How to implement virtual Attributes?

[vitalizis]

I would like to have an additional column with a modified value from another column: Now I have next code like this but it doesn't work:

const { Model } = require("objection");  
    class TestModel extends Model {
      static get tableName() {
        return "testTable";
      }
    
    
      static get virtualAttributes() {
        return ["someNewField"];
      }
    
      someNewField() {
        return this.someField+'testString';
      }
    
      static get jsonSchema() {
        return {
          type: "object",
          properties: {
            someField:{ type: "string" },
          },
        };
      }
    }
    
    module.exports = {
      TestModel,
    };

I got error like:
"message": "Cannot query field \"someNewField\" on type \"testTable\".",

[CassandraNewell]

I have a similar example working, but I had to add someNewField to the properties list in jsonSchema, and my someNewField() is a getter (not sure if the second part is important or just the first).