SOLR-264: Added RandomSortField a random order SortComparatorSource. Thanks yonik for the performance hints

git-svn-id: https://svn.apache.org/repos/asf/lucene/solr/trunk@548594 13f79535-47bb-0310-9956-ffa450edef68

CHANGES.txt

@@ -65,6 +65,9 @@ New Features
     requests depending on the request attributes.  This class will likely 
     replace XmlUpdateRequestHandler.  (Thorsten Scherler, ryan)
 
+ 9. SOLR-264: Added RandomSortField, a utility field with a random sort order.
+    This field type should only be used for sorting. (ryan) 
+
 Changes in runtime behavior
 
 Optimizations

src/java/org/apache/solr/schema/RandomSortField.java

@@ -0,0 +1,108 @@
+/**
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.apache.solr.schema;
+
+import java.io.IOException;
+import java.util.Random;
+
+import org.apache.lucene.document.Fieldable;
+import org.apache.lucene.index.IndexReader;
+import org.apache.lucene.search.ScoreDoc;
+import org.apache.lucene.search.ScoreDocComparator;
+import org.apache.lucene.search.SortComparatorSource;
+import org.apache.lucene.search.SortField;
+import org.apache.solr.request.TextResponseWriter;
+import org.apache.solr.request.XMLWriter;
+import org.apache.solr.search.function.ValueSource;
+
+/**
+ * Utility Field used for random sorting.  It should not be passed a value.
+ * 
+ * To enable random sorting, you will need to add something like this 
+ * to the schema.xml
+ * 
+ * <types>
+ *  ...
+ *  <fieldType name="random" class="solr.RandomSortField" />
+ *  ... 
+ * </types>
+ * <fields>
+ *  ...
+ *  <field name="random" type="random" indexed="true" stored="false"/>
+ *  ...
+ * </fields>
+ *  
+ * @author ryan
+ * @version $Id$
+ * @since solr 1.3
+ */
+public class RandomSortField extends FieldType 
+{
+  /** Special comparator for sorting hits in random order */
+  private static final ScoreDocComparator COMPARE = new ScoreDocComparator() {
+    final Random rand = new Random();
+    
+    public int compare (ScoreDoc i, ScoreDoc j) {
+      return (rand.nextBoolean()) ? 1 : -1; //rand.nextInt() >>> 31; ??
+    }
+    public Comparable sortValue (ScoreDoc i) {
+      return new Float(rand.nextFloat());
+    }
+    public int sortType() {
+      return SortField.CUSTOM;
+    }
+  };
+  
+  /** use random sorting order.  */
+  private static class RandomSort extends SortField {
+    public RandomSort( String n )
+    {
+      super( n, SortField.CUSTOM );
+    }
+
+    @Override
+    public SortComparatorSource getFactory() {
+      return new SortComparatorSource() {
+        public ScoreDocComparator newComparator(IndexReader reader, String fieldname) throws IOException {
+          return COMPARE;
+        }
+      };
+    }
+  }
+  
+  @Override
+  public SortField getSortField(SchemaField field,boolean reverse) {
+    return new RandomSort(field.getName());
+  }
+
+  @Override
+  public ValueSource getValueSource(SchemaField field) {
+    throw new UnsupportedOperationException("Random field does not have a value source");
+  }
+
+  @Override
+  public void write(XMLWriter xmlWriter, String name, Fieldable f) {}
+
+  @Override
+  public void write(TextResponseWriter writer, String name, Fieldable f) {}
+}
+
+
+
+
+