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The Apache Cassandra Project develops a highly scalable second-generation distributed database, bringing together Dynamo's fully distributed design and Bigtable's ColumnFamily-based data model.
/*
*
* Licensed to the Apache Software Foundation (ASF) under one
* or more contributor license agreements. See the NOTICE file
* distributed with this work for additional information
* regarding copyright ownership. The ASF licenses this file
* to you 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 org.apache.cassandra.cql3.selection;
import java.util.*;
import java.util.stream.Collectors;
import com.google.common.base.Objects;
import com.google.common.collect.*;
import org.apache.cassandra.config.ColumnDefinition;
import org.apache.cassandra.cql3.ColumnSpecification;
/**
* Separately maintains the ColumnSpecifications and their mappings to underlying
* columns as we may receive null mappings. This occurs where a query result
* includes a column specification which does not map to any particular real
* column, e.g. COUNT queries or where no-arg functions like now() are used
*/
public class SelectionColumnMapping implements SelectionColumns
{
private final ArrayList columnSpecifications;
private final HashMultimap columnMappings;
private SelectionColumnMapping()
{
this.columnSpecifications = new ArrayList<>();
this.columnMappings = HashMultimap.create();
}
protected static SelectionColumnMapping newMapping()
{
return new SelectionColumnMapping();
}
protected static SelectionColumnMapping simpleMapping(Iterable columnDefinitions)
{
SelectionColumnMapping mapping = new SelectionColumnMapping();
for (ColumnDefinition def: columnDefinitions)
mapping.addMapping(def, def);
return mapping;
}
protected SelectionColumnMapping addMapping(ColumnSpecification colSpec, ColumnDefinition column)
{
columnSpecifications.add(colSpec);
// functions without arguments do not map to any column, so don't
// record any mapping in that case
if (column != null)
columnMappings.put(colSpec, column);
return this;
}
protected SelectionColumnMapping addMapping(ColumnSpecification colSpec, Iterable columns)
{
columnSpecifications.add(colSpec);
columnMappings.putAll(colSpec, columns);
return this;
}
public List getColumnSpecifications()
{
// return a mutable copy as we may add extra columns
// for ordering (CASSANDRA-4911 & CASSANDRA-8286)
return Lists.newArrayList(columnSpecifications);
}
public Multimap getMappings()
{
return Multimaps.unmodifiableMultimap(columnMappings);
}
public boolean equals(Object obj)
{
if (obj == null)
return false;
if (!(obj instanceof SelectionColumnMapping))
return false;
SelectionColumns other = (SelectionColumns)obj;
return Objects.equal(columnMappings, other.getMappings())
&& Objects.equal(columnSpecifications, other.getColumnSpecifications());
}
public int hashCode()
{
return Objects.hashCode(columnMappings);
}
public String toString()
{
return columnMappings.asMap()
.entrySet()
.stream()
.map(entry ->
entry.getValue()
.stream()
.map(colDef -> colDef.name.toString())
.collect(Collectors.joining(", ", entry.getKey().name.toString() + ":[", "]")))
.collect(Collectors.joining(", ",
columnSpecifications.stream()
.map(colSpec -> colSpec.name.toString())
.collect(Collectors.joining(", ",
"{ Columns:[",
"], Mappings:{")),
"} }"));
}
}