Hi Tatu,
On Tuesday, August 13, 2019 at 12:46:33 AM UTC-3, Tatu Saloranta wrote:
>
> On Mon, Aug 12, 2019 at 5:56 PM Pablo Pazos <[email protected]
> <javascript:>> wrote:
> >
> > Hi,
> >
> > I have a model where some class attributes are concrete/final and other
> are generic, I want to avoid adding the @type to the concrete/final. Here
> is an example:
> >
> > class Action {
> >
> > DvTime time;
> > }
> >
> > class Element {
> >
> > Object value;
> > }
> >
> > final class DvTime {
> >
> > ...
> > }
> >
> > We could do:
> >
> > Element e = new Element();
> > e.setValue(new DvTime(...));
> >
> > Action a = new Action();
> > a.setTime(new DvTime(...));
> >
> >
> > When those objects are serialized, I need:
> >
> > {
> > @type: Element,
> > value: {
> > @type: DvTime,
> > ...
> > }
> > }
> >
> > {
> > @type: Action,
> > time: {
> > ...
> > }
> > }
> >
> > That avoids adding the @type = DvTime for action.time because by the
> model I know that always be a DvTime.
> >
> > Is that possible? Thanks!
>
> I think the example is missing information to fully understand
> relationship between types,
IMO all the info is there, but I have a much complex model. On the example:
Action has one DvTime
Element has one Object (this is really a DvTime superclass, I set object to
avoid adding another class to the model*)
* this really would be
abstract class Dv {
}
class DvTime extends Dv {
Date value
... other fields here
}
Then:
class Element {
Dv value
}
but in general, polymorphic type handling
> is optional and only used for classes with `@JsonTypeInfo` in base
> class, or annotation on property. So you can select which type
> hierarchies will use type ids.
>
I'm very new to Jackson and don't know what JsonTypeInfo is for :(
But related to the hierarchies to use, in Action.time there shouldn't be
any hierarchies. And in Element.value the whole Dv hierarchy is allowed.
That is why on Action.time I don't need the @type and yes on Element.value.
>
> Second thing is that for deserialization, one can omit "type id" if
> (but only if!) there is property `defaultImpl` for `@JsonTypeInfo`. So
> that could be pointing to final implementation.
>
That happens on Action.time, but not sure how that is linked to
JsonTypeInfo or to defaultImpl, I'm lacking experience in Jackson, sorry.
> There is no matching setting (yet) to prevent outputting of type id
> when polymorphic types are enabled. There is an issue to support it,
> and maybe it gets eventually implemented.
>
I guess that is needed for what I need to do here. The issue I have is 1.
the model is big and complex, 2. most of the relationships are final (don't
really need the @type and cutting those would cut some bytes from the final
JSON), 3. only few relationships (fields) are polymorphic, but on those I
could have a lot of options in terms of the inheritance hierarchy.
>
> Those are the existing mechanisms for selective use of type ids. But
> in general types are not meant to use mix-and-match approach as that
> is very difficult to support on deserialization side.
>
In my case I think that is easy to do by looking/inspecting (with
reflection) the model, but not sure how Jackson does that internally, I
guess an annotation could help there to know which fields are final, but I
think that could be done with normal java reflection without any
annotations. Maybe I'm wrong :)
>
> -+ Tatu +-
>
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