Index: lucene/join/src/java/org/apache/lucene/search/join/ToParentFieldComparator.java
IDEA additional info:
Subsystem: com.intellij.openapi.diff.impl.patch.CharsetEP
<+>UTF-8
===================================================================
--- lucene/join/src/java/org/apache/lucene/search/join/ToParentFieldComparator.java	(revision )
+++ lucene/join/src/java/org/apache/lucene/search/join/ToParentFieldComparator.java	(revision )
@@ -0,0 +1,308 @@
+package org.apache.lucene.search.join;
+
+/*
+ * 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.
+ */
+
+import org.apache.lucene.index.AtomicReaderContext;
+import org.apache.lucene.search.DocIdSet;
+import org.apache.lucene.search.DocIdSetIterator;
+import org.apache.lucene.search.FieldComparator;
+import org.apache.lucene.search.Filter;
+import org.apache.lucene.util.FixedBitSet;
+
+import java.io.IOException;
+
+/**
+ * A field comparator that allows parent documents to be sorted by fields
+ * from the child documents.
+ */
+public abstract class ToParentFieldComparator extends FieldComparator {
+
+  final Filter parentFilter;
+  final Filter childFilter;
+  final int spareSlot;
+
+  FieldComparator wrappedComparator;
+  FixedBitSet parentDocuments;
+  FixedBitSet childDocuments;
+
+  ToParentFieldComparator(FieldComparator wrappedComparator, Filter parentFilter, Filter childFilter, int spareSlot) {
+    this.wrappedComparator = wrappedComparator;
+    this.parentFilter = parentFilter;
+    this.childFilter = childFilter;
+    this.spareSlot = spareSlot;
+  }
+
+  @Override
+  public int compare(int slot1, int slot2) {
+    return wrappedComparator.compare(slot1, slot2);
+  }
+
+  @Override
+  public void setBottom(int slot) {
+    wrappedComparator.setBottom(slot);
+  }
+
+  @Override
+  public FieldComparator setNextReader(AtomicReaderContext context) throws IOException {
+    DocIdSet innerDocuments = childFilter.getDocIdSet(context, null);
+    if (isEmpty(innerDocuments)) {
+      this.childDocuments = null;
+    } else if (innerDocuments instanceof FixedBitSet) {
+      this.childDocuments = (FixedBitSet) innerDocuments;
+    } else {
+      this.childDocuments = toFixedBitSet(innerDocuments.iterator(), context.reader().maxDoc());
+    }
+    DocIdSet rootDocuments = parentFilter.getDocIdSet(context, null);
+    if (isEmpty(rootDocuments)) {
+      this.parentDocuments = null;
+    } else if (rootDocuments instanceof FixedBitSet) {
+      this.parentDocuments = (FixedBitSet) rootDocuments;
+    } else {
+      this.parentDocuments = toFixedBitSet(rootDocuments.iterator(), context.reader().maxDoc());
+    }
+
+    wrappedComparator = wrappedComparator.setNextReader(context);
+    return this;
+  }
+
+  private static boolean isEmpty(DocIdSet set) {
+    return set == null || set == DocIdSet.EMPTY_DOCIDSET;
+  }
+
+  private static FixedBitSet toFixedBitSet(DocIdSetIterator iterator, int numBits) throws IOException {
+    FixedBitSet set = new FixedBitSet(numBits);
+    int doc;
+    while ((doc = iterator.nextDoc()) != DocIdSetIterator.NO_MORE_DOCS) {
+      set.set(doc);
+    }
+    return set;
+  }
+
+  @Override
+  public Object value(int slot) {
+    return wrappedComparator.value(slot);
+  }
+
+  final static class Lowest extends ToParentFieldComparator {
+
+    Lowest(FieldComparator wrappedComparator, Filter parentFilter, Filter childFilter, int spareSlot) {
+      super(wrappedComparator, parentFilter, childFilter, spareSlot);
+    }
+
+    @Override
+    public int compareBottom(int rootDoc) throws IOException {
+      if (rootDoc == 0 || parentDocuments == null || childDocuments == null) {
+        return 0;
+      }
+
+      // We need to copy the lowest value from all nested docs into slot.
