protected Iterator<MessageForRender> getMessages(
FacesContext context, String forClientId, UIComponent component) {
Iterator<MessageForRender> msgIter;
if (forClientId != null) {
if (forClientId.length() != 0) {
UIComponent result = RendererUtils.getInstance().findComponentFor(component, forClientId);
if (result == null) {
msgIter = Iterators.emptyIterator();
} else {
String clientId = result.getClientId(context);
msgIter = getMessagesForId(context, clientId);
}
} else {
msgIter = getMessagesForId(context, null);
}
} else {
msgIter = Iterators.emptyIterator();
Iterator<String> clientIdsWithMessages = context.getClientIdsWithMessages();
while (clientIdsWithMessages.hasNext()) {
String clientId = (String) clientIdsWithMessages.next();
msgIter = Iterators.concat(msgIter, getMessagesForId(context, clientId));
}
}
return msgIter;
}
private void appendScanRow(StringBuilder buf, Bound bound) {
ScanRanges scanRanges = context.getScanRanges();
KeyRange minMaxRange = context.getMinMaxRange();
Iterator<byte[]> minMaxIterator = Iterators.emptyIterator();
if (minMaxRange != null) {
RowKeySchema schema = tableRef.getTable().getRowKeySchema();
if (!minMaxRange.isUnbound(bound)) {
minMaxIterator = new RowKeyValueIterator(schema, minMaxRange.getRange(bound));
}
}
int nRanges = scanRanges.getRanges().size();
for (int i = 0, minPos = 0; minPos < nRanges || minMaxIterator.hasNext(); i++) {
List<KeyRange> ranges = minPos >= nRanges ? EVERYTHING : scanRanges.getRanges().get(minPos++);
KeyRange range = bound == Bound.LOWER ? ranges.get(0) : ranges.get(ranges.size() - 1);
byte[] b = range.getRange(bound);
Boolean isNull =
KeyRange.IS_NULL_RANGE == range
? Boolean.TRUE
: KeyRange.IS_NOT_NULL_RANGE == range ? Boolean.FALSE : null;
if (minMaxIterator.hasNext()) {
byte[] bMinMax = minMaxIterator.next();
int cmp = Bytes.compareTo(bMinMax, b) * (bound == Bound.LOWER ? 1 : -1);
if (cmp > 0) {
minPos = nRanges;
b = bMinMax;
isNull = null;
} else if (cmp < 0) {
minMaxIterator = Iterators.emptyIterator();
}
}
appendPKColumnValue(buf, b, isNull, i);
buf.append(',');
}
}
@Override
public Iterator<JobData> iterator() {
if (jobs == null) {
return Iterators.emptyIterator();
}
return jobs.iterator();
}
public Iterator<RangeTombstone> getRangeTombstoneIterator(final ColumnFamily source) {
final DeletionInfo delInfo = source.deletionInfo();
if (!delInfo.hasRanges() || slices.length == 0) return Iterators.emptyIterator();
return new AbstractIterator<RangeTombstone>() {
private int sliceIdx = 0;
private Iterator<RangeTombstone> sliceIter = currentRangeIter();
protected RangeTombstone computeNext() {
while (true) {
if (sliceIter.hasNext()) return sliceIter.next();
if (!nextSlice()) return endOfData();
sliceIter = currentRangeIter();
}
}
private Iterator<RangeTombstone> currentRangeIter() {
ColumnSlice slice = slices[reversed ? (slices.length - 1 - sliceIdx) : sliceIdx];
return reversed
? delInfo.rangeIterator(slice.finish, slice.start)
: delInfo.rangeIterator(slice.start, slice.finish);
}
private boolean nextSlice() {
return ++sliceIdx < slices.length;
}
};
}
/**
* Returns a valid instance selection for the current selection of the tree viewer. Returns <code>
* null</code> if there is none.
*
* @return a valid instance selection for the current selection of the tree viewer or <code>null
* </code>
*/
private InstanceSelection getValidSelection() {
ISelection viewerSelection = treeViewer.getSelection();
if (!(viewerSelection instanceof ITreeSelection) || viewerSelection.isEmpty()) return null;
ITreeSelection treeSelection = (ITreeSelection) treeViewer.getSelection();
TreePath firstPath = treeSelection.getPaths()[0]; // XXX use all paths
// instead of first
// only?
