Interface SortObserver

All Known Implementing Classes:
AggregateSortObserver, BasicSortObserver, UniqueIndexSortObserver, UniqueWithDuplicateNullsIndexSortObserver

public interface SortObserver
A SortObserver is an object that is used as a callback by the sorter. It allows the sort client to do whatever they want from the context of a sort. It contains 2 callback methods: insertDuplicateKey() and insertNonDuplicateKey(). On each SortController.insert(), one or the other of these methods will be called, depending on whether the given row has a key that has been seen before or not.

Some sample uses include:

  • Sorts from Language: Language typically recycles data type wrappers. So the language layer uses SortObservers to clone rows that are kept by the sorter.
  • Distinct sorts: The sorter will call the sort observer each time it identifies a duplicate row. Based on what the sort observer returns to the sorter, the sorter will either retain (insert) the duplicate row, or discard the duplicate row. All you have to do to implement a distinct sort is to tell the sorter to discard the row (return null from insertDuplicateKey()). Also, if you want to throw an exception on a duplicate (e.g. create a unique index), you can just throw an exception from your SortObserver.
  • Aggregates: Vector (grouped) aggregates typically require a sort. Language can use a SortObserver to perform aggregations as duplicate elements are encountered. Scalar aggregates can also be computed using a SortObserver.
These are possible uses only. You, kind reader, may do whatever you wish with this forgiving interface.
See Also:
  • Method Details

    • insertNonDuplicateKey

      DataValueDescriptor[] insertNonDuplicateKey(DataValueDescriptor[] insertRow) throws StandardException
      Called prior to inserting a distinct sort key; in other words, the first time that a key is inserted into the sorter, this method is called. Subsequent inserts with the same key generate a call to insertDuplicateKey() instead.

      This method will most commonly be used to clone the row that is retained by the sorter, or possibly to do some initialization of that row.

      Parameters:
      insertRow - the current row that the sorter is on the verge of retaining
      Returns:
      the row to be inserted by the sorter. If null, then nothing is inserted by the sorter.
      Throws:
      StandardException - either on unexpected exception, or on expected user error that is to percolate back to the driver of the sort.
    • insertDuplicateKey

      DataValueDescriptor[] insertDuplicateKey(DataValueDescriptor[] insertRow, DataValueDescriptor[] existingRow) throws StandardException
      Called prior to inserting a duplicate sort key. This method will typically be used to perform some aggregation on a row that is going to be discarded by the sorter.
      Parameters:
      insertRow - the current row that the sorter is on the verge of retaining. It is a duplicate of existingRow.
      existingRow - the row that is already in the the sorter which is a duplicate of insertRow
      Returns:
      the row to be inserted by the sorter. If null, then nothing is inserted by the sorter. Distinct sorts will want to return null.
      Throws:
      StandardException - either on unexpected exception, or on expected user error that is to percolate back to the driver of the sort.
    • addToFreeList

      void addToFreeList(DataValueDescriptor[] objectArray, int maxFreeListSize)
    • getArrayClone

      DataValueDescriptor[] getArrayClone() throws StandardException
      Throws:
      StandardException
    • deferrable

      boolean deferrable()
      Overridden by subclasses that observe sorters with uniqueness checking.
      Returns:
      true if the index's constraint is deferrable. Any SortObserver implementations that implement uniqueness checking need to keep track of this information.
    • deferred

      boolean deferred()
      Overridden by subclasses that observe sorters with uniqueness checking.
      Returns:
      true if constraint mode of the index's constraint is effectively deferred. Any SortObserver implementations that implement uniqueness checking need to keep track of this information.
    • rememberDuplicate

      void rememberDuplicate(DataValueDescriptor[] row) throws StandardException
      Overridden by subclasses that observe sorters with uniqueness checking. Will be called by sorters iff deferrable() and deferred() and uniqueness violation, so implementations that sometimes return true to these must implement this method to save duplicate information till commit time.
      Parameters:
      row - data of offending key
      Throws:
      StandardException - standard error policy