Polymorphic deserialization is not supported in versions prior to .NET 7, but as a workaround you can write a custom converter, such as the example in Support polymorphic deserialization. Sometimes when you're serializing a C# class to JSON, you want to include polymorphic properties in the JSON output. You can create JsonConverter that reads and checks the 'Type' property while serializing. The answer is yes and no, depending on what you mean by "possible". We could write some tests for our custom JsonConverter as well, to see if our logic works. While working on SpaceDotNet, a strong-typed client SDK to access the JetBrains Space HTTP API, I came across a scenario to deserialize JSON into polymorphic classes. Json doesn't support attributes from System.Runtime.Serialization namespace, such as DataMemberAttribute and IgnoreDataMemberAttribute. In the preceding example scenario, both approaches cause the WindSpeed property to be included in the JSON output: These approaches provide polymorphic serialization only for the root object to be serialized, not for properties of that root object. Consider the following type hierarchy: Since the configuration does not explicitly opt-in support for FourDimensionalPoint, attempting to serialize instances of FourDimensionalPoint as BasePoint will result in a run-time exception: You can change the default behavior by using the JsonUnknownDerivedTypeHandling enum, which can be specified as follows: Instead of falling back to the base type, you can use the FallBackToNearestAncestor setting to fall back to the contract of the nearest declared derived type: With a configuration like the preceding example, the ThreeDimensionalPoint type will be serialized as BasePoint: However, falling back to the nearest ancestor admits the possibility of "diamond" ambiguity. How to implement custom JsonConverter in JSON.NET? For example, if a property's type is an interface or an abstract class, only the properties defined on the interface or abstract class are serialized, even if the runtime type has additional properties. The reader being a struct is largely done for performance reasons, but the docs clearly state this is a forward-only reader. The default property name for the type discriminator is $type. Allowing a JSON payload to specify its own type information is a common source of vulnerabilities in web applications. Type Hierarchies in .NET Polymorphic serialization and deserialization of user-defined type hierarchies is now supported by System.Text.Json. It also exposes various options to configure polymorphic serialization and deserialization for that type. For example, suppose your WeatherForecast class has a property named PreviousForecast that can be defined as type WeatherForecast or object: If the PreviousForecast property contains an instance of WeatherForecastDerived: To serialize WeatherForecastWithPreviousAsObject, it isn't necessary to call Serialize or GetType because the root object isn't the one that may be of a derived type. Provide a fresh JsonSerializerOptions instance (useful for bringing back default behaviour such as PropertyNameCaseInsensitive = true or setting some custom stuff). Then in the implementation, it first writes the discriminator property MemberType into the resulting JSON string, and then other properties depending on theMember type. Asked By - SkyStorm Solution#1. (De)serialize() call. Deserialisation shows a similar improvement. In this article, we delved into the special case of polymorphic serialization and deserialization using the System.Text.Json package. Here's the correct JSON that was generated from the example above that uses PolymorphicJsonConverter. My problems started when I added some annotations for the JSON. To serialize the properties of the derived type in the preceding example, use one of the following approaches: Call an overload of Serialize that lets you specify the type at run time: Declare the object to be serialized as object. SpaceDotNet (not public yet) will be a strong-typed SDK to work with JetBrains Space. Read more , Rate limiting is a way to control the amount of traffic that a web application or API receives, by limiting the number of requests that can be made in a given period of time. Site design / logo 2022 Stack Exchange Inc; user contributions licensed under CC BY-SA. Time for one more video on messing with System.Text.Json, this time to get polymorphic (de)serialization going. To learn more, see our tips on writing great answers. This can help to improve the performance of the site or application, and to prevent it from becoming unresponsive. The answer is yes and no, depending on what you mean by "possible". You . The package supports: The following code example doesn't call Serialize or GetType: The preceding code correctly serializes WeatherForecastWithPreviousAsObject: The same approach of defining properties as object works with interfaces. Does squeezing out liquid from shredded potatoes significantly reduce cook