https://medium.com/@aronbalog/spring-boot-kotlin-graphql-mongodb-part-2-mutations-f825033bbfd3

PersonDao.kt

package com.example.demo.dao

import com.example.demo.repository.PersonRepository
import org.springframework.stereotype.Component

@Component
class PersonDao(
        private val personRepository: PersonRepository
) {
    fun getPersonById(id: String) =
            personRepository.findById(id)

    fun getPersonsByName(name: String) =
            personRepository.findByNameLike(name)

    fun createPerson(name: String) =
            personRepository.save(Person(name = name))
}