NET 8 – Serializing properties from interface hierarchies

.NET 8 adds support for serializing properties from interface hierarchies. This means that all the properties from all interfaces in the hierarchy will be included in the serialization. The most important thing is where you start.

Let’s take the following hierarchy as an example:

public interface IBase
{
    public int Base { get; set; }
}

public interface IDerived : IBase
{
    public int Derived { get; set; }
}

public interface IDerived2 : IDerived
{
    public int Derived2 { get; set; }
}

public class Derived2Impl : IDerived2
{
    public int Base { get; set; }
    public int Derived { get; set; }
    public int Derived2 { get; set; }
}
Code language: C# (cs)

Now, during serialization, if you pass along a Derived2Impl instance stored in a IDerived2 variable, all 3 properties from the hierarchy will be serialized.

IDerived2 value = new Derived2Impl { Base = 0, Derived = 1, Derived2 = 2 };

JsonSerializer.Serialize(value);
// Output: {"Derived2":2,"Derived":1,"Base":0}
Code language: C# (cs)

If instead you define your variable to be of type IDerived, only 2 properties will be serialized.

IDerived value = new Derived2Impl { Base = 0, Derived = 1, Derived2 = 2 };

JsonSerializer.Serialize(value);
// Output: {"Derived":1,"Base":0}
Code language: C# (cs)

And for an IBase variable, as expected, only one property will be serialized, despite the fact that the object we’re deserializing is of type Derived2Impl – has all 3 interfaces implemented, thus all 3 properties defined.

IBase value = new Derived2Impl { Base = 0, Derived = 1, Derived2 = 2 };

JsonSerializer.Serialize(value);
// Output: {"Base":0}
Code language: C# (cs)