I am happy to announce FSharp.SystemTextJson version 1.1!

FSharp.SystemTextJson is a library that provides support for F# types in .NET's standard System.Text.Json.

Here is a summary of the new features in v1.0.

Fluent configuration

The library now comes with a new syntax for configuration. Instead of a constructor with a mix of optional arguments and enum flags, you can now use a more consistent fluent syntax.

  • The baseline options are declared using one of these static methods on the JsonFSharpOptions type: Default(), NewtonsoftLike(), ThothLike() or FSharpLuLike().
  • Then, fluent instance methods set various options and return a new instance of JsonFSharpOptions.
  • Finally, a converter with the given options can be either added to an existing JsonSerializerOptions with the method AddToJsonSerializerOptions(), or to a new one with ToJsonSerializerOptions().

For example:

let options =

type SomeUnion =
    | SomeUnionCase of x: int * y: string

JsonSerializer.Serialize(SomeUnionCase (1, "test"), options)
// --> {"type":"SomeUnionCase","x":1,"y":"test"}

Note that in the future, newly added options will be available via the fluent configuration, but they may not always be added to the constructor syntax; especially because this can break binary compatibility (see this issue).

Skippable option fields

In version 1.0, the default behavior for fields of type option and voption changed: they are no longer serialized as a present or missing field, and instead as a null field.

While the pre-1.0 behavior can be recovered by using the JsonSerializerOptions property DefaultIgnoreCondition, this has other side-effects and multiple users have asked for a cleaner way to use options for missing fields.

This is now possible with the option SkippableOptionFields. This is the first option that is only available via fluent configuration, and not as a JsonFSharpConverter constructor argument.

let options =

JsonSerializer.Serialize({| x = Some 42; y = None |}, options)
// --> {"x":42}

Happy coding!

By Loïc "Tarmil" Denuzière on Saturday, January 21, 2023

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