# IndexedElementRecord.java

    package org.codefilarete.stalactite.engine.configurer.elementcollection;

    import org.codefilarete.reflection.PropertyAccessor;
    import org.codefilarete.stalactite.engine.diff.CollectionDiffer;

    /**
     * Represents a line in table storage, acts as a wrapper of an indexed element collection with source bean identifier addition.
     *
     * @param <TRGT> raw value type (element collection type)
     * @param <ID> source bean identifier type
     */
    public class IndexedElementRecord<TRGT, ID> extends ElementRecord<TRGT, ID> {

    	public static final PropertyAccessor<IndexedElementRecord<Object, Object>, Integer> INDEX_ACCESSOR = PropertyAccessor.fromMethodReference(
    			IndexedElementRecord::getIndex,
    			IndexedElementRecord::setIndex);

    	private int index;

    	/**
    	 * Default constructor for select instantiation
    	 */
    	public IndexedElementRecord() {
    	}

    	public IndexedElementRecord(ID id, TRGT element, int index) {
    		super(id, element);
    		this.index = index;
    	}

    	public int getIndex() {
    		return index;
    	}

    	public void setIndex(int index) {
    		this.index = index;
    	}

    	/**
    	 * Identifier for {@link CollectionDiffer} support (update use case), because it compares beans
    	 * through their "footprint" which is their id in default/entity case, but since we are a value type, we must provide a dedicated footprint.
    	 * Could be hashCode() if it was implemented on identifier + element, but implementing it would require implementing equals() (to comply
    	 * with best practices) which is not our case nor required by {@link CollectionDiffer}.
    	 * Note : name of this method is not important
    	 */
    	public int footprint() {
    		return super.footprint() + 31 * index;
    	}
    }