code: public ZooJdoProperties setRetainValues(boolean flag) {
      	DBTracer.logCall(this, flag); 
  		put(Constants.PROPERTY_RETAIN_VALUES, Boolean.toString(flag));
  		return this;
  	}
docs: Whether values should be retained after commit(). By default objects are evicted.
  @param flag The flag
  @return this
  @see Constants#PROPERTY_RETAIN_VALUES