Add System.Text.Json support in DTO generation

src/NJsonSchema.CodeGeneration.CSharp/CSharpGeneratorSettings.cs

@@ -33,6 +33,7 @@ public CSharpGeneratorSettings()
             DictionaryBaseType = "System.Collections.Generic.Dictionary";
 
             ClassStyle = CSharpClassStyle.Poco;
+            JsonLibrary = CSharpJsonLibrary.NewtonsoftJson;
 
             RequiredPropertiesMustBeDefined = true;
             GenerateDataAnnotations = true;
@@ -99,6 +100,9 @@ public CSharpGeneratorSettings()
         /// <summary>Gets or sets the CSharp class style (default: 'Poco').</summary>
         public CSharpClassStyle ClassStyle { get; set; }
 
+        /// <summary>Gets or sets the CSharp JSON library to use (default: 'NewtonsoftJson', 'SystemTextJson' is experimental/not complete).</summary>
+        public CSharpJsonLibrary JsonLibrary { get; set; }
+
         /// <summary>Gets or sets the access modifier of generated classes and interfaces (default: 'public').</summary>
         public string TypeAccessModifier { get; set; }
 

src/NJsonSchema.CodeGeneration.CSharp/CSharpJsonLibrary.cs

@@ -0,0 +1,20 @@
+//-----------------------------------------------------------------------
+// <copyright file="CSharpClassStyle.cs" company="NJsonSchema">
+//     Copyright (c) Rico Suter. All rights reserved.
+// </copyright>
+// <license>https://github.com/RicoSuter/NJsonSchema/blob/master/LICENSE.md</license>
+// <author>Rico Suter, mail@rsuter.com</author>
+//-----------------------------------------------------------------------
+
+namespace NJsonSchema.CodeGeneration.CSharp
+{
+    /// <summary>The CSharp JSON library to use.</summary>
+    public enum CSharpJsonLibrary
+    {
+        /// <summary>Use Newtonsoft.Json</summary>
+        NewtonsoftJson, 
+
+        /// <summary>Use System.Text.Json</summary>
+        SystemTextJson
+    }
+}

src/NJsonSchema.CodeGeneration.CSharp/CSharpJsonSerializerGenerator.cs

@@ -24,8 +24,16 @@ public static string GenerateJsonSerializerParameterCode(CSharpGeneratorSettings
             var hasJsonConverters = jsonConverters.Any();
 
             var useSettingsTransformationMethod = !string.IsNullOrEmpty(settings.JsonSerializerSettingsTransformationMethod);
+            return settings.JsonLibrary == CSharpJsonLibrary.SystemTextJson ?
+                string.Empty : // TODO(system.text.json): What to do here?
+                GenerateForNewtonsoftJson(settings, jsonConverters, hasJsonConverters, useSettingsTransformationMethod);
+        }
+
+        private static string GenerateForNewtonsoftJson(CSharpGeneratorSettings settings, List<string> jsonConverters, bool hasJsonConverters, bool useSettingsTransformationMethod)
+        {
             if (settings.HandleReferences || useSettingsTransformationMethod)
             {
+                // TODO(system.text.json): Also support System.Text.Json
                 return ", " +
                        (useSettingsTransformationMethod ? settings.JsonSerializerSettingsTransformationMethod + "(" : string.Empty) +
                        "new Newtonsoft.Json.JsonSerializerSettings { " +

src/NJsonSchema.CodeGeneration.CSharp/Models/ClassTemplateModel.cs

@@ -50,6 +50,9 @@ public ClassTemplateModel(string typeName, CSharpGeneratorSettings settings,
             }
         }
 
+        /// <summary>Gets a value indicating whether to use System.Text.Json</summary>
+        public bool UseSystemTextJson => _settings.JsonLibrary == CSharpJsonLibrary.SystemTextJson;
+
         /// <summary>Gets or sets the class name.</summary>
         public override string ClassName { get; }
 

src/NJsonSchema.CodeGeneration.CSharp/Templates/Class.Constructor.Record.liquid

@@ -8,7 +8,11 @@
 {% assign sortedProperties = AllProperties | sort: "Name" -%}
 {% assign sortedParentProperties = parentProperties | sort: "Name" -%}
 
