Adding an alias to the @JsonTypeInfo property lookup

[MaxwellBo]

Hi!

My org has two JSON encoding schemes active in the system, one with minified keys and values and another one with unminified keys and values. These encodings are serialized and deserialized by independent class definitions. I am unifiying these classes, by adapting existing unminified-deserializing classes to decode both encoding schemes simultaneously, and deleting minified-deserializing classes.

I have been well served by the @JsonAliass annotation, by adding @JsonAlias("<MINIFIED KEY>") to fields. However, I have run into issues when trying to adapt classes that use @JsonTypeInfo.

I would like to add A? as an alias to @JsonTypeInfo's discriminator property lookup such that the following JSON strings are deserialised by the Shape abstract class:

{ "type": "square", "width": 1.0 } AND { "A?": "A", "A": 1.0 }

Codifying this into a test:

package example;

import static org.assertj.core.api.Assertions.assertThat;

import com.fasterxml.jackson.annotation.JsonAlias;
import com.fasterxml.jackson.annotation.JsonProperty;
import com.fasterxml.jackson.annotation.JsonSubTypes;
import com.fasterxml.jackson.annotation.JsonTypeInfo;
import com.fasterxml.jackson.annotation.JsonTypeInfo.As;
import com.fasterxml.jackson.annotation.JsonTypeInfo.Id;
import com.fasterxml.jackson.databind.ObjectMapper;
import org.junit.Test;

public class DiscriminatorAliasTest {

  @JsonTypeInfo(use = Id.NAME, include = As.PROPERTY, property = "type", propertyAlias = "A?")
  @JsonSubTypes({
      @JsonSubTypes.Type(value = Square.class, names = { "square", "A" }),
      @JsonSubTypes.Type(value = Circle.class, names = { "circle", "B" })
  })
  static abstract class Shape {
    abstract public String name();
  }

  static class Square extends Shape {
    @JsonProperty("width")
    @JsonAlias("A")
    public float width;

    @Override
    public String name() { return "square"; }
  }

  static class Circle extends Shape {
    @JsonProperty("diameter")
    @JsonAlias("B")
    public float diameter;

    @Override
    public String name() { return "circle"; }
  }

  @Test
  public void testDiscriminator() throws Exception {
    ObjectMapper mapper = new ObjectMapper();

    // Passes
    String squareJsonUnminified = "{\"type\":\"square\", \"width\": 1.0 }";
    Shape square = mapper.readerFor(Shape.class).readValue(squareJsonUnminified);
    assertThat(square.name()).isEqualTo("square");

    // This fails (as expected)
    String squareJsonMinified = "{\"A?\":\"A\", \"A\": 1.0 }";
    Shape squareAgain = mapper.readerFor(Shape.class).readValue(squareJsonMinified);
    assertThat(squareAgain.name()).isEqualTo("square");
  }
}

I've used the non-existent propertyAlias parameter in this example above, so obviously this does not pass at the moment.

I'm wondering if there's a simple enough work around here using a semi-custom @JsonTypeInfo configuration and some subtle modifications to Square and Circle. I've managed to get the above test case passing with a custom @JsonDeserialize(using = ShapeDeserializer.class) but it's not a pretty or scalable solution. As you can imagine, I'm trying to make this change to many classes, so the smaller the diff the better.

Thank-you in advance to all contributors and maintainers of this library.

[cowtowncoder]

Ok, I can see how this could be useful, but knowing how the implementation works, I must say that it is unlikely that alias support will be added for Type discriminator property.

I suspect various work-arounds may exist; for example, reading of content first as JsonNode, replacing "A?" with "type".
But nothing obvious, nice and clean comes to mind unfortunately.

[MaxwellBo]

Ah thank-you for the swift response @cowtowncoder.

Your answer is somewhat a relief: I came to a similar conclusion and implemented the JsonNode workaround in my custom @JsonDeserialize(using = ShapeDeserializer.class).

Thank-you again!