C# JSON DB Column with update callback

FooBar.cs

namespace Foo.Bar;

public class FooBar : JsonColumn
{
    public string? FooBar
    {
        get => GetValue<string?>("fooBar", null);
        set => SetValue("fooBar", value);
    }
}

JsonColumn.cs

using System.Text.Json;

namespace Foo.Bar;

public abstract class JsonColumn
{
    protected Dictionary<string,object> obj = new Dictionary<string, object>();
    protected Action<string>? onChange;

    public static T Create<T>(string? json, Action<string> onChange)
        where T : JsonColumn, new()
    {
        if (json != null)
        {
            var obj = JsonSerializer.Deserialize<Dictionary<string, object>>(json)!;
            return new T()
            {
                obj = obj,
                onChange = onChange
            };
        }
        else
        {
            return new T()
            {
                onChange = onChange
            };
        }
    }

    protected T GetValue<T>(string name, T @default)
    {
        if (obj.ContainsKey(name))
        {
            return (T)obj[name];
        }

        return @default;
    }

    protected void SetValue<T>(string name, T val)
    {
        if (val != null)
        {
            obj[name] = val;
        }
        else if (obj.ContainsKey(name))
        {
            obj.Remove(name);
        }

        var json = JsonSerializer.Serialize(obj);
        onChange?.Invoke(json);
    }
}

MyTable.cs

namespace Foo.Bar;

[Table("MyTable")]
public class MyTable
{
    [Column("fooBarJson")]
    public string? FooBarJson { get; set; }
    
    [NotMapped]
    public FooBar FooBar => FooBar.Create<FooBar>(
        FooBarJson,
        json => FooBarJson = json
    );
}