java/src/main/com/google/appengine/api/labs/datastore/overlay/IdAllocationPolicyInterface.java

   1 package com.google.appengine.api.labs.datastore.overlay;
   2
   3 /**
   4  * An allocation policy for Datastore key IDs.
   5  *
   6  * Key IDs are 52 bits and are formed from a unique sequential counter value provided by the
   7  * backend. The map of (counter value, ID policy) to valid IDs is one-to-one.
   8  */
   9 interface IdAllocationPolicyInterface {
  10   /** Indicates whether {@code id} belongs to the ID range of this policy. */
  11   boolean containsId(long id);
  12
  13   /** The maximum counter value that can be mapped in this policy's ID range. */
  14   long getMaximumCounterValue();
  15
  16   /**
  17    * Converts a counter value to an ID.
  18    *
  19    * @param counter the counter value to convert to an ID.
  20    * @return the ID corresponding to the given counter value.
  21    * @throws IllegalArgumentException if the counter is not in the range
  22    *         @{code [1, getMaximumCounterValue()]}.
  23    */
  24   long counterToId(long counter);
  25
  26   /**
  27    * Converts an ID to the counter value which
  28    * generated it. If the ID does not belong to the range managed by
  29    * this policy.
  30    *
  31    * @param id the entity id to convert to a counter value.
  32    * @return the counter value corresponding to the given entity id.
  33    * @throws IllegalArgumentException if the ID does not belong to the range mapped by this policy.
  34    */
  35   long idToCounter(long id);
  36
  37 }