+{% if UseSystemTextJson -%}
+[System.Text.Json.Serialization.JsonConstructor]
+{% else -%}
 [Newtonsoft.Json.JsonConstructor]
+{% endif -%}
 {% if IsAbstract %}protected{% else %}public{% endif %} {{ClassName}}({% for property in sortedProperties -%}{% if skipComma -%}{% assign skipComma = false %}{% else %}, {% endif -%} {{ property.Type }} @{{ property.Name | lowercamelcase }}{% endfor -%})
 {% assign skipComma = true -%}
 {% if HasInheritance -%}

src/NJsonSchema.CodeGeneration.CSharp/Templates/Class.FromJson.liquid

@@ -1,4 +1,8 @@
 public static {{ ClassName }} FromJson(string data)
 {
+{% if UseSystemTextJson -%}
+    return System.Text.Json.JsonSerializer.Deserialize<{{ ClassName }}>(data{{ JsonSerializerParameterCode }});
+{% else -%}
     return Newtonsoft.Json.JsonConvert.DeserializeObject<{{ ClassName }}>(data{{ JsonSerializerParameterCode }});
+{% endif -%}
 }

src/NJsonSchema.CodeGeneration.CSharp/Templates/Class.ToJson.liquid

@@ -1,4 +1,8 @@
 public string ToJson() 
 {
+{% if UseSystemTextJson -%}
+    return System.Text.Json.JsonSerializer.Serialize(this{{ JsonSerializerParameterCode }});
+{% else -%}
     return Newtonsoft.Json.JsonConvert.SerializeObject(this{{ JsonSerializerParameterCode }});
+{% endif -%}
 }

src/NJsonSchema.CodeGeneration.CSharp/Templates/Class.liquid

@@ -2,7 +2,11 @@
 /// <summary>{{ Description | csharpdocs }}</summary>
 {% endif -%}
 {% if HasDiscriminator -%}
+{% if UseSystemTextJson -%}
+[JsonInheritanceConverter(typeof({{ ClassName }}), "{{ Discriminator }}")]
+{% else -%}
 [Newtonsoft.Json.JsonConverter(typeof(JsonInheritanceConverter), "{{ Discriminator }}")]
+{% endif -%}
 {% for derivedClass in DerivedClasses -%}
 {% if derivedClass.IsAbstract != true -%}
 [JsonInheritanceAttribute("{{ derivedClass.Discriminator }}", typeof({{ derivedClass.ClassName }}))]
@@ -11,7 +15,11 @@
 {% endif -%}
 [System.CodeDom.Compiler.GeneratedCode("NJsonSchema", "{{ ToolchainVersion }}")]
 {% if InheritsExceptionSchema -%}
+{%   if UseSystemTextJson -%}
+// TODO(system.text.json): What to do here?
+{%   else -%}
 [Newtonsoft.Json.JsonObjectAttribute]
+{%   endif -%}
 {% endif -%}
 {% if IsDeprecated -%}
 [System.Obsolete{% if HasDeprecatedMessage %}({{ DeprecatedMessage | literal }}){% endif %}]
@@ -20,7 +28,7 @@
 {{ TypeAccessModifier }} {% if IsAbstract %}abstract {% endif %}partial class {{ClassName}} {% template Class.Inheritance %}
 {
 {% if IsTuple -%}
-    public {{ClassName}}({% for tupleType in TupleTypes -%}{{ tupleType }} item{{ forloop.index }}{% if forloop.last == false %}, {% endif %}{% endfor -%}) : base({% for tupleType in TupleTypes -%}item{{ forloop.index }}{% if forloop.last == false %}, {% endif %}{% endfor -%})
+    public {{ ClassName }}({% for tupleType in TupleTypes -%}{{ tupleType }} item{{ forloop.index }}{% if forloop.last == false %}, {% endif %}{% endfor -%}) : base({% for tupleType in TupleTypes -%}item{{ forloop.index }}{% if forloop.last == false %}, {% endif %}{% endfor -%})
     {
     }
 
