyTypedIdConverter.NewtonsoftJson)]
    public partial struct ExampleId { }
}

the generated code of the ReadJson function (rest omitted for brevity) looks like this:

public override object ReadJson(Newtonsoft.Json.JsonReader reader, System.Type objectType, object existingValue, Newtonsoft.Json.JsonSerializer serializer)
{
    return new ExampleId(serializer.Deserialize<int>(reader));
}

while I would expect it to be something more like this (using long? for deserializing and returning null in the case of a null value read):

public override object? ReadJson(Newtonsoft.Json.JsonReader reader, System.Type objectType, object existingValue, Newtonsoft.Json.JsonSerializer serializer)
{
    var deserializeResult = serializer.Deserialize<long?>(reader);
    return deserializeResult == null ? null : new ExampleId(deserializeResult.Value);
}

[andrewlock]

Hey @mvarendorff, you're absolutely right, this is still outstanding.

I've been working on it this evening, and I've fixed the bug in 13f91b1.

I haven't released a new package yet, as there's some other issues I want to tackle at the same time (namely #38, and upgrading to .NET 6 incremental generators), but I should have a new version out soon