SortObserver

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org.apache.derby.iapi.store.access
Interface SortObserver

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.

Method Summary

void addToFreeList(org.apache.derby.iapi.types.DataValueDescriptor[] objectArray, int maxFreeListSize)


org.apache.derby.iapi.types.DataValueDescriptor[] getArrayClone()


org.apache.derby.iapi.types.DataValueDescriptor[] insertDuplicateKey(org.apache.derby.iapi.types.DataValueDescriptor[] insertRow, org.apache.derby.iapi.types.DataValueDescriptor[] existingRow)
          Called prior to inserting a duplicate sort key.

org.apache.derby.iapi.types.DataValueDescriptor[] insertNonDuplicateKey(org.apache.derby.iapi.types.DataValueDescriptor[] insertRow)
          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.

Method Detail

insertNonDuplicateKey

public org.apache.derby.iapi.types.DataValueDescriptor[] insertNonDuplicateKey(org.apache.derby.iapi.types.DataValueDescriptor[] insertRow)
                                                                        throws org.apache.derby.iapi.error.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.

insertDuplicateKey

public org.apache.derby.iapi.types.DataValueDescriptor[] insertDuplicateKey(org.apache.derby.iapi.types.DataValueDescriptor[] insertRow,
                                                                            org.apache.derby.iapi.types.DataValueDescriptor[] existingRow)
                                                                     throws org.apache.derby.iapi.error.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.

addToFreeList

public void addToFreeList(org.apache.derby.iapi.types.DataValueDescriptor[] objectArray,
                          int maxFreeListSize)

getArrayClone

public org.apache.derby.iapi.types.DataValueDescriptor[] getArrayClone()
                                                                throws org.apache.derby.iapi.error.StandardException