adding a function to an ObjectType class

[shawnjones253]

I'd like to be able to add static functions to ObjectType classes to support mapping to/from internal service types:

@ObjectType()
export class MyApiReturnType {
  @Field(() => String, { nullable: true })
  someField?: string | null

  static fromSomeInternalType(internalType: InternalType): MyApiReturnType {
    const myApiReturnType = new MyApiReturnType()
    myApiReturnType.someField = internalType.someField

    return myApiReturnType
  }
}

this results in: TypeError: MyApiReturnType.fromSomeInternalType is not a function

I also tried:

@ObjectType()
export class MyApiReturnType {
  @Field(() => String, { nullable: true })
  someField?: string | null
}

export function myApiReturnTypeFromSomeInternalType(internalType: InternalType): MyApiReturnType {
    const myApiReturnType = new MyApiReturnType()
    myApiReturnType.someField = internalType.someField

    return myApiReturnType
}

but that results in: TypeError: Cannot assign to read only property 'someField' of object '#<_MyApiReturnType>'

Any suggestions?

[shawnjones253]

additionally, I've tried Object.assign as in this example but had the same "read only property" TypeError.