InstanceValidationMessage firstMessage;
Iterator<InstanceValidationMessage> restIter;
if (firstPath.getLastSegment() instanceof InstanceValidationMessage) {
firstMessage = (InstanceValidationMessage) firstPath.getLastSegment();
restIter = Iterators.emptyIterator();
} else {
Collection<InstanceValidationMessage> messages =
contentProvider.getMessages(treeSelection.getPaths()[0]);
if (messages.isEmpty()) return null; // shouldn't happen, but doesn't really matter
restIter = messages.iterator();
firstMessage = restIter.next();
}
InstanceService is = PlatformUI.getWorkbench().getService(InstanceService.class);
// check first message for valid instance reference
if (firstMessage.getInstanceReference() == null
|| is.getInstance(firstMessage.getInstanceReference()) == null) return null;
Set<InstanceReference> references = new HashSet<InstanceReference>();
references.add(firstMessage.getInstanceReference());
while (restIter.hasNext()) references.add(restIter.next().getInstanceReference());
return new DefaultInstanceSelection(references.toArray());
}
@Override
public Iterator<? extends T> iterator(long first, long count) {
Collection<T> data = dataModel.getObject();
if (data == null || data.size() == 0) return Iterators.emptyIterator();
Iterator<T> it;
final SortParam<S> sortParam = getSort();
if (sortParam != null && sortParam.getProperty() != null) {
Ordering<T> ordering =
Ordering.natural()
.nullsFirst()
.onResultOf(
new Function<T, Comparable<?>>() {
@Override
public Comparable<?> apply(T input) {
return comparableValue(input, sortParam.getProperty());
}
});
if (!sortParam.isAscending()) ordering = ordering.reverse();
it = ordering.sortedCopy(data).iterator();
} else {
it = data.iterator();
}
if (first > 0) Iterators.advance(it, (int) first);
return count >= 0 ? Iterators.limit(it, (int) count) : it;
}
@Override
public Iterator<byte[]> iterator() {
if (isEmpty()) {
return Iterators.emptyIterator();
}
return Iterators.transform(entries.iterator(), ENTRY_TO_BYTE_ARRAY);
}
private Iterator<Pair<byte[], List<Mutation>>> addRowMutations(
final TableRef tableRef,
final Map<ImmutableBytesPtr, Map<PColumn, byte[]>> values,
long timestamp,
boolean includeMutableIndexes) {
final List<Mutation> mutations = Lists.newArrayListWithExpectedSize(values.size());
Iterator<Map.Entry<ImmutableBytesPtr, Map<PColumn, byte[]>>> iterator =
values.entrySet().iterator();
while (iterator.hasNext()) {
Map.Entry<ImmutableBytesPtr, Map<PColumn, byte[]>> rowEntry = iterator.next();
ImmutableBytesPtr key = rowEntry.getKey();
PRow row = tableRef.getTable().newRow(connection.getKeyValueBuilder(), timestamp, key);
if (rowEntry.getValue() == PRow.DELETE_MARKER) { // means delete
row.delete();
} else {
for (Map.Entry<PColumn, byte[]> valueEntry : rowEntry.getValue().entrySet()) {
row.setValue(valueEntry.getKey(), valueEntry.getValue());
}
}
mutations.addAll(row.toRowMutations());
}
final Iterator<PTable>
indexes = // Only maintain tables with immutable rows through this client-side mechanism
(tableRef.getTable().isImmutableRows() || includeMutableIndexes)
? IndexMaintainer.nonDisabledIndexIterator(
tableRef.getTable().getIndexes().iterator())
: Iterators.<PTable>emptyIterator();
return new Iterator<Pair<byte[], List<Mutation>>>() {
boolean isFirst = true;
@Override
public boolean hasNext() {
return isFirst || indexes.hasNext();
}
@Override
public Pair<byte[], List<Mutation>> next() {
if (isFirst) {
isFirst = false;
return new Pair<byte[], List<Mutation>>(
tableRef.getTable().getPhysicalName().getBytes(), mutations);
}
PTable index = indexes.next();
List<Mutation> indexMutations;
try {
indexMutations =
IndexUtil.generateIndexData(
tableRef.getTable(), index, mutations, tempPtr, connection.getKeyValueBuilder());
} catch (SQLException e) {
throw new IllegalDataException(e);
}
return new Pair<byte[], List<Mutation>>(index.getPhysicalName().getBytes(), indexMutations);
}
@Override
public void remove() {
throw new UnsupportedOperationException();
}
};
}
@Override
public Iterator<Expression> visitEnter(ScalarFunction node) {
return node.preservesOrder() == OrderPreserving.NO
? Iterators.<Expression>emptyIterator()
: Iterators.singletonIterator(
node.getChildren().get(node.getKeyFormationTraversalIndex()));
}
/**
* iterator over the Tokens in the given ring, starting with the token for the node owning start
* (which does not have to be a Token in the ring)
*
* @param includeMin True if the minimum token should be returned in the ring even if it has no
* owner.
