/*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package com.facebook.presto.sql.rewrite;
import com.facebook.presto.Session;
import com.facebook.presto.connector.ConnectorId;
import com.facebook.presto.metadata.FunctionKind;
import com.facebook.presto.metadata.Metadata;
import com.facebook.presto.metadata.QualifiedObjectName;
import com.facebook.presto.metadata.SessionPropertyManager.SessionPropertyValue;
import com.facebook.presto.metadata.SqlFunction;
import com.facebook.presto.metadata.TableHandle;
import com.facebook.presto.metadata.TableLayout;
import com.facebook.presto.metadata.TableLayoutResult;
import com.facebook.presto.metadata.ViewDefinition;
import com.facebook.presto.security.AccessControl;
import com.facebook.presto.spi.CatalogSchemaName;
import com.facebook.presto.spi.ColumnHandle;
import com.facebook.presto.spi.ColumnMetadata;
import com.facebook.presto.spi.ConnectorTableMetadata;
import com.facebook.presto.spi.Constraint;
import com.facebook.presto.spi.PrestoException;
import com.facebook.presto.spi.SchemaTableName;
import com.facebook.presto.spi.session.PropertyMetadata;
import com.facebook.presto.sql.analyzer.QueryExplainer;
import com.facebook.presto.sql.analyzer.SemanticException;
import com.facebook.presto.sql.parser.ParsingException;
import com.facebook.presto.sql.parser.SqlParser;
import com.facebook.presto.sql.tree.AllColumns;
import com.facebook.presto.sql.tree.ArrayConstructor;
import com.facebook.presto.sql.tree.AstVisitor;
import com.facebook.presto.sql.tree.BooleanLiteral;
import com.facebook.presto.sql.tree.Cast;
import com.facebook.presto.sql.tree.ColumnDefinition;
import com.facebook.presto.sql.tree.CreateTable;
import com.facebook.presto.sql.tree.CreateView;
import com.facebook.presto.sql.tree.DoubleLiteral;
import com.facebook.presto.sql.tree.Explain;
import com.facebook.presto.sql.tree.Expression;
import com.facebook.presto.sql.tree.GroupBy;
import com.facebook.presto.sql.tree.LikePredicate;
import com.facebook.presto.sql.tree.LongLiteral;
import com.facebook.presto.sql.tree.Node;
import com.facebook.presto.sql.tree.OrderBy;
import com.facebook.presto.sql.tree.QualifiedName;
import com.facebook.presto.sql.tree.Query;
import com.facebook.presto.sql.tree.Relation;
import com.facebook.presto.sql.tree.SelectItem;
import com.facebook.presto.sql.tree.ShowCatalogs;
import com.facebook.presto.sql.tree.ShowColumns;
import com.facebook.presto.sql.tree.ShowCreate;
import com.facebook.presto.sql.tree.ShowFunctions;
import com.facebook.presto.sql.tree.ShowGrants;
import com.facebook.presto.sql.tree.ShowPartitions;
import com.facebook.presto.sql.tree.ShowSchemas;
import com.facebook.presto.sql.tree.ShowSession;
import com.facebook.presto.sql.tree.ShowTables;
import com.facebook.presto.sql.tree.SimpleGroupBy;
import com.facebook.presto.sql.tree.SingleColumn;
import com.facebook.presto.sql.tree.SortItem;
import com.facebook.presto.sql.tree.Statement;
import com.facebook.presto.sql.tree.StringLiteral;
import com.facebook.presto.sql.tree.TableElement;
import com.facebook.presto.sql.tree.Values;
import com.google.common.base.Joiner;
import com.google.common.collect.ImmutableList;
import com.google.common.collect.ImmutableMap;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
import java.util.Optional;
import java.util.Set;
import java.util.SortedMap;
import static com.facebook.presto.connector.informationSchema.InformationSchemaMetadata.TABLE_COLUMNS;
import static com.facebook.presto.connector.informationSchema.InformationSchemaMetadata.TABLE_INTERNAL_PARTITIONS;
import static com.facebook.presto.connector.informationSchema.InformationSchemaMetadata.TABLE_SCHEMATA;
import static com.facebook.presto.connector.informationSchema.InformationSchemaMetadata.TABLE_TABLES;
import static com.facebook.presto.connector.informationSchema.InformationSchemaMetadata.TABLE_TABLE_PRIVILEGES;
