Json.NET无法序列化集合字典

Question

I'm trying to serialize (and later on deserialize) a Dictionary<string, ISet<string>> . Unfortunately, Json.NET (v6.0.3 via NuGet) fails to do this. What I do is

var value = new Dictionary<string, ISet<string>>
    {
        {"foo", new HashSet<string>{"bar"}}
    };
var settings = new JsonSerializerSettings
    {
        TypeNameHandling = TypeNameHandling.Objects,
        TypeNameAssemblyFormat = FormatterAssemblyStyle.Simple
    };
var json = JsonConvert.SerializeObject(value, settings);

The variable json then holds the string

{"$type":"System.Collections.Generic.Dictionary`2[[System.String, mscorlib],[System.Collections.Generic.ISet`1[[System.String, mscorlib]], System]], mscorlib","foo":["bar"]}

Now I want to deserialize the string with

JsonConvert.DeserializeObject<IDictionary<string, ISet<string>>>(json, settings);

which fails in resolving the Dictionary type, because it cannot find the System assembly that ISet belongs to. When I instead do the following

JsonConvert.DeserializeObject<IDictionary<string, ISet<string>>>(json);

everything works just fine. So it appears that the TypeNameHandling setting (changing/omitting the format does not change anything) actually breaks deserialization.

I found that, if I don't set the TypeNameHandling settings, the serialized $type properties are simply ignored. Ie, when deserializing, the type information is taken solely from the target type where they are resolved. This works.

When setting the TypeNameHandling , type resolution happens via reflection within the Json.NET assembly, which does not have a dependency on the System assembly and therefore fails to resolve the ISet interface. I can fix this by registering on AppDomain.CurrentDomain.AssemblyResolve and resolving the assembly like so

if (args.Name == "System")
{
     return typeof (ISet<>).Assembly;
}

but this seems very fragile to me, as it solves the problem for only this one specific assembly and I have to add another case for every assembly I need somewhere.

Does anyone have experience on how to solve this? Any help is greatly appreciated!

Answer 1

Similar problem was addressed in the following thread: How can I deserialize with TypeNameHandling.Objects in Json.NET Silverlight?

The problem seems to be that Json is failing to load the assembly with partial name. You could overcome this issue by using TypeNameAssemblyFormat = FormatterAssemblyStyle.Full .

Answer 2

If you check the source code for NewtonSoft.Json in DefaultSerializationBinder.GetTypeNameFromTypeNameKey approx. row 83.. It tries to get the type

System.Collections.Generic.Dictionary 2[[System.String, mscorlib],[System.Collections.Generic.ISet 1[[System.String, mscorlib]], System]]

from assembly

mscorlib.dll

Type type = assembly.GetType(typeName);

Which returns null. This is with FormatterAssemblyStyle.Simple.

If you use FormatterAssemblyStyle.Full then the same type will be:

System.Collections.Generic.Dictionary 2[[System.String, mscorlib, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089],[System.Collections.Generic.ISet 1[[System.String, mscorlib, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089]], System, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089]]

And then:

Type type = assembly.GetType(typeName);

Will work and hence the deserialization works as well.

I cant say why this is the case though.