*/
public static Iterator<Token> ringIterator(
final ArrayList<Token> ring, Token start, boolean includeMin) {
if (ring.isEmpty())
return includeMin
? Iterators.singletonIterator(StorageService.getPartitioner().getMinimumToken())
: Iterators.<Token>emptyIterator();
final boolean insertMin = includeMin && !ring.get(0).isMinimum();
final int startIndex = firstTokenIndex(ring, start, insertMin);
return new AbstractIterator<Token>() {
int j = startIndex;
protected Token computeNext() {
if (j < -1) return endOfData();
try {
// return minimum for index == -1
if (j == -1) return StorageService.getPartitioner().getMinimumToken();
// return ring token for other indexes
return ring.get(j);
} finally {
j++;
if (j == ring.size()) j = insertMin ? -1 : 0;
if (j == startIndex)
// end iteration
j = -2;
}
}
};
}
@Override
protected Iterator<File> resolveFiles(final URI fileURI) {
if (fileURI.getScheme() != null
&& fileURI.getScheme().equals("file")
&& new File(fileURI).exists()) {
return Iterators.singletonIterator(new File(fileURI));
}
if (fileURI.toString().startsWith(PREFIX)) {
String path = fileURI.toString().substring(PREFIX_LENGTH);
final String realPath = this.servletContext.getRealPath(path);
if (realPath == null) {
return Iterators.emptyIterator();
}
return Iterators.singletonIterator(new File(realPath));
}
return Iterators.emptyIterator();
}
/**
* Gets an iterator for the time-series stored under the given field name. This iterates over the
* time-series in the same order as they were added.
*
* @param field the data field, not null
* @return an iterator, not null
*/
public Iterator<HistoricalTimeSeries> iterator(final String field) {
ArgumentChecker.notNull(field, "field");
final Entry e = _data.get(field);
if (e == null) {
return Iterators.emptyIterator();
}
return e.iterator();
}
@Override
public Iterator<Edge<I, E>> iterator() {
if (edgeCount == 0) {
return Iterators.emptyIterator();
} else {
return new ByteArrayEdgeIterator();
}
}
@Override
public Iterator<Tree> childrenIterator() {
return Iterators.<Tree>concat(
Iterators.<Tree>forArray(
ifKeyword, openParenToken, condition, closeParenToken, thenStatement),
elseKeyword != null
? Iterators.<Tree>forArray(elseKeyword, elseStatement)
: Iterators.<Tree>emptyIterator());
}
public void testNullPointers() throws Exception {
NullPointerTester tester = new NullPointerTester();
tester.setDefault(Comparator.class, Ordering.natural());
tester.setDefault(Comparable.class, "");
tester.setDefault(Iterator.class, Iterators.emptyIterator());
tester.setDefault(Iterable.class, Collections.emptySet());
tester.setDefault(Comparable[].class, new Comparable[0]);
tester.testAllPublicStaticMethods(ImmutableSortedMultiset.class);
}
public static Iterator<Filter> getFilterIterator(Scan scan) {
Iterator<Filter> filterIterator;
Filter topLevelFilter = scan.getFilter();
if (topLevelFilter == null) {
filterIterator = Iterators.emptyIterator();
} else if (topLevelFilter instanceof FilterList) {
filterIterator = ((FilterList) topLevelFilter).getFilters().iterator();
} else {
filterIterator = Iterators.singletonIterator(topLevelFilter);
}
return filterIterator;
}
public Iterator<RangeTombstone> getRangeTombstoneIterator(final ColumnFamily source) {
if (!source.deletionInfo().hasRanges()) return Iterators.<RangeTombstone>emptyIterator();
return new AbstractIterator<RangeTombstone>() {
private final Iterator<CellName> names = columns.iterator();
private RangeTombstone lastFindRange;
protected RangeTombstone computeNext() {
while (names.hasNext()) {
CellName next = names.next();
if (lastFindRange != null && lastFindRange.includes(source.getComparator(), next))
return lastFindRange;
// We keep the last range around as since names are in sort order, it's
// possible it will match the next name too.