@@ -40,7 +48,14 @@
 {%   if property.HasDescription -%}
     /// <summary>{{ property.Description | csharpdocs }}</summary>
 {%   endif -%}
+{% if UseSystemTextJson -%}
+    [System.Text.Json.Serialization.JsonPropertyName("{{ property.Name }}"]
+{%   if property.IsStringEnumArray -%}
+    // TODO(system.text.json): Add string enum item converter
+{%   endif -%}
+{% else -%}
     [Newtonsoft.Json.JsonProperty("{{ property.Name }}", Required = {{ property.JsonPropertyRequiredCode }}{% if property.IsStringEnumArray %}, ItemConverterType = typeof(Newtonsoft.Json.Converters.StringEnumConverter){% endif %})]
+{% endif -%}
 {%   if property.RenderRequiredAttribute -%}
     [System.ComponentModel.DataAnnotations.Required{% if property.AllowEmptyStrings %}(AllowEmptyStrings = true){% endif %}]
 {%   endif -%}
@@ -60,10 +75,18 @@
     [System.ComponentModel.DataAnnotations.RegularExpression(@"{{ property.RegularExpressionValue }}")]
 {%   endif -%}
 {%   if property.IsStringEnum -%}
+{%     if UseSystemTextJson -%}
+    [System.Text.Json.Serialization.JsonConverter(System.Text.Json.Serialization.JsonStringEnumConverter)]
+{%     else -%}
     [Newtonsoft.Json.JsonConverter(typeof(Newtonsoft.Json.Converters.StringEnumConverter))]
+{%     endif -%}
 {%   endif -%}
 {%   if property.IsDate and UseDateFormatConverter -%}
+{%     if UseSystemTextJson -%}
+    [System.Text.Json.Serialization.JsonConverter(typeof(DateFormatConverter))]
+{%     else -%}
     [Newtonsoft.Json.JsonConverter(typeof(DateFormatConverter))]
+{%     endif -%}
 {%   endif -%}
 {%   if property.IsDeprecated -%}
     [System.Obsolete{% if property.HasDeprecatedMessage %}({{ property.DeprecatedMessage | literal }}){% endif %}]
@@ -94,7 +117,11 @@
 {% if HasAdditionalPropertiesType -%}
     private System.Collections.Generic.IDictionary<string, {{ AdditionalPropertiesType }}> _additionalProperties = new System.Collections.Generic.Dictionary<string, {{ AdditionalPropertiesType }}>();
 
+{%       if UseSystemTextJson -%}
+    [System.Text.Json.Serialization.JsonExtensionData]
+{%       else -%}
     [Newtonsoft.Json.JsonExtensionData]
+{%       endif -%}
     public System.Collections.Generic.IDictionary<string, {{ AdditionalPropertiesType }}> AdditionalProperties
     {
         get { return _additionalProperties; }

src/NJsonSchema.CodeGeneration.CSharp/Templates/DateFormatConverter.liquid

@@ -1,8 +1,23 @@
 [System.CodeDom.Compiler.GeneratedCode("NJsonSchema", "{{ ToolchainVersion }}")]
+{% if UseSystemTextJson -%}
+internal class DateFormatConverter : JsonConverter<DateTime>
+{
+    public override System.DateTime Read(ref System.Text.Json.Utf8JsonReader reader, System.Type typeToConvert, System.Text.Json.JsonSerializerOptions options)
+    {
+        return DateTime.Parse(reader.GetString());
+    }
+
+    public override void Write(System.Text.Json.Utf8JsonReader writer, System.DateTime value, System.Text.Json.JsonSerializerOptions options)
+    {
+        writer.WriteStringValue(value.ToString("yyyy-MM-dd"));
+    }
+}
+{% else -%}
 internal class DateFormatConverter : Newtonsoft.Json.Converters.IsoDateTimeConverter
 {
     public DateFormatConverter()
     {
         DateTimeFormat = "yyyy-MM-dd";
     }
-}
+}
+{% endif -%}

