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

   1 // Copyright 2012 Google Inc. All Rights Reserved.
   2
   3 package com.google.appengine.api.datastore;
   4
   5 import com.google.common.collect.Lists;
   6 import com.google.storage.onestore.v3.OnestoreEntity.Index.Property;
   7 import com.google.storage.onestore.v3.OnestoreEntity.Index.Property.Direction;
   8
   9 import java.util.List;
  10 import java.util.ListIterator;
  11
  12 /**
  13  * Implements an IndexComponent for an ordered list of properties.
  14  *
  15  * Currently, this is used for ordering constraints.
  16  *
  17  */
  18 class OrderedIndexComponent implements IndexComponent {
  19   private final List<Property> matcherProperties;
  20
  21   public OrderedIndexComponent(List<Property> orderedGroup) {
  22     this.matcherProperties = orderedGroup;
  23   }
  24
  25   @Override
  26   public boolean matches(List<Property> indexProperties) {
  27     ListIterator<Property> indexItr = indexProperties.listIterator(indexProperties.size());
  28     ListIterator<Property> matcherItr = matcherProperties.listIterator(matcherProperties.size());
  29     while (indexItr.hasPrevious() && matcherItr.hasPrevious()) {
  30       if (!propertySatisfies(matcherItr.previous(), indexItr.previous())) {
  31         return false;
  32       }
  33     }
  34     return !matcherItr.hasPrevious();
  35   }
  36
  37   @Override
  38   public List<Property> preferredIndexProperties() {
  39     List<Property> indexProps = Lists.newArrayListWithExpectedSize(matcherProperties.size());
  40     for (Property prop : matcherProperties) {
  41       if (!prop.hasDirection()) {
  42         prop = prop.clone();
  43         prop.setDirection(Direction.ASCENDING);
  44       }
  45       indexProps.add(prop);
  46     }
  47     return indexProps;
  48   }
  49
  50   @Override
  51   public int size() {
  52     return matcherProperties.size();
  53   }
  54
  55   @Override
  56   public String toString() {
  57     return "OrderedIndexComponent: " + matcherProperties;
  58   }
  59
  60   /**
  61    * A {@link Property} satisfies a constraint if it is equal to the constraint. However,
  62    * if the constraint does not specify a direction, then the direction of the actual
  63    * property does not matter.
  64    */
  65   private boolean propertySatisfies(Property constraint, Property property) {
  66     return constraint.equals(property) ||
  67         (!constraint.hasDirection() && constraint.getName().equals(property.getName()));
  68   }
  69
  70 }