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JsonInheritanceConverter.cs
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JsonInheritanceConverter.cs
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//-----------------------------------------------------------------------
// <copyright file="JsonInheritanceConverter.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>
//-----------------------------------------------------------------------
using System;
using System.Collections.Generic;
using System.IO;
using System.Linq;
using System.Reflection;
using System.Text.Json;
using System.Text.Json.Serialization;
namespace NJsonSchema.Converters
{
/// <summary>
/// The JSON inheritance converter attribute.
/// </summary>
public class JsonInheritanceConverterAttribute : JsonConverterAttribute
{
/// <summary>Gets the default discriminator name.</summary>
public static string DefaultDiscriminatorName { get; } = "discriminator";
/// <summary>
/// Gets the discriminator name.
/// </summary>
public string DiscriminatorName { get; }
/// <summary>Initializes a new instance of the <see cref="JsonInheritanceConverterAttribute"/> class.</summary>
/// <param name="baseType">The base type.</param>
/// <param name="discriminatorName">The discriminator name.</param>
public JsonInheritanceConverterAttribute(Type baseType, string discriminatorName = "discriminator")
: base(typeof(JsonInheritanceConverter<>).MakeGenericType(baseType))
{
DiscriminatorName = discriminatorName;
}
}
/// <summary>Defines the class as inheritance base class and adds a discriminator property to the serialized object.</summary>
public class JsonInheritanceConverter<TBase> : JsonConverter<TBase?>
{
/// <summary>Gets the list of additional known types.</summary>
#pragma warning disable CA1000
public static IDictionary<string, Type> AdditionalKnownTypes { get; } = new Dictionary<string, Type>();
#pragma warning restore CA1000
private readonly string _discriminatorName;
/// <summary>Initializes a new instance of the <see cref="JsonInheritanceConverter{TBase}"/> class.</summary>
public JsonInheritanceConverter()
{
var attribute = typeof(TBase).GetCustomAttribute<JsonInheritanceConverterAttribute>();
_discriminatorName = attribute?.DiscriminatorName ?? "discriminator";
}
/// <summary>Initializes a new instance of the <see cref="JsonInheritanceConverter{TBase}"/> class.</summary>
/// <param name="discriminatorName">The discriminator name.</param>
public JsonInheritanceConverter(string discriminatorName)
{
_discriminatorName = discriminatorName;
}
/// <summary>Gets the discriminator property name.</summary>
public virtual string DiscriminatorName => _discriminatorName;
/// <inheritdoc />
public override TBase? Read(ref Utf8JsonReader reader, Type typeToConvert, JsonSerializerOptions options)
{
var document = 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 MemoryStream();
using (var writer = new Utf8JsonWriter(bufferWriter))
{
document.RootElement.WriteTo(writer);
}
return (TBase?)JsonSerializer.Deserialize(bufferWriter.ToArray(), subtype, options)!;
}
/// <inheritdoc />
public override void Write(Utf8JsonWriter writer, TBase? value, JsonSerializerOptions options)
{
if (value is not null)
{
writer.WriteStartObject();
writer.WriteString(_discriminatorName, GetDiscriminatorValue(value.GetType()));
var bytes = JsonSerializer.SerializeToUtf8Bytes((object)value, options);
var document = JsonDocument.Parse(bytes);
foreach (var property in document.RootElement.EnumerateObject())
{
property.WriteTo(writer);
}
writer.WriteEndObject();
}
else
{
writer.WriteNullValue();
}
}
/// <summary>Gets the discriminator value for the given type.</summary>
/// <param name="type">The object type.</param>
/// <returns>The discriminator value.</returns>
public virtual string GetDiscriminatorValue(Type type)
{
var knownType = AdditionalKnownTypes.SingleOrDefault(p => p.Value == type);
if (knownType.Key != null)
{
return knownType.Key;
}
var jsonInheritanceAttributeDiscriminator = GetSubtypeDiscriminator(type);
if (jsonInheritanceAttributeDiscriminator != null)
{
return jsonInheritanceAttributeDiscriminator;
}
return type.Name;
}
/// <summary>Gets the type for the given discriminator value.</summary>
/// <param name="jObject">The JSON object.</param>
/// <param name="objectType">The object (base) type.</param>
/// <param name="discriminatorValue">The discriminator value.</param>
/// <returns></returns>
protected virtual Type GetDiscriminatorType(JsonElement jObject, Type objectType, string? discriminatorValue)
{
if (discriminatorValue != null)
{
if (AdditionalKnownTypes.TryGetValue(discriminatorValue, out Type? value))
{
return value;
}
var jsonInheritanceAttributeSubtype = GetObjectSubtype(objectType, discriminatorValue);
if (jsonInheritanceAttributeSubtype != null)
{
return jsonInheritanceAttributeSubtype;
}
if (objectType.Name == discriminatorValue)
{
return objectType;
}
var knownTypeAttributesSubtype = GetSubtypeFromKnownTypeAttributes(objectType, discriminatorValue);
if (knownTypeAttributesSubtype != null)
{
return knownTypeAttributesSubtype;
}
var typeName = objectType.Namespace + "." + discriminatorValue;
var subtype = objectType.GetTypeInfo().Assembly.GetType(typeName);
if (subtype != null)
{
return subtype;
}
}
throw new InvalidOperationException("Could not find subtype of '" + objectType.Name + "' with discriminator '" + discriminatorValue + "'.");
}
private static Type? GetSubtypeFromKnownTypeAttributes(Type objectType, string discriminatorValue)
{
var type = objectType;
do
{
var knownTypeAttributes = type
.GetTypeInfo()
.GetCustomAttributes(false)
.Where(a => a.GetType().Name == "KnownTypeAttribute");
foreach (dynamic attribute in knownTypeAttributes)
{
if (attribute.Type != null && attribute.Type.Name == discriminatorValue)
{
return attribute.Type;
}
else if (attribute.MethodName != null)
{
var method = type.GetRuntimeMethod((string)attribute.MethodName, Type.EmptyTypes);
if (method != null)
{
if (method.Invoke(null, Array.Empty<object>()) is IEnumerable<Type> types)
{
foreach (var knownType in types)
{
if (knownType.Name == discriminatorValue)
{
return knownType;
}
}
}
return null;
}
}
}
type = type.GetTypeInfo().BaseType;
} while (type != null);
return null;
}
private static Type? GetObjectSubtype(Type baseType, string discriminatorValue)
{
var jsonInheritanceAttributes = baseType
.GetTypeInfo()
.GetCustomAttributes(true)
.OfType<JsonInheritanceAttribute>();
return jsonInheritanceAttributes.SingleOrDefault(a => a.Key == discriminatorValue)?.Type;
}
private static string? GetSubtypeDiscriminator(Type objectType)
{
var jsonInheritanceAttributes = objectType
.GetTypeInfo()
.GetCustomAttributes(true)
.OfType<JsonInheritanceAttribute>();
return jsonInheritanceAttributes.SingleOrDefault(a => a.Type == objectType)?.Key;
}
}
}