lastFindRange = source.deletionInfo().rangeCovering(next);
if (lastFindRange != null) return lastFindRange;
}
return endOfData();
}
};
}
public Iterator<Pair<byte[], List<Mutation>>> toMutations(final boolean includeMutableIndexes) {
final Iterator<Map.Entry<TableRef, Map<ImmutableBytesPtr, Map<PColumn, byte[]>>>> iterator =
this.mutations.entrySet().iterator();
if (!iterator.hasNext()) {
return Iterators.emptyIterator();
}
Long scn = connection.getSCN();
final long timestamp = scn == null ? HConstants.LATEST_TIMESTAMP : scn;
return new Iterator<Pair<byte[], List<Mutation>>>() {
private Map.Entry<TableRef, Map<ImmutableBytesPtr, Map<PColumn, byte[]>>> current =
iterator.next();
private Iterator<Pair<byte[], List<Mutation>>> innerIterator = init();
private Iterator<Pair<byte[], List<Mutation>>> init() {
return addRowMutations(
current.getKey(), current.getValue(), timestamp, includeMutableIndexes);
}
@Override
public boolean hasNext() {
return innerIterator.hasNext() || iterator.hasNext();
}
@Override
public Pair<byte[], List<Mutation>> next() {
if (!innerIterator.hasNext()) {
current = iterator.next();
}
return innerIterator.next();
}
@Override
public void remove() {
throw new UnsupportedOperationException();
}
};
}
@Override
public Iterator<Feature> iterator() {
Iterator<Ref> featureRefs = Iterators.emptyIterator();
GeoGIT ggit = new GeoGIT(repository);
VersionQuery versionQuery = new VersionQuery(ggit, featureType.getName());
try {
for (ResourceId rid : resourceIds) {
Iterator<Ref> ridIterator;
ridIterator = versionQuery.get(rid);
featureRefs = Iterators.concat(featureRefs, ridIterator);
}
} catch (Exception e) {
throw new RuntimeException(e);
}
featureRefs = versionQuery.filterByQueryVersion(featureRefs, query);
Iterator<Feature> features =
Iterators.transform(featureRefs, new RefToFeature(repository, featureType));
return features;
}
private QueuedEntityPlacingIterator(Iterator<Object> entityIterator) {
this.entityIterator = entityIterator;
moveSelectorIterator = Iterators.emptyIterator();
}
@Nonnull
@Override
public Iterator<String> getParameterNames(@Nullable DexReader reader) {
return Iterators.emptyIterator();
}
@Nonnull
@Override
public Iterator<DebugItem> iterator() {
return Iterators.emptyIterator();
}
public Iterator<E> iterator() {
return Iterators.emptyIterator();
}
{
val$inputs = iterator;
super();
current = Iterators.emptyIterator();
}
public UnmodifiableIterator<Object> iterator() {
return Iterators.emptyIterator();
}
@Override
public Iterator<TitanProperty> propertyIterator() {
return Iterators.emptyIterator();
}
@Override
public Iterator<TitanEdge> edgeIterator() {
return Iterators.emptyIterator();
}
public MutationState createTable(CreateTableStatement statement, byte[][] splits)
throws SQLException {
PTableType tableType = statement.getTableType();
boolean isView = tableType == PTableType.VIEW;
if (isView && !statement.getProps().isEmpty()) {
throw new SQLExceptionInfo.Builder(SQLExceptionCode.VIEW_WITH_TABLE_CONFIG)
.build()
.buildException();
}
connection.rollback();
boolean wasAutoCommit = connection.getAutoCommit();
try {
connection.setAutoCommit(false);
TableName tableNameNode = statement.getTableName();
String schemaName = tableNameNode.getSchemaName();
String tableName = tableNameNode.getTableName();
PrimaryKeyConstraint pkConstraint = statement.getPrimaryKeyConstraint();
String pkName = null;
Set<String> pkColumns = Collections.<String>emptySet();
Iterator<String> pkColumnsIterator = Iterators.emptyIterator();
if (pkConstraint != null) {
pkColumns = pkConstraint.getColumnNames();
pkColumnsIterator = pkColumns.iterator();
pkName = pkConstraint.getName();
}
List<ColumnDef> colDefs = statement.getColumnDefs();
List<PColumn> columns = Lists.newArrayListWithExpectedSize(colDefs.size());
PreparedStatement colUpsert = connection.prepareStatement(INSERT_COLUMN);
int columnOrdinal = 0;
Map<String, PName> familyNames = Maps.newLinkedHashMap();
boolean isPK = false;
for (ColumnDef colDef : colDefs) {
if (colDef.isPK()) {
if (isPK) {
throw new SQLExceptionInfo.Builder(SQLExceptionCode.PRIMARY_KEY_ALREADY_EXISTS)
.setColumnName(colDef.getColumnDefName().getColumnName().getName())
.build()
.buildException();
}
isPK = true;
}
PColumn column = newColumn(columnOrdinal++, colDef, pkConstraint);
if (SchemaUtil.isPKColumn(column)) {
// TODO: remove this constraint?