import static com.facebook.presto.metadata.MetadataListing.listCatalogs;
import static com.facebook.presto.metadata.MetadataListing.listSchemas;
import static com.facebook.presto.metadata.MetadataUtil.createCatalogSchemaName;
import static com.facebook.presto.metadata.MetadataUtil.createQualifiedName;
import static com.facebook.presto.metadata.MetadataUtil.createQualifiedObjectName;
import static com.facebook.presto.spi.StandardErrorCode.INVALID_TABLE_PROPERTY;
import static com.facebook.presto.sql.QueryUtil.aliased;
import static com.facebook.presto.sql.QueryUtil.aliasedName;
import static com.facebook.presto.sql.QueryUtil.aliasedNullToEmpty;
import static com.facebook.presto.sql.QueryUtil.ascending;
import static com.facebook.presto.sql.QueryUtil.caseWhen;
import static com.facebook.presto.sql.QueryUtil.equal;
import static com.facebook.presto.sql.QueryUtil.functionCall;
import static com.facebook.presto.sql.QueryUtil.identifier;
import static com.facebook.presto.sql.QueryUtil.logicalAnd;
import static com.facebook.presto.sql.QueryUtil.ordering;
import static com.facebook.presto.sql.QueryUtil.row;
import static com.facebook.presto.sql.QueryUtil.selectAll;
import static com.facebook.presto.sql.QueryUtil.selectList;
import static com.facebook.presto.sql.QueryUtil.simpleQuery;
import static com.facebook.presto.sql.QueryUtil.singleValueQuery;
import static com.facebook.presto.sql.QueryUtil.subquery;
import static com.facebook.presto.sql.QueryUtil.table;
import static com.facebook.presto.sql.QueryUtil.unaliasedName;
import static com.facebook.presto.sql.SqlFormatter.formatSql;
import static com.facebook.presto.sql.analyzer.SemanticErrorCode.CATALOG_NOT_SPECIFIED;
import static com.facebook.presto.sql.analyzer.SemanticErrorCode.MISSING_SCHEMA;
import static com.facebook.presto.sql.analyzer.SemanticErrorCode.MISSING_TABLE;
import static com.facebook.presto.sql.analyzer.SemanticErrorCode.NOT_SUPPORTED;
import static com.facebook.presto.sql.analyzer.SemanticErrorCode.VIEW_PARSE_ERROR;
import static com.facebook.presto.sql.tree.BooleanLiteral.FALSE_LITERAL;
import static com.facebook.presto.sql.tree.BooleanLiteral.TRUE_LITERAL;
import static com.facebook.presto.sql.tree.ShowCreate.Type.TABLE;
import static com.facebook.presto.sql.tree.ShowCreate.Type.VIEW;
import static com.google.common.base.Strings.nullToEmpty;
import static com.google.common.collect.ImmutableList.toImmutableList;
import static com.google.common.collect.Iterables.getOnlyElement;
import static java.lang.String.format;
import static java.util.Objects.requireNonNull;
import static java.util.stream.Collectors.toList;
final class ShowQueriesRewrite
implements StatementRewrite.Rewrite
{
@Override
public Statement rewrite(
Session session,
Metadata metadata,
SqlParser parser,
Optional<QueryExplainer> queryExplainer,
Statement node,
List<Expression> parameters,
AccessControl accessControl)
{
return (Statement) new Visitor(metadata, parser, session, parameters, accessControl).process(node, null);
}
private static class Visitor
extends AstVisitor<Node, Void>
{
private final Metadata metadata;
private final Session session;
private final SqlParser sqlParser;
List<Expression> parameters;
private final AccessControl accessControl;
public Visitor(Metadata metadata, SqlParser sqlParser, Session session, List<Expression> parameters, AccessControl accessControl)
{
this.metadata = requireNonNull(metadata, "metadata is null");
this.sqlParser = requireNonNull(sqlParser, "sqlParser is null");
this.session = requireNonNull(session, "session is null");
this.parameters = requireNonNull(parameters, "parameters is null");
this.accessControl = requireNonNull(accessControl, "accessControl is null");
}
@Override
protected Node visitExplain(Explain node, Void context)
{
