On Mon, Aug 12, 2019 at 10:54 PM Pablo Pazos <pablo....@gmail.com> wrote:
>
> 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 <pabl...@gmail.com> 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 :(
It is annotation used to enable Polymorphic Type handling; explained f.ex here:
https://www.baeldung.com/jackson-inheritance
>
> 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.
Saving some bytes may be nice thing to have, but in case of type id
handling tends to
1. Cause massive complexity in handling code if it tries to figure
when, how and why type id might be missing
2. Lead to unexpected, hard to diagnose failures due to complexity.
Given this, Jackson really does not try to be clever and omit (or
ignore) type information:
generally a property either HAS to have (and does use) type ids, or
does not use or have those. There is that one little exception to
support edge cases wherein even if Type Id is expected, it MAY be
omitted if (and only if) a default implementation is defined
(`defaultImpl` property of `@JsonTypeInfo`)
-+ Tatu +-
--
You received this message because you are subscribed to the Google Groups
"jackson-user" group.
To unsubscribe from this group and stop receiving emails from it, send an email
to jackson-user+unsubscr...@googlegroups.com.
To view this discussion on the web visit
https://groups.google.com/d/msgid/jackson-user/CAL4a10g_53Qqk0iELtNZgbdrUcRET2X4Gs6%2B7nCh6oE-oSs4SQ%40mail.gmail.com.
