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/*
 * 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
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 * Unless required by applicable law or agreed to in writing, software
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package org.apache.cassandra.cql3.selection;

import java.nio.ByteBuffer;
import java.util.List;

import org.apache.cassandra.config.CFMetaData;
import org.apache.cassandra.cql3.ColumnIdentifier;
import org.apache.cassandra.cql3.ColumnSpecification;
import org.apache.cassandra.cql3.QueryOptions;
import org.apache.cassandra.cql3.functions.Function;
import org.apache.cassandra.cql3.selection.Selection.ResultSetBuilder;
import org.apache.cassandra.db.marshal.AbstractType;
import org.apache.cassandra.exceptions.InvalidRequestException;
import org.apache.cassandra.transport.ProtocolVersion;

/**
 * A Selector is used to convert the data returned by the storage engine into the data requested by the
 * user. They correspond to the <selector> elements from the select clause.
 * 

Since the introduction of aggregation, Selectors cannot be called anymore by multiple threads * as they have an internal state.

*/ public abstract class Selector { /** * A factory for Selector instances. */ public static abstract class Factory { public void addFunctionsTo(List functions) { } /** * Returns the column specification corresponding to the output value of the selector instances created by * this factory. * * @param cfm the column family meta data * @return a column specification */ public final ColumnSpecification getColumnSpecification(CFMetaData cfm) { return new ColumnSpecification(cfm.ksName, cfm.cfName, new ColumnIdentifier(getColumnName(), true), // note that the name is not necessarily // a true column name so we shouldn't intern it getReturnType()); } /** * Creates a new Selector instance. * * @param options the options of the query for which the instance is created (some selector * depends on the bound values in particular). * @return a new Selector instance */ public abstract Selector newInstance(QueryOptions options) throws InvalidRequestException; /** * Checks if this factory creates selectors instances that creates aggregates. * * @return true if this factory creates selectors instances that creates aggregates, * false otherwise */ public boolean isAggregateSelectorFactory() { return false; } /** * Checks if this factory creates writetime selectors instances. * * @return true if this factory creates writetime selectors instances, * false otherwise */ public boolean isWritetimeSelectorFactory() { return false; } /** * Checks if this factory creates TTL selectors instances. * * @return true if this factory creates TTL selectors instances, * false otherwise */ public boolean isTTLSelectorFactory() { return false; } /** * Checks if this factory creates Selectors that simply return the specified column. * * @param index the column index * @return true if this factory creates Selectors that simply return * the specified column, false otherwise. */ public boolean isSimpleSelectorFactory(int index) { return false; } /** * Returns the name of the column corresponding to the output value of the selector instances created by * this factory. * * @return a column name */ protected abstract String getColumnName(); /** * Returns the name of the column corresponding to the output value of the selector instances created by * this factory that is safe to use directly in CQL queries. * * @return a column name */ protected String getColumnNameCQL3() { return getColumnName(); } /** * Returns the type of the values returned by the selector instances created by this factory. * * @return the selector output type */ protected abstract AbstractType getReturnType(); /** * Record a mapping between the ColumnDefinitions that are used by the selector * instances created by this factory and a column in the ResultSet.Metadata * returned with a query. In most cases, this is likely to be a 1:1 mapping, * but some selector instances may utilise multiple columns (or none at all) * to produce a value (i.e. functions). * * @param mapping the instance of the column mapping belonging to the current query's Selection * @param resultsColumn the column in the ResultSet.Metadata to which the ColumnDefinitions used * by the Selector are to be mapped */ protected abstract void addColumnMapping(SelectionColumnMapping mapping, ColumnSpecification resultsColumn); } /** * Add the current value from the specified ResultSetBuilder. * * @param protocolVersion protocol version used for serialization * @param rs the ResultSetBuilder * @throws InvalidRequestException if a problem occurs while add the input value */ public abstract void addInput(ProtocolVersion protocolVersion, ResultSetBuilder rs) throws InvalidRequestException; /** * Returns the selector output. * * @param protocolVersion protocol version used for serialization * @return the selector output * @throws InvalidRequestException if a problem occurs while computing the output value */ public abstract ByteBuffer getOutput(ProtocolVersion protocolVersion) throws InvalidRequestException; /** * Returns the Selector output type. * * @return the Selector output type. */ public abstract AbstractType getType(); /** * Checks if this Selector is creating aggregates. * * @return true if this Selector is creating aggregates false * otherwise. */ public boolean isAggregate() { return false; } /** * Reset the internal state of this Selector. */ public abstract void reset(); /** * Returns a string representation of the identifier that is safe to use directly in CQL queries. * If necessary, the string will be double-quoted, and any quotes inside the string will be escaped. */ public String toCQLString() { return toString(); } }




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