if (!pkColumns.isEmpty()
&& !column.getName().getString().equals(pkColumnsIterator.next())) {
throw new SQLExceptionInfo.Builder(SQLExceptionCode.PRIMARY_KEY_OUT_OF_ORDER)
.setSchemaName(schemaName)
.setTableName(tableName)
.setColumnName(column.getName().getString())
.build()
.buildException();
}
}
columns.add(column);
if (colDef.getDataType() == PDataType.BINARY && colDefs.size() > 1) {
throw new SQLExceptionInfo.Builder(SQLExceptionCode.BINARY_IN_ROW_KEY)
.setSchemaName(schemaName)
.setTableName(tableName)
.setColumnName(column.getName().getString())
.build()
.buildException();
}
if (column.getFamilyName() != null) {
familyNames.put(column.getFamilyName().getString(), column.getFamilyName());
}
}
if (!isPK && pkColumns.isEmpty()) {
throw new SQLExceptionInfo.Builder(SQLExceptionCode.PRIMARY_KEY_MISSING)
.setSchemaName(schemaName)
.setTableName(tableName)
.build()
.buildException();
}
List<Pair<byte[], Map<String, Object>>> familyPropList =
Lists.newArrayListWithExpectedSize(familyNames.size());
Map<String, Object> commonFamilyProps = Collections.emptyMap();
Map<String, Object> tableProps = Collections.emptyMap();
if (!statement.getProps().isEmpty()) {
if (statement.isView()) {
throw new SQLExceptionInfo.Builder(SQLExceptionCode.VIEW_WITH_PROPERTIES)
.build()
.buildException();
}
for (String familyName : statement.getProps().keySet()) {
if (!familyName.equals(QueryConstants.ALL_FAMILY_PROPERTIES_KEY)) {
if (familyNames.get(familyName) == null) {
throw new SQLExceptionInfo.Builder(SQLExceptionCode.PROPERTIES_FOR_FAMILY)
.setFamilyName(familyName)
.build()
.buildException();
}
}
}
commonFamilyProps = Maps.newHashMapWithExpectedSize(statement.getProps().size());
tableProps = Maps.newHashMapWithExpectedSize(statement.getProps().size());
Collection<Pair<String, Object>> props =
statement.getProps().get(QueryConstants.ALL_FAMILY_PROPERTIES_KEY);
// Somewhat hacky way of determining if property is for HColumnDescriptor or
// HTableDescriptor
HColumnDescriptor defaultDescriptor =
new HColumnDescriptor(QueryConstants.DEFAULT_COLUMN_FAMILY_BYTES);
for (Pair<String, Object> prop : props) {
if (defaultDescriptor.getValue(prop.getFirst()) != null) {
commonFamilyProps.put(prop.getFirst(), prop.getSecond());
} else {
tableProps.put(prop.getFirst(), prop.getSecond());
}
}
}
for (PName familyName : familyNames.values()) {
Collection<Pair<String, Object>> props = statement.getProps().get(familyName.getString());
if (props.isEmpty()) {
familyPropList.add(
new Pair<byte[], Map<String, Object>>(familyName.getBytes(), commonFamilyProps));
} else {
Map<String, Object> combinedFamilyProps =
Maps.newHashMapWithExpectedSize(props.size() + commonFamilyProps.size());
combinedFamilyProps.putAll(commonFamilyProps);
for (Pair<String, Object> prop : props) {
combinedFamilyProps.put(prop.getFirst(), prop.getSecond());
}
familyPropList.add(
new Pair<byte[], Map<String, Object>>(familyName.getBytes(), combinedFamilyProps));
}
}
// Bootstrapping for our SYSTEM.TABLE that creates itself before it exists
if (tableType == PTableType.SYSTEM) {
