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// Copyright 2017 Yahoo Holdings. Licensed under the terms of the Apache 2.0 license. See LICENSE in the project root.
package com.yahoo.search.result;
import com.yahoo.search.query.Sorting;
import java.util.Comparator;
/**
* Comparator used for ordering hits using the field values and a sorting specification.
* <p>
* <b>Note:</b> this comparator imposes orderings that are inconsistent with equals.
* <p>
*
* @author <a href="mailto:steinar@yahoo-inc.com">Steinar Knutsen</a>
*/
// Is tested in HitSortSpecOrdererTestCase
public class FieldComparator extends ChainableComparator {
/** The definition of sorting order */
private Sorting sorting;
/** Creates a field comparator using a sort order and having no chained comparator */
public FieldComparator(Sorting sorting) {
this(sorting,null);
}
/** Creates a field comparator using a sort order with a chained comparator */
public FieldComparator(Sorting sorting,Comparator<Hit> secondaryComparator) {
super(secondaryComparator);
this.sorting = sorting;
}
/** Creates a comparator given a sorting, or returns null if the given sorting is null */
public static FieldComparator create(Sorting sorting) {
if (sorting==null) return null;
return new FieldComparator(sorting);
}
/**
* Compares hits based on a sorting specification and values
* stored in hit fields.0
* <p>
* When one of the hits has the requested property and the other
* has not, the the hit containing the property precedes the one
* that does not.
* <p>
* There is no locale based sorting here, as the backend does
* not do that either.
*
* @return -1, 0, 1 if first should be sorted before, equal to
* or after second
*/
@Override
public int compare(Hit first, Hit second) {
for (Sorting.FieldOrder fieldOrder : sorting.fieldOrders() ) {
String fieldName = fieldOrder.getFieldName();
Object a = getField(first,fieldName);
Object b = getField(second,fieldName);
// If either of the values are null, don't touch the ordering
// This is to avoid problems if the sorting is called before the
// result is filled.
if ((a == null) || (b == null)) return 0;
int x = compareValues(a, b, fieldOrder.getSorter());
if (x != 0) {
if (fieldOrder.getSortOrder() == Sorting.Order.DESCENDING)
x *= -1;
return x;
}
}
return super.compare(first,second);
}
public Object getField(Hit hit,String key) {
if ("[relevance]".equals(key)) return hit.getRelevance();
if ("[rank]".equals(key)) return hit.getRelevance();
if ("[source]".equals(key)) return hit.getSource();
return hit.getField(key);
}
@SuppressWarnings("rawtypes")
private int compareValues(Object first, Object second, Sorting.AttributeSorter s) {
if (first.getClass().isInstance(second)
&& first instanceof Comparable) {
// We now know:
// second is of a type which is a subclass of first's type
// They both implement Comparable
return s.compare((Comparable)first, (Comparable)second);
} else {
return s.compare(first.toString(), second.toString());
}
}
public String toString() {
StringBuilder b = new StringBuilder();
b.append("FieldComparator:");
if (sorting == null) {
b.append(" null");
} else {
b.append(sorting.toString());
}
return b.toString();
}
}
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