Statement statement = (Statement) process(node.getStatement(), null);
return new Explain(
node.getLocation().get(),
node.isAnalyze(),
statement,
node.getOptions());
}
@Override
protected Node visitShowTables(ShowTables showTables, Void context)
{
CatalogSchemaName schema = createCatalogSchemaName(session, showTables, showTables.getSchema());
accessControl.checkCanShowTablesMetadata(session.getRequiredTransactionId(), session.getIdentity(), schema);
if (!metadata.schemaExists(session, schema)) {
throw new SemanticException(MISSING_SCHEMA, showTables, "Schema '%s' does not exist", schema.getSchemaName());
}
Expression predicate = equal(identifier("table_schema"), new StringLiteral(schema.getSchemaName()));
Optional<String> likePattern = showTables.getLikePattern();
if (likePattern.isPresent()) {
Expression likePredicate = new LikePredicate(identifier("table_name"), new StringLiteral(likePattern.get()), null);
predicate = logicalAnd(predicate, likePredicate);
}
return simpleQuery(
selectList(aliasedName("table_name", "Table")),
from(schema.getCatalogName(), TABLE_TABLES),
predicate,
ordering(ascending("table_name")));
}
@Override
protected Node visitShowGrants(ShowGrants showGrants, Void context)
{
String catalogName = session.getCatalog().orElse(null);
Optional<Expression> predicate = Optional.empty();
Optional<QualifiedName> tableName = showGrants.getTableName();
if (tableName.isPresent()) {
QualifiedObjectName qualifiedTableName = createQualifiedObjectName(session, showGrants, tableName.get());
if (!metadata.getView(session, qualifiedTableName).isPresent() &&
!metadata.getTableHandle(session, qualifiedTableName).isPresent()) {
throw new SemanticException(MISSING_TABLE, showGrants, "Table '%s' does not exist", tableName);
}
catalogName = qualifiedTableName.getCatalogName();
accessControl.checkCanShowTablesMetadata(
session.getRequiredTransactionId(),
session.getIdentity(),
new CatalogSchemaName(catalogName, qualifiedTableName.getSchemaName()));
predicate = Optional.of(equal(identifier("table_name"), new StringLiteral(qualifiedTableName.getObjectName())));
}
if (catalogName == null) {
throw new SemanticException(CATALOG_NOT_SPECIFIED, showGrants, "Catalog must be specified when session catalog is not set");
}
Set<String> allowedSchemas = listSchemas(session, metadata, accessControl, catalogName);
for (String schema : allowedSchemas) {
accessControl.checkCanShowTablesMetadata(session.getRequiredTransactionId(), session.getIdentity(), new CatalogSchemaName(catalogName, schema));
}
return simpleQuery(
selectList(
aliasedName("grantee", "Grantee"),
aliasedName("table_catalog", "Catalog"),
aliasedName("table_schema", "Schema"),
aliasedName("table_name", "Table"),
aliasedName("privilege_type", "Privilege"),
aliasedName("is_grantable", "Grantable")),
from(catalogName, TABLE_TABLE_PRIVILEGES),
predicate,
Optional.of(ordering(ascending("grantee"), ascending("table_name"))));
}
@Override
protected Node visitShowSchemas(ShowSchemas node, Void context)
{
if (!node.getCatalog().isPresent() && !session.getCatalog().isPresent()) {
throw new SemanticException(CATALOG_NOT_SPECIFIED, node, "Catalog must be specified when session catalog is not set");
}
String catalog = node.getCatalog().orElseGet(() -> session.getCatalog().get());
accessControl.checkCanShowSchemas(session.getRequiredTransactionId(), session.getIdentity(), catalog);
Optional<Expression> predicate = Optional.empty();
Optional<String> likePattern = node.getLikePattern();
if (likePattern.isPresent()) {
predicate = Optional.of(new LikePredicate(identifier("schema_name"), new StringLiteral(likePattern.get()), null));
}
return simpleQuery(
selectList(aliasedName("schema_name", "Schema")),
from(catalog, TABLE_SCHEMATA),
predicate,
Optional.of(ordering(ascending("schema_name"))));
}
@Override
protected Node visitShowCatalogs(ShowCatalogs node, Void context)
{
