javascript: JOI merge fields conditionally

Haven’t found any working solution for my case, so I’m creating a new one.
I’ve got this architecture:

function getParts1() {
  return {
    common: joi.object({
      common_key: joi.number().integer().required(),
      common_conditional: joi.string().valid("AB", "CD", "EF").required(),
      common_value1: joi.string().max(144).required(),
    }),

    variation1: joi.object({
      field1: joi.number().allow(0).required(),
      field2: joi.string().max(255).allow("").required(),
    }),

    variation2: joi.object({
      another_field1: joi.number().allow(0).required(),
      another_field2: joi.string().max(255).allow("").required(),
    }),

    variation3: joi.object({
      super_another_field1: joi.number().allow(0).required(),
      super_another_field2: joi.string().max(255).allow("").required(),
    }),
  };
}

function getParts2() {}; //And much more functions like getParts1 with the same keys but different objects as values 

I need to create a function that can work with the output of this kind of functions in the next way:

• Initially it will get a common part from resulting array.
• Then it conditionally merge other variations, condition based on value of common_conditional. In this example I need to merge to array.common keys from array.variation1 if array.common.common_conditional == "AB", variation2 if "CD", etc. It can be much more.

Because of difference in joi.object(...) of each variation for each Parts, I can’t find any solution for this problem.

For example, for the code above if such schema will be created:

const schema = getSchemaFromParts(getParts1());

const data1 = {
  common_key: 12,
  common_conditional: "AB",
  common_value1: "somevalue",
  field1: 14,
  field2: "Value for field2"
}

const data2 = {
  common_key: 16,
  common_conditional: "CD",
  common_value1: "somevalue2",
  another_field1: 18,
  another_field2: "Hello world"
}

const data3 = {
  common_key: 16,
  common_conditional: "EF",
  common_value1: "somevalue3",
  another_field1: 20,
  another_field2: "Broken data"
}

const res1 = schema.validate(data1);
const res2 = schema.validate(data2);
const res3 = schema.validate(data3);
console.log(res1.error)
console.log(res2.error)
console.log(res3.error)

It should pass the res1 and res2, but res3 should throw an error of ValidationError: "another_field1" is not allowed { …(2) }.
Is there any solutions for this case, or maybe it’s better to create a different architecture for the Parts function?