Query on JsonTypeInfo.defaultImpl

[Paulomi Mukherjee]

Parent.java has

 

@JsonTypeInfo(

        use = JsonTypeInfo.Id.NAME,

        defaultImpl = com.common.model.Parent.class,

        include = JsonTypeInfo.As.EXISTING_PROPERTY,

        property = "@class"

)

@JsonSubTypes({

        @JsonSubTypes.Type(value = com.common.model.Child.class, name = "com.common.model.Child"),

        @JsonSubTypes.Type(value = com.common.model.Grandchild.class, name = "com.common.model.Grandchild")

})

 

Child.java has

 

@JsonTypeInfo(

        use = JsonTypeInfo.Id.NAME,

        defaultImpl = com.common.model.Parent.class,

        include = JsonTypeInfo.As.EXISTING_PROPERTY,

        property = "@class"

)

@JsonSubTypes(@JsonSubTypes.Type(value = com.common.model.Grandchild.class, name = "com.common.model.Grandchild"))

 

 

Note: in Child.java I mentioned defaultImpl as the Parent class as Child class is abstract. My aim is to create a parent object if @class is missing in the payload.

 

But when I try to create the child object, I get the below error:

JSON parse error: Missing type id when trying to resolve subtype of [simple type, class com.common.model.Child]: missing type id property '@class'; nested exception is com.fasterxml.jackson.databind.exc.InvalidTypeIdException: Missing type id when trying to resolve subtype of [simple type, class com.common.model.Child]: missing type id property '@class'\n at [Source: (PushbackInputStream); line: 3, column: 1]

 

I tried giving defaultImpl = Object.class in JsonTypeInfo of Child class. Still I get the same missing type id property '@class' error.

 

So, my question is, is it mandatory for defaultImpl to be on the same class and any of the children class?

Can I not give any random or the parent class in defaultImpl ?

Spring boot version is 2.1.5.

 

[Tatu Saloranta]

No --- actually it is recommended that child classes do NOT add
`@JsonTypeInfo` at all, because doing that may lead to impression that
it would be used -- and, worse, this can lead to incompatible behavior
between serialization (during which sub-class info IS used as
available from runtype value) and deserialization (during which only
base class information is usually available).

>
> Can I not give any random or the parent class in defaultImpl ?
>
> Spring boot version is 2.1.5.

No, you must use type that is compatible with expected result base type.
That is, something that is assingment-compatible: if field with
polymorphic value is declared to be a `BaseType`, default
implementation must be `BaseType` or another type that
extends/implements it.

Things get more confusing if different base type is specified during
serialization and deserialization: ideally same type would be used,
but since root value type handling is fundamentally asymmetric (when
serializing there is an instance available, with subtype class; on
deserialization base type is usually given).

-+ Tatu +-

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