JsonSerializer: Allow out-of-order reading of metadata properties. #72604
Description
EDIT See #72604 (comment) for an API proposal.
Description
Attempting to deserialize a polymorphic structure with System.Text.Json that doesn't feature $type at start of the object results in an exception.
For my scenario, this currently prevents me from using the built-in polymorphism support with jsonb columns in Postgres, as object properties have no guaranteed order.
Developer comment on this issue: #63747 (comment)
Reproduction Steps
var databaseState = @"{
""BaseDictionary"": {
""6ed6e524-2ca4-4fea-8e21-7245ccb61863"": {
""Id"": ""6ed6e524-2ca4-4fea-8e21-7245ccb61863"",
""Name"": ""Something"",
""$type"": ""Derived"",
""OtherGuid"": ""d471c77d-5412-4e7a-a98d-8304e87792ed""
}
}
}";
JsonSerializer.Deserialize<WrapperType>(databaseState);
public record WrapperType(Dictionary<Guid, WrapperType.Base> BaseDictionary)
{
[JsonDerivedType(typeof(Derived), nameof(Derived))]
[JsonDerivedType(typeof(AlsoDerived), nameof(AlsoDerived))]
public abstract record Base(Guid Id, string Name);
public record Derived(Guid Id, string Name, Guid OtherGuid): Base(Id, Name);
public record AlsoDerived(Guid Id, string Name) : Base(Id, Name);
}Expected behavior
Deserialization should work.
Actual behavior
System.NotSupportedException: 'Deserialization of types without a parameterless constructor, a singular parameterized constructor, or a parameterized constructor annotated with 'JsonConstructorAttribute' is not supported.
Regression?
Limitation of initial implementation
Known Workarounds
I currently use PolyJson as an alternative, as the implementation reads ahead to find the discriminator.
Configuration
Impacts any version of STJ 7.0
Other information
No response