Issue Setting JsonNullable Field with Instancio Generator

[RuslanNyko]

Hello,
I’m encountering an issue while using Instancio to generate instances of a class that contains a JsonNullable field. Below is my setup:

Pojo Class:

public class Pojo {
    private JsonNullable<String> string;

    public JsonNullable<String> getString() {
        return string;
    }

    public void setString(JsonNullable<String> string) {
        this.string = string;
    }
}

Instancio Generator Code:

Pojo pojo = Instancio.of(Pojo.class)
    .generate(Select.field(Pojo::getString), g -> g.oneOf("S", "P", "O"))
    .create();

Exception Thrown:

Can not set org.openapitools.jackson.nullable.JsonNullable field com.dto.Pojo.string to java.lang.String
    at java.base/jdk.internal.reflect.FieldAccessorImpl.throwSetIllegalArgumentException(FieldAccessorImpl.java:228)
    at java.base/jdk.internal.reflect.FieldAccessorImpl.throwSetIllegalArgumentException(FieldAccessorImpl.java:232)
    at java.base/jdk.internal.reflect.MethodHandleObjectFieldAccessorImpl.set(MethodHandleObjectFieldAccessorImpl.java:115)

Question:

How can I correctly use Instancio to generate and set values for a JsonNullable<String> field? Is it possible to utilize InstancioServiceProvider for this purpose, or is there another recommended approach?

Any guidance or examples on handling JsonNullable with Instancio would be greatly appreciated!

[armandino]

Hi @RuslanNyko,

You can achieve this using a Scope:

Scope jsonNullableScope = Select.scope(Pojo::getString);

Pojo pojo = Instancio.of(Pojo.class)
    .generate(Select.allStrings().within(jsonNullableScope), g -> g.oneOf("S", "P", "O"))
    .create();

You could also use InstancioServiceProvider if you don't want to specify these values manually each time you create your POJO.

Please see these links for more details:

• https://www.instancio.org/user-guide/#selector-scopes
• https://github.com/orgs/instancio/discussions/593

[RuslanNyko]

Thanks for the answer, I need a general solution that supports many types. Is it possible to put this in a separate class, for example, which implements InstancioServiceProvider?

[armandino]

Yes, it should be possible to add a generator for JsonNullable in a InstancioServiceProvider implementation.

I'm not sure what you mean by a general solution since in the example, the expected values are strings "S", "P", "O". Can you provide additional examples?

[RuslanNyko]

I have two classes, Pojo and Pojo2, where some fields are of type JsonNullable. I want to know if it is possible to check if a generator has already been defined for a particular field and reuse it in an instance generation, such as with the Instancio library.

Here are the two classes:

class Pojo {
  private JsonNullable<String> stringJsonNullable;
  private JsonNullable<Integer> integerJsonNullable;
  private JsonNullable<Long> longJsonNullable;
  private JsonNullable<BigDecimal> bigDecimalJsonNullable;
  private JsonNullable<List<String>> listJsonNullable;
}

class Pojo2 {
  private JsonNullable<String> stringJsonNullable;
  private JsonNullable<List<Pojo>> listJsonNullable;
}

I am using the following code to generate instances of Pojo2:

private Pojo2 generatePojo2(){
    return Instancio.of(Pojo2.class)
        .generate(Select.field("stringJsonNullable"), g -> g.text().pattern("#d#d#d"))
        .create();
}

In this example, a String will be generated for the stringJsonNullable field. However, since the field is of type JsonNullable<String>, I want to ensure that the generated value is wrapped in JsonNullable—i.e., the generated string should be JsonNullable.of("value"), not just a plain string.

The Question:

• Is it possible to customize the generator to automatically wrap the generated value in JsonNullable?

• Can I check if a generator has already been applied to a specific field (e.g., stringJsonNullable) and reuse it for fields of type JsonNullable?

[armandino]

• Is it possible to customize the generator to automatically wrap the generated value in JsonNullable?

There's no feature that allows wrapping generated values automatically. Instead you will need to target strings within JsonNullable using selectors and scopes using Select.allStrings().within(scope(Pojo::getStringJsonNullable)).

Alternatively, you can define a JsonNullable generator or Supplier. You can find an example in this post.

• Can I check if a generator has already been applied to a specific field (e.g., stringJsonNullable) and reuse it for fields of type JsonNullable?

It's not possible to check if a generator has been defined for a specific field. If you want a JsonNullable generator to be applied automatically, then you could use the InstancioServiceProvider. You can still override specific fields as needed.

[RuslanNyko]

Thanks for the answer, I will try to use the scope