PTable table =
new PTableImpl(
new PNameImpl(tableName),
tableType,
MetaDataProtocol.MIN_TABLE_TIMESTAMP,
0,
QueryConstants.SYSTEM_TABLE_PK_NAME,
null,
columns);
connection.addTable(schemaName, table);
}
for (PColumn column : columns) {
addColumnMutation(schemaName, tableName, column, colUpsert);
}
Integer saltBucketNum = (Integer) tableProps.remove(PhoenixDatabaseMetaData.SALT_BUCKETS);
if (saltBucketNum != null
&& (saltBucketNum <= 0 || saltBucketNum > SaltingUtil.MAX_BUCKET_NUM)) {
throw new SQLExceptionInfo.Builder(SQLExceptionCode.INVALID_BUCKET_NUM)
.build()
.buildException();
}
PreparedStatement tableUpsert = connection.prepareStatement(CREATE_TABLE);
tableUpsert.setString(1, schemaName);
tableUpsert.setString(2, tableName);
tableUpsert.setString(3, tableType.getSerializedValue());
tableUpsert.setInt(4, 0);
tableUpsert.setInt(5, columnOrdinal);
if (saltBucketNum != null) {
tableUpsert.setInt(6, saltBucketNum);
} else {
tableUpsert.setNull(6, Types.INTEGER);
}
tableUpsert.setString(7, pkName);
tableUpsert.execute();
final List<Mutation> tableMetaData = connection.getMutationState().toMutations();
connection.rollback();
MetaDataMutationResult result =
connection
.getQueryServices()
.createTable(tableMetaData, isView, tableProps, familyPropList, splits);
MutationCode code = result.getMutationCode();
switch (code) {
case TABLE_ALREADY_EXISTS:
connection.addTable(schemaName, result.getTable());
if (!statement.ifNotExists()) {
throw new TableAlreadyExistsException(schemaName, tableName);
}
break;
case NEWER_TABLE_FOUND:
// TODO: add table if in result?
throw new NewerTableAlreadyExistsException(schemaName, tableName);
case UNALLOWED_TABLE_MUTATION:
throw new SQLExceptionInfo.Builder(SQLExceptionCode.CANNOT_MUTATE_TABLE)
.setSchemaName(schemaName)
.setTableName(tableName)
.build()
.buildException();
default:
PTable table =
new PTableImpl(
new PNameImpl(tableName),
tableType,
result.getMutationTime(),
0,
pkName,
saltBucketNum,
columns);
connection.addTable(schemaName, table);
if (tableType == PTableType.USER) {
connection.setAutoCommit(true);
// Delete everything in the column. You'll still be able to do queries at earlier
// timestamps
Long scn = connection.getSCN();
long ts = (scn == null ? result.getMutationTime() : scn);
PSchema schema =
new PSchemaImpl(
schemaName,
ImmutableMap.<String, PTable>of(table.getName().getString(), table));
TableRef tableRef = new TableRef(null, table, schema, ts);
byte[] emptyCF = SchemaUtil.getEmptyColumnFamily(table.getColumnFamilies());
MutationPlan plan =
new PostDDLCompiler(connection).compile(tableRef, emptyCF, null, ts);
return connection.getQueryServices().updateData(plan);
}
break;
}
return new MutationState(0, connection);
} finally {
connection.setAutoCommit(wasAutoCommit);
}
}
public void testCopyOf_iterator_empty() {
Iterator<String> iterator = Iterators.emptyIterator();
List<String> list = ImmutableList.copyOf(iterator);
assertEquals(Collections.emptyList(), list);
}
@Override
public Iterator<TitanRelation> relationIterator() {
return Iterators.emptyIterator();
}