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Custom Attributes

It is possible to define custom attributes that may be used in predicates, queries and indexes. In order to define a custom attribute, you need to implement a com.hazelcast.query.extractor.ValueExtractor which encompasses the extraction logic.

Implementing ValueExtractor

In order to implement your own ValueExtractor, extend the abstract com.hazelcast.query.extractor.ValueExtractor class and implement the extract method.

The ValueExtractor interface looks as follows:

/***
 * Common superclass for all extractors.
 *
 * @param <T> type of the target object to extract the value from
 * @param <R> type of the result object - the extracted value
 * @see com.hazelcast.query.extractor.MultiResult
 */
public abstract class ValueExtractor<T, R> {

    /**
     * Extracts custom attribute's value from the given target object.
     *
     * @return extracted value
     */
    public abstract R extract(T target);

}

Configuring a Custom Attribute in Programmatically

The following snippet demonstrates how to define a custom attribute using a ValueExtractor.

MapAttributeConfig attributeConfig = new MapAttributeConfig();
attributeConfig.setName("currency");
attributeConfig.setExtractor("com.bank.CurrencyExtractor");

MapConfig mapConfig = new MapConfig();
mapConfig.addMapAttributeConfig(attributeConfig);

currency is the name of the custom attribute that will be extracted using the CurrencyExtractor class.

Configuring a Custom Attribute Declaratively

The following snippet demonstrates how to define a custom attribute in the Hazelcast XML Configuration.

<map name="trades">
   <attributes>
       <attribute extractor="com.bank.CurrencyExtractor">currency</attribute>
   </attributes>
</map>

Analogously to the example above, currency is the name of the custom attribute that will be extracted using the CurrencyExtractor class.

Indexing Custom Attributes

You can also create an index on a Custom Attribute. The name of the attribute used in the index definition has to match the one used in the attributes configuration.

<indexes>
  <index ordered="false">currency</index>
</indexes>