List<Expression> rows = listCatalogs(session, metadata, accessControl).keySet().stream()
.map(name -> row(new StringLiteral(name)))
.collect(toList());
Optional<Expression> predicate = Optional.empty();
Optional<String> likePattern = node.getLikePattern();
if (likePattern.isPresent()) {
predicate = Optional.of(new LikePredicate(identifier("Catalog"), new StringLiteral(likePattern.get()), null));
}
return simpleQuery(
selectList(new AllColumns()),
aliased(new Values(rows), "catalogs", ImmutableList.of("Catalog")),
predicate,
Optional.of(ordering(ascending("Catalog"))));
}
@Override
protected Node visitShowColumns(ShowColumns showColumns, Void context)
{
QualifiedObjectName tableName = createQualifiedObjectName(session, showColumns, showColumns.getTable());
if (!metadata.getView(session, tableName).isPresent() &&
!metadata.getTableHandle(session, tableName).isPresent()) {
throw new SemanticException(MISSING_TABLE, showColumns, "Table '%s' does not exist", tableName);
}
return simpleQuery(
selectList(
aliasedName("column_name", "Column"),
aliasedName("data_type", "Type"),
aliasedNullToEmpty("extra_info", "Extra"),
aliasedNullToEmpty("comment", "Comment")),
from(tableName.getCatalogName(), TABLE_COLUMNS),
logicalAnd(
equal(identifier("table_schema"), new StringLiteral(tableName.getSchemaName())),
equal(identifier("table_name"), new StringLiteral(tableName.getObjectName()))),
ordering(ascending("ordinal_position")));
}
private static <T> Expression getExpression(PropertyMetadata<T> property, Object value)
throws PrestoException
{
return toExpression(property.encode(property.getJavaType().cast(value)));
}
private static Expression toExpression(Object value)
throws PrestoException
{
if (value instanceof String) {
return new StringLiteral(value.toString());
}
if (value instanceof Boolean) {
return new BooleanLiteral(value.toString());
}
if (value instanceof Long || value instanceof Integer) {
return new LongLiteral(value.toString());
}
if (value instanceof Double) {
return new DoubleLiteral(value.toString());
}
if (value instanceof List) {
List<?> list = (List<?>) value;
return new ArrayConstructor(list.stream()
.map(Visitor::toExpression)
.collect(toList()));
}
throw new PrestoException(INVALID_TABLE_PROPERTY, format("Failed to convert object of type %s to expression: %s", value.getClass().getName(), value));
}
@Override
protected Node visitShowPartitions(ShowPartitions showPartitions, Void context)
{
QualifiedObjectName table = createQualifiedObjectName(session, showPartitions, showPartitions.getTable());
Optional<TableHandle> tableHandle = metadata.getTableHandle(session, table);
if (!tableHandle.isPresent()) {
throw new SemanticException(MISSING_TABLE, showPartitions, "Table '%s' does not exist", table);
}
List<TableLayoutResult> layouts = metadata.getLayouts(session, tableHandle.get(), Constraint.alwaysTrue(), Optional.empty());
if (layouts.size() != 1) {
throw new SemanticException(NOT_SUPPORTED, showPartitions, "Table does not have exactly one layout: %s", table);
}
TableLayout layout = getOnlyElement(layouts).getLayout();
if (!layout.getDiscretePredicates().isPresent()) {
throw new SemanticException(NOT_SUPPORTED, showPartitions, "Table does not have partition columns: %s", table);
}
List<ColumnHandle> partitionColumns = layout.getDiscretePredicates().get().getColumns();
/*
Generate a dynamic pivot to output one column per partition key.
For example, a table with two partition keys (ds, cluster_name)
would generate the following query:
SELECT
partition_number
, max(CASE WHEN partition_key = 'ds' THEN partition_value END) ds
, max(CASE WHEN partition_key = 'cluster_name' THEN partition_value END) cluster_name
FROM ...
GROUP BY partition_number
The values are also cast to the type of the partition column.
The query is then wrapped to allow custom filtering and ordering.
