[Java] Generator produces a dedicated field for the discriminator

[marcelstoer]

Origin: https://stackoverflow.com/q/50163882/131929

Is it correct that the generator produces a dedicated field for the discriminator?

@JsonTypeInfo(use = JsonTypeInfo.Id.NAME, include = JsonTypeInfo.As.PROPERTY, property = "errorType", visible = true)
@JsonSubTypes({
    @JsonSubTypes.Type(value = SpecificError.class, name = "SpecificError"),
})
public class GeneralError {
    @JsonProperty("errorType")
    private String errorType = null;
    ...

errorType is the declared discriminator.

When Jackson serializes a SpecificError object it includes errorType twice:

{"errorType":"SpecificError","message":"message","errorType":null}

[marcelstoer]

At FasterXML/jackson-databind#2022 the Jackson team concluded that they can't easily fix this on their end. What would help is to add a @JsonInclude(JsonInclude.Include.NON_NULL) at https://github.com/swagger-api/swagger-codegen/blob/master/modules/swagger-codegen/src/main/resources/JavaSpring/pojo.mustache#L28 for all discriminator properties.

@wing328 what is your take on this? Could this even be handled in the template directly or would the generator have to get some extra logic for that?

[VadimKirilchuk]

@marcelstoer do you really need to have this property in your class? If you don't have one, there is no need in it, it can be solved by visible = "false". So, shouldn't the question be rephrased to "why swagger uses visible = true"?