worker.java

class SampleWorker extends OffixWorker{

  public doWork(){

     /* getListOfMutations() returns the list of mutations stored in database in the library.
         It's present in the parent class, i.e OffixWorker.
     */
     List<Mutation> listOfMutations=getListOfMutations();

      //get the mutation one by one from list.
      for(int i=0;i<listOfMutations.size();i++){

      Mutation storedmutation = listOfMutations.get(i);

      com.apollographql.apollo.api.Mutation<Operation.Data,Operation.Data,Operation.Variables>         
      obj=Offix.getMutation(storedmutation);

      ApolloMutationCall<Operation.Data> customClient= apolloClient.mutate(obj);

      customClient?.enqueue(object : ApolloCall.Callback<Operation.Data>() {
          override fun onFailure(e: ApolloException) {
                   e.printStackTrace()
          }

          /* On getting a successful response back from the server, delete mutation from the database.
          */
          override fun onResponse(response: Response<Operation.Data>) {
               // Do your work and delete that mutation by calling the deleteMutation() function.
               deleteMutation(storedmutation)
          }
     })
  return Result.success();
}