java/src/main/com/google/appengine/api/datastore/BaseQuerySplitter.java

   1 // Copyright 2009 Google Inc. All Rights Reserved.
   2
   3 package com.google.appengine.api.datastore;
   4
   5 import com.google.appengine.api.datastore.Query.SortDirection;
   6
   7 import java.util.Collections;
   8 import java.util.Comparator;
   9
  10 /**
  11  * Base implementation of {@link QuerySplitter} with logic common to all
  12  * splitters.
  13  *
  14  */
  15 abstract class BaseQuerySplitter implements QuerySplitter {
  16   protected static final Comparator<ComparableValue> VALUE_COMPARATOR_ASC =
  17       new Comparator<ComparableValue>() {
  18         @Override
  19         public int compare(ComparableValue o1, ComparableValue o2) {
  20           return EntityProtoComparators.MULTI_TYPE_COMPARATOR.compare(
  21               o1.comparableValue, o2.comparableValue);
  22         }
  23       };
  24
  25   protected static final Comparator<ComparableValue> VALUE_COMPARATOR_DESC =
  26       Collections.reverseOrder(VALUE_COMPARATOR_ASC);
  27
  28   protected BaseQuerySplitter() {
  29   }
  30
  31   /**
  32    * A class that allows arbitrary property values to be compared while
  33    * preserving their original value.
  34    *
  35    * <p>This is needed because converting a value into a {@code
  36    * Comparable<Object>} is potentially destructive (meaning the {@code
  37    * Comparable<Object>} value cannot be used as a property value).
  38    */
  39   protected static class ComparableValue {
  40     private final Comparable<Object> comparableValue;
  41     private final Object originalValue;
  42
  43     public ComparableValue(Object value) {
  44       this.comparableValue = DataTypeTranslator.getComparablePropertyValue(value);
  45       this.originalValue = value;
  46     }
  47
  48     public Object getValue() {
  49       return originalValue;
  50     }
  51   }
  52
  53   protected static Comparator<ComparableValue> getValueComparator(SortDirection sortDirection) {
  54     if (sortDirection == SortDirection.DESCENDING) {
  55       return VALUE_COMPARATOR_DESC;
  56     } else {
  57       return VALUE_COMPARATOR_ASC;
  58     }
  59   }
  60 }