*/
ImmutableList.Builder<SelectItem> selectList = ImmutableList.builder();
ImmutableList.Builder<SelectItem> wrappedList = ImmutableList.builder();
selectList.add(unaliasedName("partition_number"));
for (ColumnHandle columnHandle : partitionColumns) {
ColumnMetadata column = metadata.getColumnMetadata(session, tableHandle.get(), columnHandle);
Expression key = equal(identifier("partition_key"), new StringLiteral(column.getName()));
Expression value = caseWhen(key, identifier("partition_value"));
value = new Cast(value, column.getType().getTypeSignature().toString());
Expression function = functionCall("max", value);
selectList.add(new SingleColumn(function, column.getName()));
wrappedList.add(unaliasedName(column.getName()));
}
Query query = simpleQuery(
selectAll(selectList.build()),
from(table.getCatalogName(), TABLE_INTERNAL_PARTITIONS),
Optional.of(logicalAnd(
equal(identifier("table_schema"), new StringLiteral(table.getSchemaName())),
equal(identifier("table_name"), new StringLiteral(table.getObjectName())))),
Optional.of(new GroupBy(false, ImmutableList.of(new SimpleGroupBy(ImmutableList.of(identifier("partition_number")))))),
Optional.empty(),
Optional.empty(),
Optional.empty());
return simpleQuery(
selectAll(wrappedList.build()),
subquery(query),
showPartitions.getWhere(),
Optional.empty(),
Optional.empty(),
Optional.of(new OrderBy(ImmutableList.<SortItem>builder()
.addAll(showPartitions.getOrderBy())
.add(ascending("partition_number"))
.build())),
showPartitions.getLimit());
}
@Override
protected Node visitShowCreate(ShowCreate node, Void context)
{
QualifiedObjectName objectName = createQualifiedObjectName(session, node, node.getName());
Optional<ViewDefinition> viewDefinition = metadata.getView(session, objectName);
if (node.getType() == VIEW) {
if (!viewDefinition.isPresent()) {
if (metadata.getTableHandle(session, objectName).isPresent()) {
throw new SemanticException(NOT_SUPPORTED, node, "Relation '%s' is a table, not a view", objectName);
}
throw new SemanticException(MISSING_TABLE, node, "View '%s' does not exist", objectName);
}
Query query = parseView(viewDefinition.get().getOriginalSql(), objectName, node);
String sql = formatSql(new CreateView(createQualifiedName(objectName), query, false), Optional.of(parameters)).trim();
return singleValueQuery("Create View", sql);
}
if (node.getType() == TABLE) {
if (viewDefinition.isPresent()) {
throw new SemanticException(NOT_SUPPORTED, node, "Relation '%s' is a view, not a table", objectName);
}
Optional<TableHandle> tableHandle = metadata.getTableHandle(session, objectName);
if (!tableHandle.isPresent()) {
throw new SemanticException(MISSING_TABLE, node, "Table '%s' does not exist", objectName);
}
ConnectorTableMetadata connectorTableMetadata = metadata.getTableMetadata(session, tableHandle.get()).getMetadata();
List<TableElement> columns = connectorTableMetadata.getColumns().stream()
.filter(column -> !column.isHidden())
.map(column -> new ColumnDefinition(column.getName(), column.getType().getDisplayName(), Optional.ofNullable(column.getComment())))
.collect(toImmutableList());
Map<String, Object> properties = connectorTableMetadata.getProperties();
Map<String, PropertyMetadata<?>> allTableProperties = metadata.getTablePropertyManager().getAllProperties().get(tableHandle.get().getConnectorId());
Map<String, Expression> sqlProperties = new HashMap<>();
for (Map.Entry<String, Object> propertyEntry : properties.entrySet()) {
String propertyName = propertyEntry.getKey();
Object value = propertyEntry.getValue();
if (value == null) {
throw new PrestoException(INVALID_TABLE_PROPERTY, format("Property %s for table %s cannot have a null value", propertyName, objectName));
}
PropertyMetadata<?> property = allTableProperties.get(propertyName);
if (!property.getJavaType().isInstance(value)) {
throw new PrestoException(INVALID_TABLE_PROPERTY, format(
"Property %s for table %s should have value of type %s, not %s",
propertyName,
objectName,
property.getJavaType().getName(),
value.getClass().getName()));