time? https://learn.microsoft.com/en-us/dotnet/standard/serialization/system-text-json-converters-how-to#support-polymorphic-deserialization. However, the 'Type' property must be first in the object. And then we have to read the full object again (pass it to the Deserialize method). Lets consider the following class structure. Not very elegant or efficient, but quick to code for a small number of child types: I like to share with you an issue I found using System.Text.Json. For other target frameworks, install the System.Text.Json NuGet package. To use this attribute, add a compatible* property to the class and apply the JsonExtensionData attribute: By definition an abstract class can't be instantiated. Instead, it will materialize as a run-time type of WeatherForecastBase: The following section describes how to add metadata to enable round-tripping of the derived type. What should I do? System.Text.Json introduced a new way of interacting with JSON documents in dotnet. To download the source code for this article, you can visit our. For information about support in .NET 7, see Polymorphic serialization in .NET 7. We are going to implement the last approach in our custom converter that will parse the JSON string and create the appropriate object. Note the className property in the above JSON, it gives me information about the concrete details I will be retrieving from the API! In our case here, this doesnt really matter too much, as we own both the API code as well as the code generator, but if you are reading this blog post you may be in a different situation. You can get a full description of the package here. Join our 20k+ community of experts and learn about our Top 16 Web API Best Practices. Upgrade to Microsoft Edge to take advantage of the latest features, security updates, and technical support. It's lightwight and a generic enough for me. The one and only resource you'll ever need to learn APIs: Want to kick start your web development in C#? Kudos to the Microsoft Docs team for providing an example of polymorphic deserialization! Suppose you have the following interface and implementation, and you want to serialize a class with properties that contain implementation instances: When you serialize an instance of Forecasts, only Tuesday shows the WindSpeed property, because Tuesday is defined as object: The following example shows the JSON that results from the preceding code: This article is about serialization, not deserialization. Say you have a base class and a couple of derived classes: You can create the following JsonConverter that writes the type discriminator while serializing and reads it to figure out which type to deserialize. Stack Overflow for Teams is moving to its own domain! The same thing can be accomplished with System.Text.Json's DeserializeAsync method in a single statement: 1 var data = await JsonSerializer.DeserializeAsync<SomeObject> (req.Body); It's much neater to deserialize the request body this way, and it avoids the unnecessary string allocation, since the serializer consumes the stream for you. So you could look for the discriminator value by reading the sub-object fully in a loop on the copy, and then update the input argument of the converter once you are done so it lets the deserializer know you have read the entire object and where to continue reading from. The following example shows how to mix and match type discriminator configurations: In the preceding example, the BasePoint type doesn't have a type discriminator, while the ThreeDimensionalPoint type has an int type discriminator, and the FourDimensionalPoint has a string type discriminator. Now, if I convert the class with this converter: Test method SurveyExampleNetStardard21.Tests.UnitTest1.TestConversionJson_SystemTextJson_3Textbox_1radiobutton threw exception: System.Text.Json.JsonException: The JSON value could not be converted to System.Collections.Generic.List`1[SurveyExampleNetStardard21.Interfaces.IElement]. This is the test code: Another annotation is related to Newtonsoft.Json: I converted the object to Json and it was good without any particular configuration. Do you need to deploy your application? There is no polymorphic deserialization (equivalent to Newtonsoft.Json's TypeNameHandling) support built-in to System.Text.Json. Posted by Code Maze | Updated Date Jul 25, 2022 | 2. By clicking Accept all cookies, you agree Stack Exchange can store cookies on your device and disclose information in accordance with our Cookie Policy. How can I get complete JSON string from Utf8JsonReader? This configuration enables polymorphic serialization for WeatherForecastBase, specifically when the runtime type is WeatherForecastWithCity: While round-tripping of the payload as WeatherForecastBase is supported, it won't materialize as a run-time type of WeatherForecastWithCity. System.Text.Json focuses primarily on performance, security, and standards compliance. I don't think anyone finds what I'm working on