Update sample code for new Migrate from Newtonsoft article

snippets/core/system-text-json/csharp/IForecast.cs

@@ -0,0 +1,25 @@
+using System;
+
+namespace SystemTextJsonSamples
+{
+    public interface IForecast
+    {
+        public DateTimeOffset Date { get; set; }
+        public int TemperatureCelsius { get; set; }
+        public string Summary { get; set; }
+    }
+
+    public class Forecast : IForecast
+    {
+        public DateTimeOffset Date { get; set; }
+        public int TemperatureCelsius { get; set; }
+        public string Summary { get; set; }
+        public int WindSpeed { get; set; }
+    }
+
+    public class Forecasts
+    {
+        public IForecast Monday { get; set; }
+        public object Tuesday { get; set; }
+    }
+}

snippets/core/system-text-json/csharp/SerializePolymorphic.cs

@@ -14,35 +14,80 @@ public static void Run()
 
             Console.WriteLine("Base class generic type - derived class properties omitted");
             // <SnippetSerializeDefault>
-            var serializeOptions = new JsonSerializerOptions
+            var options = new JsonSerializerOptions
             {
                 WriteIndented = true
             };
-            jsonString = JsonSerializer.Serialize<WeatherForecast>(weatherForecast, serializeOptions);
+            jsonString = JsonSerializer.Serialize<WeatherForecast>(weatherForecast, options);
             // </SnippetSerializeDefault>
 
             Console.WriteLine($"JSON output:\n{jsonString}\n");
 
             Console.WriteLine("Object generic type parameter - derived class properties included");
             // <SnippetSerializeObject>
-            serializeOptions = new JsonSerializerOptions
+            options = new JsonSerializerOptions
             {
                 WriteIndented = true
             };
-            jsonString = JsonSerializer.Serialize<object>(weatherForecast, serializeOptions);
+            jsonString = JsonSerializer.Serialize<object>(weatherForecast, options);
             // </SnippetSerializeObject>
             Console.WriteLine($"JSON output:\n{jsonString}\n");
 
 
             Console.WriteLine("GetType() type parameter - derived class properties included");
             // <SnippetSerializeGetType>
-            serializeOptions = new JsonSerializerOptions
+            options = new JsonSerializerOptions
             {
                 WriteIndented = true
             };
-            jsonString = JsonSerializer.Serialize(weatherForecast, weatherForecast.GetType(), serializeOptions);
+            jsonString = JsonSerializer.Serialize(weatherForecast, weatherForecast.GetType(), options);
             // </SnippetSerializeGetType>
             Console.WriteLine($"JSON output:\n{jsonString}\n");
+
+            Console.WriteLine("Extra properties on interface implementations included only for object properties");
+            // <SnippetSerializeInterface>
+            var forecasts = new Forecasts
+            {
+                Monday = new Forecast
+                {
+                    Date = DateTime.Parse("2020-01-06"),
+                    TemperatureCelsius = 10,
+                    Summary = "Cool",
+                    WindSpeed = 8
+                },
+                Tuesday = new Forecast
+                {
+                    Date = DateTime.Parse("2020-01-07"),
+                    TemperatureCelsius = 11,
+                    Summary = "Rainy",
+                    WindSpeed = 10
+                }
+            };
+
+            options = new JsonSerializerOptions
+            {
+                WriteIndented = true
+            };
+            jsonString = JsonSerializer.Serialize(forecasts, options);
+            // </SnippetSerializeInterface>
+            Console.WriteLine($"{jsonString}\n");
+
+            WeatherForecastWithPrevious weatherForecastWithPrevious = WeatherForecastFactories.CreateWeatherForecastWithPrevious();
+            WeatherForecastWithPreviousAsObject weatherForecastWithPreviousAsObject = WeatherForecastFactories.CreateWeatherForecastWithPreviousAsObject();
+
+            Console.WriteLine("Second level derived class properties included only for object properties");
+            // <SnippetSerializeSecondLevel>
+            options = new JsonSerializerOptions
+            {
+                WriteIndented = true
+            };
+            jsonString = JsonSerializer.Serialize(weatherForecastWithPreviousAsObject, options);
+            // </SnippetSerializeSecondLevel>
+            Console.WriteLine($"JSON output with WindSpeed:\n{jsonString}\n");
+            jsonString = JsonSerializer.Serialize(
+                weatherForecastWithPrevious,
+                options);
+            Console.WriteLine($"JSON output without WindSpeed:\n{jsonString}\n");
         }
     }
 }