+      int prevRootDoc = parentDocuments.prevSetBit(rootDoc - 1);
+      int nestedDoc = childDocuments.nextSetBit(prevRootDoc + 1);
+      if (nestedDoc >= rootDoc || nestedDoc == -1) {
+        return 0;
+      }
+
+      // We only need to emit a single cmp value for any matching nested doc
+      int cmp = wrappedComparator.compareBottom(nestedDoc);
+      if (cmp > 0) {
+        return cmp;
+      }
+
+      while (true) {
+        nestedDoc = childDocuments.nextSetBit(nestedDoc + 1);
+        if (nestedDoc >= rootDoc || nestedDoc == -1) {
+          return cmp;
+        }
+        int cmp1 = wrappedComparator.compareBottom(nestedDoc);
+        if (cmp1 > 0) {
+          return cmp1;
+        } else {
+          if (cmp1 == 0) {
+            cmp = 0;
+          }
+        }
+      }
+    }
+
+    @Override
+    public void copy(int slot, int rootDoc) throws IOException {
+      if (rootDoc == 0 || parentDocuments == null || childDocuments == null) {
+        return;
+      }
+
+      // We need to copy the lowest value from all nested docs into slot.
+      int prevRootDoc = parentDocuments.prevSetBit(rootDoc - 1);
+      int nestedDoc = childDocuments.nextSetBit(prevRootDoc + 1);
+      if (nestedDoc >= rootDoc || nestedDoc == -1) {
+        return;
+      }
+      wrappedComparator.copy(spareSlot, nestedDoc);
+      wrappedComparator.copy(slot, nestedDoc);
+
+      while (true) {
+        nestedDoc = childDocuments.nextSetBit(nestedDoc + 1);
+        if (nestedDoc >= rootDoc || nestedDoc == -1) {
+          return;
+        }
+        wrappedComparator.copy(spareSlot, nestedDoc);
+        if (wrappedComparator.compare(spareSlot, slot) < 0) {
+          wrappedComparator.copy(slot, nestedDoc);
+        }
+      }
+    }
+
+    @Override
+    @SuppressWarnings("unchecked")
+    public int compareDocToValue(int rootDoc, Object value) throws IOException {
+      if (rootDoc == 0 || parentDocuments == null || childDocuments == null) {
+        return 0;
+      }
+
+      // We need to copy the lowest value from all nested docs into slot.
+      int prevRootDoc = parentDocuments.prevSetBit(rootDoc - 1);
+      int nestedDoc = childDocuments.nextSetBit(prevRootDoc + 1);
+      if (nestedDoc >= rootDoc || nestedDoc == -1) {
+        return 0;
+      }
+
+      // We only need to emit a single cmp value for any matching nested doc
+      int cmp = wrappedComparator.compareBottom(nestedDoc);
+      if (cmp > 0) {
+        return cmp;
+      }
+
+      while (true) {
+        nestedDoc = childDocuments.nextSetBit(nestedDoc + 1);
+        if (nestedDoc >= rootDoc || nestedDoc == -1) {
+          return cmp;
+        }
+        int cmp1 = wrappedComparator.compareDocToValue(nestedDoc, value);
+        if (cmp1 > 0) {
+          return cmp1;
+        } else {
+          if (cmp1 == 0) {
+            cmp = 0;
+          }
+        }
+      }
+    }
+
+  }
+
+  final static class Highest extends ToParentFieldComparator {
+
+    Highest(FieldComparator wrappedComparator, Filter parentFilter, Filter childFilter, int spareSlot) {
+      super(wrappedComparator, parentFilter, childFilter, spareSlot);
+    }
+
+    @Override
+    public int compareBottom(int rootDoc) throws IOException {
+      if (rootDoc == 0 || parentDocuments == null || childDocuments == null) {
+        return 0;
+      }
+
+      int prevRootDoc = parentDocuments.prevSetBit(rootDoc - 1);
+      int nestedDoc = childDocuments.nextSetBit(prevRootDoc + 1);
+      if (nestedDoc >= rootDoc || nestedDoc == -1) {
+        return 0;
+      }
+
+      int cmp = wrappedComparator.compareBottom(nestedDoc);
+      if (cmp < 0) {
+        return cmp;
+      }
+
+      while (true) {
+        nestedDoc = childDocuments.nextSetBit(nestedDoc + 1);
+        if (nestedDoc >= rootDoc || nestedDoc == -1) {
+          return cmp;
+        }
+        int cmp1 = wrappedComparator.compareBottom(nestedDoc);
+        if (cmp1 < 0) {
+          return cmp1;
+        } else {
+          if (cmp1 == 0) {
+            cmp = 0;
+          }
+        }
+      }
+    }
+
+    @Override
+    public void copy(int slot, int rootDoc) throws IOException {
+      if (rootDoc == 0 || parentDocuments == null || childDocuments == null) {
+        return;
+      }
+
+      int prevRootDoc = parentDocuments.prevSetBit(rootDoc - 1);