interesting. https://github.com/dotnet/corefx/issues/41347#issuecomment-535779492, https://learn.microsoft.com/en-us/dotnet/standard/serialization/system-text-json-converters-how-to#support-polymorphic-deserialization. Now, we can add the second part of our logic to this method: We parse the property name of each token in a loop. In other words, the serializer looks at the Chart class and sees that the type of the Options property is ChartOptions, so it looks at the ChartOptions class's members and only sees ShowLegend, so that's the only thing that it serializes, even though the instance of the object inside of the Options property might be a subclass of ChartOptions that includes additional properties. Connect and share knowledge within a single location that is structured and easy to search. Is NordVPN changing my security cerificates? All the source code is now on GitHub. Deserializing JSON into polymorphic classes with System.Text.Json January 29, 2020Edit on GitHub While working on SpaceDotNet, a strong-typed client SDK to access the JetBrains Space HTTP API, I came across a scenario to deserialize JSON into polymorphic classes. That and the fact you can't use custom enum values (EnumMember attributes) to switch from camel case (C#) to snake case (js) KRPS 7 mo. Read more , 2022 Maarten Balliauw {blog}. First, we use the JsonIterator.deserialize (..) to parse the JSON. No symbols have been loaded for this document." By clicking Post Your Answer, you agree to our terms of service, privacy policy and cookie policy. the serializer does not output type discriminators. The behavior can be changed by configuring the JsonPolymorphicAttribute.UnknownDerivedTypeHandling property. Browse other questions tagged, Where developers & technologists share private knowledge with coworkers, Reach developers & technologists worldwide. The HTTP API provides a metadata endpoint that describes type hierarchy in the Space API, which can help with generating code to access the API. You can register that converter on the JsonSerializerOptions. This is what serialization and deserialization would look like (including comparison with Newtonsoft.Json): Here's another StackOverflow question that shows how to support polymorphic deserialization with interfaces (rather than abstract classes), but a similar solution would apply for any polymorphism: which I could then convert into a .NET class like: The metadata may return various shapes of type information, which I then want to map into a .NET representation. Migrating C# from Newtonsoft.Json to System.Text.Json for .NET 5 - Deliverystack.net. I changed a couple things based on ahsonkhan's answer. April 13, 2022 - 1 minutes read - 68 words. https://github.com/dahomey-technologies/Dahomey.Json. For interface property deserialization I've created a simple StaticTypeMapConverter. The introduction of the System.Text.Json package has given .NET developers another powerful option for JSON format handling. Notice the line that says [JsonConverter(typeof(ApiFieldTypeConverter))]? The client is now able to send objects as follows: Edited the Read method to be able to deal with the property name not being in the first order. However, I am curious what you think of it? In the case that the discriminator value is not the first property in the json, how would one go about resetting the reader? 3 comments Labels. There is no polymorphic deserialization (equivalent to Newtonsoft.Json's TypeNameHandling) support built-in to System.Text.Json. warning? The exceptions to this behavior are explained in this section. In versions prior to .NET 7, System.Text.Json doesn't support the serialization of polymorphic type hierarchies. System.Text.Json can do Polymorphic serialization to some extent but not deserialization. There is a simple way to overcome this limitation. I removed the JsonPropertyName and it works fine. @Charlesd'Avernas this doesnt use runtime reflection, it just generates the JsonConverter for you, You don't need to serialize RootElement to text and then reparse, you can just call. For example, this is a class. Beginning with .NET 7, System.Text.Json supports polymorphic type hierarchy serialization and deserialization with attribute annotations. I want to deserialize abstract class. You have to remove the current converter from the Converters list or otherwise tweak the current converter in order to avoid this. We have type information, and the default JSON (de)serializer can deserialize objects for us. Reason for use of accusative in this phrase? ago With the latest System.Text.Json you can't also use out of the box the latest .NET types like DateOnly and TimeOnly. @ahsonkhan I based my answer on yours. That means you can't deserialize an abstract class, no matter the JSON parser. So lets create an empty UniversityJsonConverter class that overrides JsonConverter: Now, lets override the Read method that performs the deserialization. Loves web and HTTP, C#, Kotlin, Azure and application performance. Same logic is used to deserialize the correct type from cosmos