Method readNext

src/java/simpledb/index/BTreeFile.java:1437–1473

Read the next tuple either from the current page if it has more tuples matching the predicate or from the next page by following the right sibling pointer. @return the next tuple matching the predicate, or null if none exists

()

	 * @return the next tuple matching the predicate, or null if none exists
	 */
	@Override
	protected Tuple readNext() throws TransactionAbortedException, DbException,
	NoSuchElementException {
		while (it != null) {

			while (it.hasNext()) {
				Tuple t = it.next();
				if (t.getField(f.keyField()).compare(ipred.getOp(), ipred.getField())) {
					return t;
				}
				else if(ipred.getOp() == Op.LESS_THAN || ipred.getOp() == Op.LESS_THAN_OR_EQ) {
					// if the predicate was not satisfied and the operation is less than, we have
					// hit the end
					return null;
				}
				else if(ipred.getOp() == Op.EQUALS && 
						t.getField(f.keyField()).compare(Op.GREATER_THAN, ipred.getField())) {
					// if the tuple is now greater than the field passed in and the operation
					// is equals, we have reached the end
					return null;
				}
			}

			BTreePageId nextp = curp.getRightSiblingId();
			// if there are no more pages to the right, end the iteration
			if(nextp == null) {
				return null;
			}
			else {
				curp = (BTreeLeafPage) Database.getBufferPool().getPage(tid,
						nextp, Permissions.READ_ONLY);
				it = curp.iterator();
			}
		}

		return null;
	}

	/**
	 * rewind this iterator back to the beginning of the tuples