My favorites F# JSON options

This post describes my favorites F# JSON options.

Install nuget package

dotnet add package FSharp.SystemTextJson

The options

open System.Text.Json.Serialization
let options =
    JsonFSharpOptions.Default()
        .WithSkippableOptionFields(SkippableOptionFields.Always, deserializeNullAsNone = true)
        .WithAllowNullFields()
        .WithUnionExternalTag()
        .WithUnionUnwrapSingleFieldCases()
        .WithUnionUnwrapFieldlessTags()
        .ToJsonSerializerOptions()

open System.Text.Json
let serialize x = JsonSerializer.Serialize(x, options)
let deserialize (str: string) = JsonSerializer.Deserialize(str, options)

Explanation

• WithSkippableOptionFields(SkippableOptionFields.Always, deserializeNullAsNone = true) — Omitted fields or null fields will be deserialized as None. None values will be serialized as omitted.
• WithAllowNullFields() — Without this option, deserializing a null field will throw exception unless its type is Option. With this option, if the value of a field is null then:
  • If its type is nullable (string, class…), it will be deserialized as null.
  • Otherwise, an exception will be thrown.
• WithUnionExternalTag() — Encode unions as a 1-valued object: The field name is the union tag, and the value is the union fields.
• WithUnionUnwrapSingleFieldCases() — If set, the field of a single-field union case is encoded as just the value rather than a single-value array or object.
• WithUnionUnwrapFieldlessTags() — If set, union cases that don’t have fields are encoded as a bare string.

More here.