src/NJsonSchema.CodeGeneration.CSharp/Templates/JsonInheritanceAttribute.liquid

@@ -1,5 +1,5 @@
 [System.CodeDom.Compiler.GeneratedCode("NJsonSchema", "{{ ToolchainVersion }}")]
-[System.AttributeUsage(System.AttributeTargets.Class, AllowMultiple = true)]
+[System.AttributeUsage(System.AttributeTargets.Class | System.AttributeTargets.Interface, AllowMultiple = true)]
 internal class JsonInheritanceAttribute : System.Attribute
 {
     public JsonInheritanceAttribute(string key, System.Type type)

src/NJsonSchema.CodeGeneration.CSharp/Templates/JsonInheritanceConverter.liquid

@@ -1,4 +1,120 @@
 [System.CodeDom.Compiler.GeneratedCode("NJsonSchema", "{{ ToolchainVersion }}")]
+{% if UseSystemTextJson -%}
+internal class JsonInheritanceConverterAttribute : JsonConverterAttribute
+{
+    public string DiscriminatorName { get; }
+
+    public JsonInheritanceConverterAttribute(System.Type baseType, string discriminatorName = "discriminator")
+        : base(typeof(JsonInheritanceConverter<>).MakeGenericType(baseType))
+    {
+        DiscriminatorName = discriminatorName;
+    }
+}
+
+internal class JsonInheritanceConverter<TBase> : System.Text.Json.Serialization.JsonConverter<TBase>
+{
+    private readonly string _discriminatorName;
+
+    public JsonInheritanceConverter()
+    {
+        var attribute = System.Reflection.CustomAttributeExtensions.GetCustomAttribute<JsonInheritanceConverterAttribute>(typeof(TBase));
+        _discriminatorName = attribute?.DiscriminatorName ?? "discriminator";
+    }
+
+    public JsonInheritanceConverter(string discriminatorName)
+    {
+        _discriminatorName = discriminatorName;
+    }
+
+    public virtual string DiscriminatorName => _discriminatorName;
+
+    public override TBase Read(ref System.Text.Json.Utf8JsonReader reader, System.Type typeToConvert, System.Text.Json.JsonSerializerOptions options)
+    {
+        var document = System.Text.Json.JsonDocument.ParseValue(ref reader);
+        var hasDiscriminator = document.RootElement.TryGetProperty(_discriminatorName, out var discriminator);
+        var subtype = GetDiscriminatorType(document.RootElement, typeToConvert, hasDiscriminator ? discriminator.GetString() : null);
+
+        var bufferWriter = new System.IO.MemoryStream();
+        using (var writer = new System.Text.Json.Utf8JsonWriter(bufferWriter))
+        {
+            document.RootElement.WriteTo(writer);
+        }
+
+        return (TBase)System.Text.Json.JsonSerializer.Deserialize(bufferWriter.ToArray(), subtype, options);
+    }
+
+    public override void Write(System.Text.Json.Utf8JsonWriter writer, TBase value, System.Text.Json.JsonSerializerOptions options)
+    {
+        writer.WriteStartObject();
+        writer.WriteString(_discriminatorName, GetDiscriminatorValue(value.GetType()));
+
+        var bytes = System.Text.Json.JsonSerializer.SerializeToUtf8Bytes((object)value, options);
+        var document = System.Text.Json.JsonDocument.Parse(bytes);
+        foreach (var property in document.RootElement.EnumerateObject())
+        {
+            property.WriteTo(writer);
+        }
+
+        writer.WriteEndObject();
+    }
+
+    public virtual string GetDiscriminatorValue(System.Type type)
+    {
+        var jsonInheritanceAttributeDiscriminator = GetSubtypeDiscriminator(type);
+        if (jsonInheritanceAttributeDiscriminator != null)
+        {
+            return jsonInheritanceAttributeDiscriminator;
+        }
+
+        return type.Name;
+    }
+
+    protected virtual System.Type GetDiscriminatorType(System.Text.Json.JsonElement jObject, System.Type objectType, string discriminatorValue)
+    {
+        var jsonInheritanceAttributeSubtype = GetObjectSubtype(objectType, discriminatorValue);
+        if (jsonInheritanceAttributeSubtype != null)
+        {
+            return jsonInheritanceAttributeSubtype;
+        }
+
+        if (objectType.Name == discriminatorValue)
+        {
+            return objectType;
+        }
+
+        var typeName = objectType.Namespace + "." + discriminatorValue;
+        var subtype = System.Reflection.IntrospectionExtensions.GetTypeInfo(objectType).Assembly.GetType(typeName);
+        if (subtype != null)
+        {
+            return subtype;
+        }
+
+        throw new System.InvalidOperationException("Could not find subtype of '" + objectType.Name + "' with discriminator '" + discriminatorValue + "'.");
+    }
+
+    private System.Type GetObjectSubtype(System.Type objectType, string discriminator)
+    {
+        foreach (var attribute in System.Reflection.CustomAttributeExtensions.GetCustomAttributes<JsonInheritanceAttribute>(System.Reflection.IntrospectionExtensions.GetTypeInfo(objectType), true))
+        {
+            if (attribute.Key == discriminator)
+                return attribute.Type;
+        }
+
+        return objectType;
+    }
+
+    private string GetSubtypeDiscriminator(System.Type objectType)
+    {
+        foreach (var attribute in System.Reflection.CustomAttributeExtensions.GetCustomAttributes<JsonInheritanceAttribute>(System.Reflection.IntrospectionExtensions.GetTypeInfo(objectType), true))
+        {
+            if (attribute.Type == objectType)
+                return attribute.Key;
+        }
+
+        return objectType.Name;
+    }
+}
+{% else -%}
 internal class JsonInheritanceConverter : Newtonsoft.Json.JsonConverter
 {
     internal static readonly string DefaultDiscriminatorName = "discriminator";
@@ -117,3 +233,4 @@ internal class JsonInheritanceConverter : Newtonsoft.Json.JsonConverter
         return objectType.Name;
     }
 }
+{% endif -%}

