svn commit: r386068 - in /db/derby/code/trunk/java: engine/org/apache/derby/impl/sql/execute/ScrollInsensitiveResultSet.java testing/org/apache/derbyTesting/functionTests/tests/lang/scrollCursors2.java

[ka...@apache.org]

Author: kahatlen
Date: Wed Mar 15 05:11:17 2006
New Revision: 386068

URL: http://svn.apache.org/viewcvs?rev=386068&view=rev
Log:
DERBY-992: A corner case bug and missing optimization in
ScrollInsensitiveResultSet

a) For a scrollable, insensitive result set (read-only) which is
   empty, ResultSet#afterLast should have no effect, but erroneously
   sets the internal variable afterLast to true, so that a subsequent
   call to ResultSet#isAfterLast will return 'true' in the embedded
   client. It does not happen on the client driver, because it seems
   to do some double book-keeping for this case.

b) In ScrollInsensitiveResultSet#getNextRowCore and #getAbsoluteRow,
   there are missing checks will cause unnecessary read (attempts)
   from underlying result set even if end has been seen already.

Patch submitted by Dag H. Wanvik.

Modified:
    db/derby/code/trunk/java/engine/org/apache/derby/impl/sql/execute/ScrollInsensitiveResultSet.java
    db/derby/code/trunk/java/testing/org/apache/derbyTesting/functionTests/tests/lang/scrollCursors2.java

Modified: db/derby/code/trunk/java/engine/org/apache/derby/impl/sql/execute/ScrollInsensitiveResultSet.java
URL: http://svn.apache.org/viewcvs/db/derby/code/trunk/java/engine/org/apache/derby/impl/sql/execute/ScrollInsensitiveResultSet.java?rev=386068&r1=386067&r2=386068&view=diff
==============================================================================
--- db/derby/code/trunk/java/engine/org/apache/derby/impl/sql/execute/ScrollInsensitiveResultSet.java (original)
+++ db/derby/code/trunk/java/engine/org/apache/derby/impl/sql/execute/ScrollInsensitiveResultSet.java Wed Mar 15 05:11:17 2006
@@ -239,6 +239,10 @@
                     return null;
 		}
 
+		if (seenLast && row > lastPosition) {
+		   return setAfterLastRow();
+		}		
+
 		if (row > 0)
 		{
 			// position is from the start of the result set
@@ -423,6 +427,10 @@
 		if (!isOpen)
 			throw StandardException.newException(SQLState.LANG_RESULT_SET_NOT_OPEN, "next");
 
+		if (seenLast && currentPosition == lastPosition) {
+		   return setAfterLastRow();
+		}
+
 		/* Should we get the next row from the source or the hash table? */
 		if (currentPosition == positionInSource)
 		{
@@ -600,8 +608,15 @@
 		{
 			getLastRow();
 		}
-		currentPosition = lastPosition + 1;
-		afterLast = true;
+		if (lastPosition == 0) {
+		   // empty rs special case
+		   currentPosition = 0;
+		   afterLast = false;
+		} else {
+		   currentPosition = lastPosition + 1;
+		   afterLast = true;
+		}
+
 		beforeFirst = false;
 		currentRow = null;
 		return null;

Modified: db/derby/code/trunk/java/testing/org/apache/derbyTesting/functionTests/tests/lang/scrollCursors2.java
URL: http://svn.apache.org/viewcvs/db/derby/code/trunk/java/testing/org/apache/derbyTesting/functionTests/tests/lang/scrollCursors2.java?rev=386068&r1=386067&r2=386068&view=diff
==============================================================================
--- db/derby/code/trunk/java/testing/org/apache/derbyTesting/functionTests/tests/lang/scrollCursors2.java (original)
+++ db/derby/code/trunk/java/testing/org/apache/derbyTesting/functionTests/tests/lang/scrollCursors2.java Wed Mar 15 05:11:17 2006
@@ -823,6 +823,20 @@
 		rs.close();
 
 
+		// Empty result set tests (DERBY-992)
+		rs = s_i_r.executeQuery("select * from t where 1=0");
+		rs.afterLast();
+		if (rs.isAfterLast()) {
+			System.out.println("afterLast() on empty RS should be no-op");
+		}
+		
+		rs.beforeFirst(); 
+		if (rs.isBeforeFirst()) {
+			System.out.println("beforeFirst() on empty RS should be no-op");
+		}
+
+		rs.close();
+
 		// Scroll insensitive and updatable
 		s_i_u = conn.createStatement(ResultSet.TYPE_SCROLL_INSENSITIVE,
 									 ResultSet.CONCUR_UPDATABLE);