Option for not setting `null` as default value for non-required fields

[jostl]

Hi. When code is generated from properties which are non-required, the default value is automatically set to null. I would like to not generate any default value for these fields. Is there a way to do this? If not, is there a possibility to add this functionality?

The practical problem for me is that when dealing with multiple models and mappers, the default value allows for making mistakes more easily when writing the mappers.

Example:

Generated code now:

data class Data(
    val otherField: String,
    val nonrequired: String? = null
)

But I would prefer:

data class Data(
    val otherField: String,
    val nonrequired: String?
)

[pwall567]

Hi, thanks for the suggestion.

The use of nullable types for non-required properties is something of a compromise, as discussed recently in Issue #17. Most JSON deserialization libraries will treat a missing value and a "null" value as equivalent, so generating a nullable reference is in most cases a practical way of handling properties that are not in the required list.

I'm not sure what you would expect a deserialization function to do when given a JSON object containing just the otherField property, to be deserialized into the Data class in your example.

I'm looking at other ways of handling optional properties, but in the meantime, I'm not convinced that your proposal would result in useful generated code (and would require a moderate amount of effort to implement).

-Peter

[gunnarkd]

Thanks for the swift response! We've had great use of your library so far

We are happy with the use of nullable types for non-required properties, the issue on our end is that we would greatly benefit from the constructors of the generated classes to have no default values.
We use json-schema as contracts between applications, and do quite a bit of mapping between internal and generated classes as a result. At this point in our development cycle we have quite frequent changes in the json-schemas.
Due to the default values, the introduction of a new non-required property does not lead to a change in the constructors that the mapping code use, and such a change can easily be missed as it does not result in any compilation errors.

I'm not sure how this would be an issue for the deserialization function, given the json

{"otherField":"some-value"}

and the class

data class Data(
    val otherField: String,
    val nonrequired: String?
)

wouldn't the deserializer use

Data(otherField = "some-value", nonrequired = null)

instead of

Data(otherField = "some-value")

?

Jackson have no problem with deserializing to data classes with no default values.

My first thought was that this could be implemented by introducing a new config to the engine, and modify the .mustache templates for classes to not include = null when disabled. But I might be missing something?