code: public boolean restricted(Filter<?> filter) {
  		if (!filter.property().metamodel().isRoot()) {
  			return true;
  		}
  		
  		if (filter instanceof ComparableFilter<?>) {
  			ComparableFilter<?> comparableFilter = (ComparableFilter<?>) filter;
  			Operator operator = comparableFilter.operator();
  			
  			if (operator != Operator.EQUAL_TO) {
  				if (this.filter != null && this.filter.property() != filter.property()) {
  					return true;
  				}
  				
  				this.filter = filter;
  			}
  		}
  		
  		return false;
  	}
docs: Indicates whether the specified {@code Filter} is restricted to Google
  App Engine datastore query or not.
  This method indicates the following cases as <b>restricted</b>:
  <ul>
  <li>
  Property that the specified filter targets is not a root entity's
  property.
  </li>
  <li>
  Operator type of the specified filter is inequality and the property that
  the specified filter targets is not same as the previous filter's one.
  </li>
  </ul>
  
  @param filter The filter to be indicated whether restricted or not.
  @return Whether the specified {@code Filter} is restricted to Google App
  Engine datastore query or not.