Start Debugging

Tag: system-text-json

14 posts · Page 1 of 2

2026-08-10 csharp dotnet dotnet-11

How to customize source-generated System.Text.Json serialization with a type-info resolver modifier

Attach a JsonTypeInfo modifier to a source-generated JsonSerializerContext in .NET 11: why new MyContext(options) silently drops it, the WithAddedModifier setup that works, the fast path you give up (measured), and the naming-policy trap that makes modifiers no-op.

2026-07-29 errors csharp dotnet

Fix: Reflection-based serialization has been disabled for this application

This InvalidOperationException means PublishTrimmed or PublishAot flipped JsonSerializerIsReflectionEnabledByDefault to false. Fix it with a source-generated JsonSerializerContext.

2026-07-27 csharp dotnet dotnet-11

How to serialize a polymorphic type hierarchy with JsonDerivedType in System.Text.Json

A complete guide to polymorphic JSON in .NET 11: JsonDerivedType and JsonPolymorphic, why the declared type decides everything, the $type ordering rule, every exception the feature throws, the contract model for types you do not own, and what ASP.NET Core emits in OpenAPI.

2026-07-21 csharp dotnet-11 system-text-json

System.Text.Json Learns to Serialize C# Union Types in .NET 11 Preview 6

How System.Text.Json in .NET 11 Preview 6 serializes the new C# union types by writing the active case, and the JsonUnionAttribute and type-classifier APIs that handle ambiguous cases.

2026-06-10 dotnet-11 csharp system-text-json

System.Text.Json Finally Writes JSON Lines in .NET 11 Preview 5

.NET 11 Preview 5 adds JsonSerializer.SerializeAsyncEnumerable with topLevelValues: true, so System.Text.Json can now stream JSONL out, not just read it.

2026-05-30 migration newtonsoft-json system-text-json

Migrate from Newtonsoft.Json 13 to System.Text.Json in a large .NET 11 codebase

A version-pinned playbook for swapping Newtonsoft.Json 13.0.4 for the in-box System.Text.Json on .NET 11: the attribute and settings mappings, the defaults that silently change your wire format, a staged rollout strategy, verification, and the gotchas that bite large codebases.

2026-05-22 comparison system-text-json newtonsoft-json

System.Text.Json vs Newtonsoft.Json in 2026: which should you pick?

Pick System.Text.Json for new .NET 11 code: it ships in-box, is roughly 2x faster, and is the only one that works with Native AOT. Reach for Newtonsoft.Json only for JSONPath, TypeNameHandling, or genuinely lenient JSON.

2026-05-14 errors csharp dotnet

Fix: A possible object cycle was detected

System.Text.Json refuses to serialize graphs with back-references. Set ReferenceHandler.IgnoreCycles, project to a DTO, or mark the back-pointer with [JsonIgnore]. Preserve is a last resort.

2026-05-13 errors csharp dotnet

Fix: System.Text.Json.JsonException: The JSON value could not be converted

System.Text.Json throws this when the incoming JSON token doesn't match the CLR target type. Match the JSON to the type, or register a JsonConverter or JsonSerializerOption that bridges them.

2026-05-08 errors csharp dotnet

Fix: The JSON value could not be converted to System.DateTime

System.Text.Json only accepts ISO 8601 strings for DateTime. Send 2026-05-08T14:00:00Z or register a JsonConverter that parses your format. Empty strings and Unix timestamps both throw.