src/NJsonSchema.CodeGeneration/NJsonSchema.CodeGeneration.csproj

@@ -22,7 +22,7 @@
     <WarningsAsErrors />
   </PropertyGroup>
   <ItemGroup>
-    <PackageReference Include="DotLiquid" Version="2.0.314" />
+    <PackageReference Include="DotLiquid" Version="2.0.385" />
     <PackageReference Include="Newtonsoft.Json" Version="9.0.1" />
   </ItemGroup>
   <ItemGroup Condition="'$(TargetFramework)' == 'netstandard1.3'">

src/NJsonSchema.Tests/Generation/InheritanceTests.cs

@@ -83,8 +83,6 @@ public async Task When_allOf_schema_is_object_type_then_it_is_an_inherited_schem
         [Fact]
         public async Task When_generating_type_with_inheritance_then_allOf_has_one_item()
         {
-            //// Arrange
-
             //// Act
             var schema = JsonSchema.FromType<Teacher>();
 
@@ -410,5 +408,36 @@ public async Task When_class_with_discriminator_has_base_class_then_mapping_is_p
             Assert.NotNull(exceptionBase.ActualTypeSchema.DiscriminatorObject);
             Assert.True(exceptionBase.ActualTypeSchema.DiscriminatorObject.Mapping.ContainsKey("MyException"));
         }
+
+        public class Apple : Fruit
+        {
+            public string Foo { get; set; }
+        }
+
+        public class Orange : Fruit
+        {
+            public string Bar { get; set; }
+        }
+
+        [JsonInheritance("a", typeof(Apple))]
+        [JsonInheritance("o", typeof(Orange))]
+        [JsonConverter(typeof(JsonInheritanceConverter), "k")]
+        public class Fruit
+        {
+            public string Baz { get; set; }
+        }
+
+        [Fact]
+        public async Task When_using_JsonInheritanceAttribute_then_schema_is_correct()
+        {
+            //// Act
+            var schema = JsonSchema.FromType<Fruit>();
+            var data = schema.ToJson();
+
+            //// Assert
+            Assert.NotNull(data);
+            Assert.Contains(@"""a"": """, data);
+            Assert.Contains(@"""o"": """, data);
+        }
     }
 }