Can you create an index on a Map?

Question

I have a few questions that I can't seem to figure out nor find a viable example for. Can you create an index for a Map contained within a nested object, and if so, how would you do this? I currently have a Filter the inspects this criteria in the cache but am unable to figure out to create a usabe index for the custom filter. I'm using Coherence 3.5.2 - any help would be most appreciated. I'm not sure if/what I need to do with the SimpleMapIndex....
Here's the basic object map below. My filter is retrieving all of the CustomerGroup objects that have a Customer in it's collection that contains the passed in Integer value in the Customer's Map. So can you create an Index on a Map (and a nested one at that) and how do you that? The index would need to be on the nested customerValues hashmap.
class CustomerGroup
    Set<Customer> customers ;
class Customer
    Map<Integer, CustumerValue> customerValues;
}

Answer 1

If you write a custom ValueExtractor, which you need to create an index, then you will not need a custom Filter.
Depending on how efficient you need to be you custom extractor can use POF and not have to deserialize the entries to create the index, or it can deserialize the class, which will make the code more straight forward.
For example, without using POF
public class MapKeyExtractor extends EntryExtractor implements PortableObject {
    public MapKeyExtractor() {
    @Override
    public Object extractFromEntry(Map.Entry entry) {
        Set<Integer> keys = new HashSet<Integer>();
        CustomerGroup group = (CustomerGroup) entry.getValue();
        Set<Customer> customers = group.getCustomers();
        for (Customer customer : customers) {
            keys.addAll(customer.getCustomerValues().keySet());
        return keys;
    @Override
    public boolean equals(Object obj) {
        return (obj instanceof MapKeyExtractor);
    @Override
    public int hashCode() {
        return MapKeyExtractor.class.hashCode();
    @Override
    public void readExternal(PofReader in) throws IOException {
        super.readExternal(in);
    @Override
    public void writeExternal(PofWriter out) throws IOException {
        super.writeExternal(out);
}The extractor above will return a collection of all of the Integer values in the keys of all the customerValues of all the customers in a CustomerGroup (I have guessed you might have accessor methods on the classes you posted).
You can then use a ContainsFilter for your query. For example to get all the values from the cache where the customerValues map contains a 19 in the key...
Set results = cache.entrySet(new ContainsFilter(new MapKeyExtractor(), 19));You could write a version of the MapKeyExtractor that uses POF and would not deserialize the values but this would be more complicated code as it would need to extract the Map from the POF stream of the value and walk down the keys and values extracting the keys. It is doable but not worth it unless you are really worried about performance of index updates.
Discalimer I have written the code above from the top of my head so have not compiled it or tested it but it should be OK.
JK