raboof/pekko
1
0
Fork 0
Code Issues Pull requests Projects Releases 6 Packages Wiki Activity Actions 10

Document workaround for jackson serialiaztion of scala case objects (#29531)

Browse source 
* workaround for jackson serialiaztion of scala case objects

* improved sentence
This commit is contained in:
Renato Cavalcanti 2020-09-02 14:19:13 +02:00 • committed by GitHub
parent 192be028a0
commit 32ec0428d3
No known key found for this signature in database
GPG key ID: 4AEE18F83AFDEB23
2 changed files with 71 additions and 15 deletions
Download patch file Download diff file Expand all files Collapse all files

13
akka-docs/src/main/paradox/serialization-jackson.md
View file

@ -164,11 +164,20 @@ when using polymorphic types.
### ADT with trait and case object
In Scala it's common to use a sealed trait and case objects to represent enums. If the values are case classes
It's common in Scala to use a sealed trait and case objects to represent enums. If the values are case classes
the `@JsonSubTypes` annotation as described above works, but if the values are case objects it will not.
The annotation requires a `Class` and there is no way to define that in an annotation for a `case object`.
This can be solved by implementing a custom serialization for the enums. Annotate the `trait` with
The easiest workaround is to define the case objects as case class without any field.
Alternatively, you can define an intermediate trait for the case object and a custom deserializer for it. The example below builds on the previous `Animal` sample by adding a fictitious, single instance, new animal, an `Unicorn`.
Scala
: @@snip [SerializationDocSpec.scala](/akka-serialization-jackson/src/test/scala/doc/akka/serialization/jackson/SerializationDocSpec.scala) { #polymorphism-case-object }
The case object `Unicorn` can't be used in a `@JsonSubTypes` annotation, but its trait can. When serializing the case object we need to know which type tag to use, hence the `@JsonTypeName` annotation on the object. When deserializing, Jackson will only know about the trait variant therefore we need a custom deserializer that returns the case object.
On the other hand, if the ADT only has case objects, you can solve it by implementing a custom serialization for the enums. Annotate the `trait` with
`@JsonSerialize` and `@JsonDeserialize` and implement the serialization with `StdSerializer` and
`StdDeserializer`.