}
Expression sqlExpression = getExpression(property, value);
sqlProperties.put(propertyName, sqlExpression);
}
CreateTable createTable = new CreateTable(
QualifiedName.of(objectName.getCatalogName(), objectName.getSchemaName(), objectName.getObjectName()),
columns,
false,
sqlProperties,
connectorTableMetadata.getComment());
return singleValueQuery("Create Table", formatSql(createTable, Optional.of(parameters)).trim());
}
throw new UnsupportedOperationException("SHOW CREATE only supported for tables and views");
}
@Override
protected Node visitShowFunctions(ShowFunctions node, Void context)
{
ImmutableList.Builder<Expression> rows = ImmutableList.builder();
for (SqlFunction function : metadata.listFunctions()) {
rows.add(row(
new StringLiteral(function.getSignature().getName()),
new StringLiteral(function.getSignature().getReturnType().toString()),
new StringLiteral(Joiner.on(", ").join(function.getSignature().getArgumentTypes())),
new StringLiteral(getFunctionType(function)),
function.isDeterministic() ? TRUE_LITERAL : FALSE_LITERAL,
new StringLiteral(nullToEmpty(function.getDescription()))));
}
Map<String, String> columns = ImmutableMap.<String, String>builder()
.put("function_name", "Function")
.put("return_type", "Return Type")
.put("argument_types", "Argument Types")
.put("function_type", "Function Type")
.put("deterministic", "Deterministic")
.put("description", "Description")
.build();
return simpleQuery(
selectAll(columns.entrySet().stream()
.map(entry -> aliasedName(entry.getKey(), entry.getValue()))
.collect(toImmutableList())),
aliased(new Values(rows.build()), "functions", ImmutableList.copyOf(columns.keySet())),
ordering(
ascending("function_name"),
ascending("return_type"),
ascending("argument_types"),
ascending("function_type")));
}
private static String getFunctionType(SqlFunction function)
{
FunctionKind kind = function.getSignature().getKind();
switch (kind) {
case AGGREGATE:
return "aggregate";
case WINDOW:
return "window";
case SCALAR:
return "scalar";
}
throw new IllegalArgumentException("Unsupported function kind: " + kind);
}
@Override
protected Node visitShowSession(ShowSession node, Void context)
{
ImmutableList.Builder<Expression> rows = ImmutableList.builder();
SortedMap<String, ConnectorId> catalogNames = listCatalogs(session, metadata, accessControl);
List<SessionPropertyValue> sessionProperties = metadata.getSessionPropertyManager().getAllSessionProperties(session, catalogNames);
for (SessionPropertyValue sessionProperty : sessionProperties) {
if (sessionProperty.isHidden()) {
continue;
}
String value = sessionProperty.getValue();
String defaultValue = sessionProperty.getDefaultValue();
rows.add(row(
new StringLiteral(sessionProperty.getFullyQualifiedName()),
new StringLiteral(nullToEmpty(value)),
new StringLiteral(nullToEmpty(defaultValue)),
new StringLiteral(sessionProperty.getType()),
new StringLiteral(sessionProperty.getDescription()),
TRUE_LITERAL));
}
// add bogus row so we can support empty sessions
StringLiteral empty = new StringLiteral("");
rows.add(row(empty, empty, empty, empty, empty, FALSE_LITERAL));
return simpleQuery(
selectList(
aliasedName("name", "Name"),
aliasedName("value", "Value"),
aliasedName("default", "Default"),
aliasedName("type", "Type"),
aliasedName("description", "Description")),
aliased(
new Values(rows.build()),
"session",
ImmutableList.of("name", "value", "default", "type", "description", "include")),
identifier("include"));
}
private Query parseView(String view, QualifiedObjectName name, Node node)
{
try {
Statement statement = sqlParser.createStatement(view);
return (Query) statement;
}
catch (ParsingException e) {
throw new SemanticException(VIEW_PARSE_ERROR, node, "Failed parsing stored view '%s': %s", name, e.getMessage());
}
}
private static Relation from(String catalog, SchemaTableName table)
{
return table(QualifiedName.of(catalog, table.getSchemaName(), table.getTableName()));
}
@Override
protected Node visitNode(Node node, Void context)
{
return node;
}
}
}