Query List of Custom Objects

Question

I'm unable to find a concrete answer on how to query an Object when it is contained within a List. Perhaps it's in the documentation or forums, but I haven't found it. What I have is a Building Object that contains a List<Room> rooms, and each Room has its own attributes like typeCode. Our cache contains Building Objects indexed by its own key. Now I want to write a Filter to locate 1 to many Building Objects that have a Room with a specific typeCode, say "2DB".
I've tried an EqualsFilter with "2DB" and passing it a ValueExtractor that navigates the Building like: rooms.typeCode. I expect the Building getRooms() method to be called, which returns a List<Room>, and then reflection to evaluate the List contents to call getTypeCode() on each Room instance. Instead, I see errors because getTypeCode() doesn't exist on java.util.ArrayList. No kidding.
How do I get the framework to dive inside the List and evaluate the Room instances inside it? All examples I've seen are for simple collections, like List<String> or List<Integer>, whereas I have a List<FooBar>.

Answer 1

Hi,
you would need to write a custom extractor to achieve this as the out-of-the-box extractors don't support invocation chaining across collections (i.e. extracting a collection created by extracting attributes from collection elements).
something like this:
import java.io.IOException;
import java.lang.reflect.Array;
import java.util.ArrayList;
import java.util.Collection;
import com.tangosol.io.pof.PofReader;
import com.tangosol.io.pof.PofWriter;
import com.tangosol.io.pof.PortableObject;
import com.tangosol.util.ValueExtractor;
public class TwoLevelChainExtractor implements ValueExtractor, PortableObject {
   private ValueExtractor extractorReturningCollection;
   private ValueExtractor extractorExtractingFromCollectionElement;
    * This is for the POF deserialization.
   public TwoLevelChainExtractor() {
   public TwoLevelChainExtractor(ValueExtractor extractorReturningCollection, ValueExtractor extractorExtractingFromCollectionElement) {
      this.extractorReturningCollection = extractorReturningCollection;
      this.extractorExtractingFromCollectionElement = extractorExtractingFromCollectionElement;
   @Override
   public Object extract(Object obj) {
      Object interim = extractorReturningCollection.extract(obj);
      Collection res = new ArrayList();
      ValueExtractor innerExtractor = extractorExtractingFromCollectionElement;
      if (interim instanceof Collection) {
         for (Object element : (Collection) interim) {
            res.add(innerExtractor.extract(element));
      } else if (interim instanceof Object[]) {
         for (Object element : (Object[]) interim) {
            res.add(innerExtractor.extract(element));
      } else {
         Class<? extends Object> cls = interim.getClass();
         if (cls.isArray()) {
            // primitive array
            int count = Array.getLength(interim);
            for (int i=0; i<count; ++i) {
               Object boxedPrimitive = Array.get(interim, i);
               res.add(innerExtractor.extract(boxedPrimitive));
         } else {
            res.add(innerExtractor.extract(interim));
      return res;
   @Override
   public void readExternal(PofReader reader) throws IOException {
      extractorReturningCollection = (ValueExtractor) reader.readObject(0);
      extractorExtractingFromCollectionElement = (ValueExtractor) reader.readObject(1);
   @Override
   public void writeExternal(PofWriter writer) throws IOException {
      writer.writeObject(0, extractorReturningCollection);
      writer.writeObject(1, extractorExtractingFromCollectionElement);
   // equals() and hashCode() are required to be able to use this extractor to create indexes, where the extractor acts as a key in a hash-map
   @Override
   public int hashCode() {
      final int prime = 31;
      int result = 1;
      result = prime * result
            + ((extractorExtractingFromCollectionElement == null) ? 0 : extractorExtractingFromCollectionElement.hashCode());
      result = prime * result + ((extractorReturningCollection == null) ? 0 : extractorReturningCollection.hashCode());
      return result;
   @Override
   public boolean equals(Object obj) {
      if (this == obj)
         return true;
      if (obj == null)
         return false;
      if (getClass() != obj.getClass())
         return false;
      TwoLevelChainExtractor other = (TwoLevelChainExtractor) obj;
      if (extractorExtractingFromCollectionElement == null) {
         if (other.extractorExtractingFromCollectionElement != null)
            return false;
      } else if (!extractorExtractingFromCollectionElement.equals(other.extractorExtractingFromCollectionElement))
         return false;
      if (extractorReturningCollection == null) {
         if (other.extractorReturningCollection != null)
            return false;
      } else if (!extractorReturningCollection.equals(other.extractorReturningCollection))
         return false;
      return true;
}Afterwards you can just use this extractor to extract a collection of type codes from rooms:
ValueExtractor roomsTypeCodes = new TwoLevelChainExtractor(new ReflectionExtractor("getRooms"), new ReflectionExtractor("getTypeCode"));You can use this roomsTypeCodes and a ContainsFilter or ContainsAnyFilter to achieve what you want.
You can implementing similar stuff for POF extraction by leveraging the PofValueParser class in an EntryExtractor subclass.
Best regards,
Robert