+      int nestedDoc = childDocuments.nextSetBit(prevRootDoc + 1);
+      if (nestedDoc >= rootDoc || nestedDoc == -1) {
+        return;
+      }
+      wrappedComparator.copy(spareSlot, nestedDoc);
+      wrappedComparator.copy(slot, nestedDoc);
+
+      while (true) {
+        nestedDoc = childDocuments.nextSetBit(nestedDoc + 1);
+        if (nestedDoc >= rootDoc || nestedDoc == -1) {
+          return;
+        }
+        wrappedComparator.copy(spareSlot, nestedDoc);
+        if (wrappedComparator.compare(spareSlot, slot) > 0) {
+          wrappedComparator.copy(slot, nestedDoc);
+        }
+      }
+    }
+
+    @Override
+    @SuppressWarnings("unchecked")
+    public int compareDocToValue(int rootDoc, Object value) throws IOException {
+      if (rootDoc == 0 || parentDocuments == null || childDocuments == null) {
+        return 0;
+      }
+
+      int prevRootDoc = parentDocuments.prevSetBit(rootDoc - 1);
+      int nestedDoc = childDocuments.nextSetBit(prevRootDoc + 1);
+      if (nestedDoc >= rootDoc || nestedDoc == -1) {
+        return 0;
+      }
+
+      int cmp = wrappedComparator.compareBottom(nestedDoc);
+      if (cmp < 0) {
+        return cmp;
+      }
+
+      while (true) {
+        nestedDoc = childDocuments.nextSetBit(nestedDoc + 1);
+        if (nestedDoc >= rootDoc || nestedDoc == -1) {
+          return cmp;
+        }
+        int cmp1 = wrappedComparator.compareDocToValue(nestedDoc, value);
+        if (cmp1 < 0) {
+          return cmp1;
+        } else {
+          if (cmp1 == 0) {
+            cmp = 0;
+          }
+        }
+      }
+    }
+
+  }
+
+}
Index: lucene/join/src/java/org/apache/lucene/search/join/ToParentFieldComparatorSource.java
IDEA additional info:
Subsystem: com.intellij.openapi.diff.impl.patch.CharsetEP
<+>UTF-8
===================================================================
--- lucene/join/src/java/org/apache/lucene/search/join/ToParentFieldComparatorSource.java	(revision )
+++ lucene/join/src/java/org/apache/lucene/search/join/ToParentFieldComparatorSource.java	(revision )
@@ -0,0 +1,67 @@
+package org.apache.lucene.search.join;
+
+/*
+ * 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.
+ */
+
+import org.apache.lucene.search.FieldComparator;
+import org.apache.lucene.search.FieldComparatorSource;
+import org.apache.lucene.search.Filter;
+import org.apache.lucene.search.MatchAllDocsQuery;
+import org.apache.lucene.search.QueryWrapperFilter;
+
+import java.io.IOException;
+
+/**
+ * Provides a {@link ToParentFieldComparator}, that allows sorting parent docs based on child level fields.
+ * Based on the sort order it either takes the document with the lowest or highest field value into account.
+ */
+public class ToParentFieldComparatorSource extends FieldComparatorSource {
+
+  private final FieldComparatorSource childSource;
+  private final Filter parentFilter;
+  private final Filter childFilter;
+
+  /**
+   * @param childSource Provides the field comparator for fields on the child document level.
+   * @param parentFilter The filter marking the parent documents
+   * @param childFilter The filter that child documents need to apply with in order to be taken into account during
+   *                    sorting.
+   */
+  public ToParentFieldComparatorSource(FieldComparatorSource childSource, Filter parentFilter, Filter childFilter) {
+    this.childSource = childSource;
+    this.parentFilter = parentFilter;
+    this.childFilter = childFilter;
+  }
+
+  // In the case
+  public ToParentFieldComparatorSource(FieldComparatorSource childSource, Filter parentFilter) {
+    this.childSource = childSource;
+    this.parentFilter = parentFilter;
+    this.childFilter = new QueryWrapperFilter(new MatchAllDocsQuery());
+  }
+
+  @Override
+  public FieldComparator<?> newComparator(String fieldname, int numHits, int sortPos, boolean reversed) throws IOException {
+    // +1: have one spare slot for value comparison between inner documents.
+    FieldComparator wrappedComparator = childSource.newComparator(fieldname, numHits + 1, sortPos, reversed);
+    if (reversed) {
+      return new ToParentFieldComparator.Highest(wrappedComparator, parentFilter, childFilter, numHits);
+    } else {
+      return new ToParentFieldComparator.Lowest(wrappedComparator, parentFilter, childFilter, numHits);
+    }
+  }
+}