ObjectBox converter for List<String> properties in your Kotlin data model. http://objectbox.io/

Model.kt

package com.test.objectbox.models

import io.objectbox.annotation.Convert
import io.objectbox.annotation.Entity
import io.objectbox.annotation.Id

@Entity data class Article(
        @Id var id: Long = 0,
        @Convert(converter = StringListConverter::class, dbType = String::class)
        var strings: List<String>? = null,
)

ObjectBoxStringListConverter.kt

package com.test.objectbox.converters

import io.objectbox.converter.PropertyConverter

class StringListConverter : PropertyConverter<List<String>, String> {
    override fun convertToEntityProperty(databaseValue: String?): List<String> {
        if (databaseValue == null) return ArrayList()
        return databaseValue.split(",")
    }

    override fun convertToDatabaseValue(entityProperty: List<String>?): String {
        if (entityProperty == null) return ""
        if (entityProperty.isEmpty()) return ""
        val builder = StringBuilder()
        entityProperty.forEach { builder.append(it).append(",") }
        builder.deleteCharAt(builder.length - 1)
        return builder.toString()
    }
}

Was looking for something like this myself. Just a heads up to anyone else that arrived here via Google: this code has a bug if anything in the list of strings is null or contains a comma.

Here's what I use.

import org.json.JSONArray;

import java.util.ArrayList;
import java.util.List;

import io.objectbox.converter.PropertyConverter;

public class StringListConverter implements PropertyConverter<List<String>, String> {
    @Override
    public List<String> convertToEntityProperty(String databaseValue) {
        if (databaseValue == null)
            return new ArrayList<>();
        try {
            JSONArray array = new JSONArray(databaseValue);
            ArrayList<String> ret = new ArrayList<>();
            for (int i = 0; i < array.length(); i++) {
                ret.add(array.getString(i));
            }
            return ret;
        }
        catch (Exception e) {
            return new ArrayList<>();
        }
    }

    @Override
    public String convertToDatabaseValue(List<String> entityProperty) {
        try {
            if (entityProperty == null)
                return null;
            return new JSONArray(entityProperty).toString();
        }
        catch (Exception e) {
            return null;
        }
    }
}