snippets/core/system-text-json/csharp/Utf8ReaderFromFile.cs

@@ -10,7 +10,7 @@ public class Utf8ReaderFromFile
         private static readonly byte[] s_nameUtf8 = Encoding.UTF8.GetBytes("name");
         public static void Run()
         {
-            // Read as UTF-16 and transcode to UTF-8 to convert to a Span<byte>
+            // Read as UTF-16 and transcode to UTF-8 to convert to a ReadOnlySpan<byte>
             string fileName = "Universities.json";
             string jsonString = File.ReadAllText(fileName);
             ReadOnlySpan<byte> jsonReadOnlySpan = Encoding.UTF8.GetBytes(jsonString);
@@ -22,23 +22,23 @@ public static void Run()
             int count = 0;
             int total = 0;
 
-            var json = new Utf8JsonReader(jsonReadOnlySpan, isFinalBlock: true, state: default);
+            var reader = new Utf8JsonReader(jsonReadOnlySpan);
 
-            while (json.Read())
+            while (reader.Read())
             {
-                JsonTokenType tokenType = json.TokenType;
+                JsonTokenType tokenType = reader.TokenType;
 
                 switch (tokenType)
                 {
                     case JsonTokenType.StartObject:
                         total++;
                         break;
                     case JsonTokenType.PropertyName:
-                        if (json.ValueTextEquals(s_nameUtf8))
+                        if (reader.ValueTextEquals(s_nameUtf8))
                         {
                             // Assume valid JSON, known schema
-                            json.Read();
-                            if (json.GetString().EndsWith("University"))
+                            reader.Read();
+                            if (reader.GetString().EndsWith("University"))
                             {
                                 count++;
                             }

snippets/core/system-text-json/csharp/WeatherForecast.cs

@@ -13,6 +13,26 @@ public class WeatherForecast
     }
     // </SnippetWF>
 
+    // <SnippetWFWithPrevious>
+    public class WeatherForecastWithPrevious
+    {
+        public DateTimeOffset Date { get; set; }
+        public int TemperatureCelsius { get; set; }
+        public string Summary { get; set; }
+        public WeatherForecast PreviousForecast { get; set; }
+    }
+    // </SnippetWFWithPrevious>
+
+    // <SnippetWFWithPreviousAsObject>
+    public class WeatherForecastWithPreviousAsObject
+    {
+        public DateTimeOffset Date { get; set; }
+        public int TemperatureCelsius { get; set; }
+        public string Summary { get; set; }
+        public object PreviousForecast { get; set; }
+    }
+    // </SnippetWFWithPreviousAsObject>
+
     // <SnippetWFWithLong>
     public class WeatherForecastWithLong
     {
@@ -306,6 +326,30 @@ public static WeatherForecast CreateWeatherForecast()
             return weatherForecast;
         }
 
+        public static WeatherForecastWithPrevious CreateWeatherForecastWithPrevious()
+        {
+            var weatherForecast = new WeatherForecastWithPrevious
+            {
+                Date = DateTime.Parse("2019-08-01"),
+                TemperatureCelsius = 25,
+                Summary = "Hot",
+                PreviousForecast = CreateWeatherForecastDerived()
+            };
+            return weatherForecast;
+        }
+
+        public static WeatherForecastWithPreviousAsObject CreateWeatherForecastWithPreviousAsObject()
+        {
+            var weatherForecast = new WeatherForecastWithPreviousAsObject
+            {
+                Date = DateTime.Parse("2019-08-01"),
+                TemperatureCelsius = 25,
+                Summary = "Hot",
+                PreviousForecast = CreateWeatherForecastDerived()
+            };
+            return weatherForecast;
+        }
+
         public static WeatherForecastWithLong CreateWeatherForecastWithLong()
         {
             var weatherForecast = new WeatherForecastWithLong