Hi guys,
today, while I was working on the in-memory btree cursor, I looked at
the testDuplicateKey() test.
There are a few things that I disagree with in this test, or more
specifically on the semantic of next and prev methods. At the beginning
of the test, we start to browse the tree containing 2 elements, 1 and 2 :
public void testDuplicateKey() throws IOException
{
BTreeConfiguration<Integer, Integer> config = new
BTreeConfiguration<Integer, Integer>();
config.setAllowDuplicates( true );
config.setName( "master" );
config.setSerializers( serializer, serializer );
BTree<Integer, Integer> btree = new BTree<Integer, Integer>(
config );
btree.insert( 1, 1 );
btree.insert( 1, 2 );
TupleCursor<Integer, Integer> cursor = btree.browse();
At this point, we are BEFORE the first element, so a call to next()
should return <1, 1>, and it does :
assertTrue( cursor.hasNext() );
Tuple<Integer, Integer> t = cursor.next();
assertEquals( Integer.valueOf( 1 ), t.getKey() );
assertEquals( Integer.valueOf( 1 ), t.getValue() );
If we call next() a second time, we should get <1,2>, and we do :
assertTrue( cursor.hasNext() );
t = cursor.next();
assertEquals( Integer.valueOf( 1 ), t.getKey() );
assertEquals( Integer.valueOf( 2 ), t.getValue() );
There are no next value :
assertFalse( cursor.hasNext() );
Now, the test is moving backward, and here, I disagree. The test is
expercing that doing a prev, we get again the same tuple <1,2> which
makes no sense to me :
// test backward move
assertTrue( cursor.hasPrev() );
t = cursor.prev();
assertEquals( Integer.valueOf( 1 ), t.getKey() );
assertEquals( Integer.valueOf( 2 ), t.getValue() );
We should get instead <1,1>
o--[1]--[2]--x
^
|
+-- btreeBrowse()
o--[1]--[2]--x
^
|
+-- next() : we are on 1
o--[1]--[2]--x
^
|
+-- next() : we are on 2
At this point, a call to prev should move back to [1]
o--[1]--[2]--x
^
|
+-- prev() : we are on 1
My point is that a next or a prev operation should move forward or
backward and return the current element *after* the move, not the opposite.
--
Regards,
Cordialement,
Emmanuel Lécharny
www.iktek.com
