object/src/main/java/com/orientechnologies/orient/core/entity/OEntityManager.java
public synchronized void setClassHandler(final OEntityManagerClassHandler iClassHandler) {
    Iterator<Entry<String, Class<?>>> iterator = classHandler.getClassesEntrySet().iterator();
    while (iterator.hasNext()){
      Entry<String, Class<?>> entry = iterator.next();
      boolean forceSchemaReload = !iterator.hasNext();
      iClassHandler.registerEntityClass(entry.getValue(), forceSchemaReload);
    }
    this.classHandler = iClassHandler;
  }
public synchronized void setClassHandler(final OEntityManagerClassHandler iClassHandler) {
    Iterator<Entry<String, Class<?>>> iterator = classHandler.getClassesEntrySet().iterator();
    while (iterator.hasNext()){
      Entry<String, Class<?>> entry = iterator.next();
      boolean forceSchemaReload = !iterator.hasNext();
      iClassHandler.registerEntityClass(entry.getValue(), forceSchemaReload);
    }
    this.classHandler = iClassHandler;
  }
Sets the received handler as default and merges the classes all together.

@param iClassHandler