java - Realm for Android, how to sync server data to realm database? -

i'm trying sync city list

public class city extends realmobject {     @primarykey     @serializedname("id")     private int id;      @serializedname("title")     private string title;      @serializedname("clubs")     private realmlist<club> clubs; } 

that contains clubs, , club contains various other models. there simple way can make local realm database identical response, if city not returned in json, need remove realm, otherwise update it. current thoughts 2 iterations, 1 update , create new city instances, other remove unneeded ones.

for example, updating user info server, when user has read news saved locally, troublesome is:

private void createorupdateuser(user updated) {     user user = mrealm.where(user.class).equalto("id", updated.getid()).findfirst();      mrealm.begintransaction();      realmlist<realmint> removednews;      if (user != null) {         removednews = new realmlist<>();         removednews.addall(user.getremovednews());     } else {         removednews = new realmlist<>();     }      updated = mrealm.copytorealmorupdate(updated);     updated.setremovednews(removednews);      mrealm.committransaction(); } 

if don't wrap relations arraylist/realmlist , re-set on updated entry, copytorealmorupdate removes them , there's no way them back.

updated.setremovednews(user.getremovednews()); 

has same outcome, when copytorealmorupdate executed, updated user has 0 read news. same goes when replace realmint news model thas has @primarykey.

retrofit2, gson , realm used.