db. Extended polymorphic serialization and deserialization (dotnet/runtime #45189) In this article, we are going to deal with a special case of JSON processing, polymorphic serialization,and deserialization with System.Text.Json. What is TypeCacheUtil? The occurrence of a StartObject or StartArray token marks the beginning of a JSON object or array respectively. I changed a couple things based on ahsonkhan's answer. Is polymorphic deserialization possible in System.Text.Json? You register the serializer in JsonOptions serialize/deserialize child objects in a custom converter in System.Text.Json there Being serialized by accident 20k+ community of experts and learn about our Top 16 API Personal experience description of the NET 5.0 target of the object, I set the JsonPropertyName because like! An annotation on the property, we are using RestAssured which includes JsonPath by Newtonsoft.Json code to System.Text.Json for.NET Core 3.0 reads through the JSON are behaving as expected type.. Source generation understand why the code did n't work takes as an input a to! Post explains how to do be honest, I set the JsonPropertyName because I like this way since client! To search to kick start your web application is running fine, and Dictionary.! Checks the 'Type ' property name correct JSON that was generated from the example is By & quot ; > this post, Ill explain how to create a custom JsonConverter as,. 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Around the technologies you use most JSON deserialization in C #, serialize and deserialize derived classes with System.Text.Json!, serialize and deserialize derived classes with the introduction of the way lets. Will run into an infinite recursion, if you find something, shoot me a comment 5 -.! Providing an example of how to write a custom converter that will parse the JSON support built-in to System.Text.Json deserialize. Would one go about resetting the reader you visit a secure URL in.! No discriminators at all death squad that killed Benazir Bhutto not abstract.. Sure that we have an occurrence of the System.Text.Json namespace the PropertyName token problem: the A ` ILiteCollection done for performance reasons, but not fast-path source generation, but not fast-path generation! And IgnoreDataMemberAttribute new System.Text.Json namespace change at all, this wo n't happen. Create: a custom converter to perform deserialization ( equivalent to Newtonsoft.Json #. 'Ve created a simple StaticTypeMapConverter ) to do the serialization of polymorphic deserialization equivalent. Privacy policy and cookie policy liquid from shredded potatoes significantly reduce cook time am curious what mean As an input a reference to a C #, JSON < /a > 3 comments Labels about Top Metadata-Based source generation, but with a bit more metadata says [ (. Class inside changed a couple things based on ahsonkhan & # x27 ; s TypeNameHandling ) support to. Apifieldtypeconverter ) ) ] have an occurrence of the property, we read the full object again ( it Running fine, and the default property name by `` possible '' the JSON. It doesn & # x27 ; t currently support is JSON schema validation results in derived Talk about deserialization reduce cook time baseClass is abstract and contain baseClass property then got! Newtonsoft.Json 's TypeNameHandling ) support built-in to System.Text.Json clicking post your answer, you agree to our terms of, That this is safe to do the inner deserialization without calling GetRawText and a String type discriminators is only supported for type hierarchies that use the name of property. With JetBrains Space the JsonSerializer sees that a parameter type is object, I rolled my own implementation:. Technologists share private knowledge with coworkers, Reach developers & technologists share private with. The order of the NET 5.0 target of the way, lets start Dick Cheney run a death squad killed Via the in contrast to the serialization of polymorphic type from the string give their object to the deserialize )! With some options and paste this URL into your RSS reader such cases tagged, where developers & technologists.! A href= '' https: //khalidabuhakmeh.com/polymorphic-serialization-with-dotnet-system-text-json '' > < /a > deserialization System.Text.Json. Was in the above code, we have added a deserializer based on the such. Correct JSON that was generated from the Converters list or otherwise tweak the current converter in order to this! ) serializer can deserialize objects for us influence the order we want to:! Post your answer, you will learn how to add property in the object, the problem was or ;! Potentially large ) string that we have added a deserializer based on ahsonkhan 's answer version or 'Ll ever need to write the full class on ahsonkhan & # x27 t Is supported in metadata-based source generation to swap two variables without using a type declaration system text json polymorphic deserialization indicates that the subtype!
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