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EagerAggregationPipe.scala
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/
EagerAggregationPipe.scala
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/**
* Copyright (c) 2002-2012 "Neo Technology,"
* Network Engine for Objects in Lund AB [http://neotechnology.com]
*
* This file is part of Neo4j.
*
* Neo4j is free software: you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation, either version 3 of the License, or
* (at your option) any later version.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program. If not, see <http://www.gnu.org/licenses/>.
*/
package org.neo4j.cypher.internal.pipes
import aggregation.AggregationFunction
import org.neo4j.cypher.internal.symbols._
import org.neo4j.cypher.internal.commands.expressions.{Expression, AggregationExpression}
import collection.mutable.{Map => MutableMap}
// Eager aggregation means that this pipe will eagerly load the whole resulting sub graphs before starting
// to emit aggregated results.
// Cypher is lazy until it can't - this pipe will eagerly load the full match
class EagerAggregationPipe(source: Pipe, val keyExpressions: Map[String, Expression], aggregations: Map[String, AggregationExpression])
extends PipeWithSource(source) {
def oldKeyExpressions = keyExpressions.values.toSeq
val symbols: SymbolTable = createSymbols2()
private def createSymbols2() = {
val typeExtractor: ((String, Expression)) => (String, CypherType) = {
case (id, exp) => id -> exp.getType(source.symbols)
}
val keyIdentifiers = keyExpressions.map(typeExtractor)
val aggrIdentifiers = aggregations.map(typeExtractor)
new SymbolTable(keyIdentifiers ++ aggrIdentifiers)
}
def createResults(state: QueryState): Traversable[ExecutionContext] = {
// This is the temporary storage used while the aggregation is going on
val result = MutableMap[NiceHasher, (ExecutionContext, Seq[AggregationFunction])]()
val keyNames: Seq[String] = keyExpressions.map(_._1).toSeq
val aggregationNames: Seq[String] = aggregations.map(_._1).toSeq
source.createResults(state).foreach(ctx => {
val groupValues: NiceHasher = new NiceHasher(keyNames.map(ctx(_)))
val (_, functions) = result.getOrElseUpdate(groupValues, (ctx, aggregations.map(_._2.createAggregationFunction).toSeq))
functions.foreach(func => func(ctx))
})
val resultContext = if (result.isEmpty && keyNames.isEmpty) {
createEmptyResult(aggregationNames)
} else result.map {
case (key, (ctx, aggregator)) => createResults(keyNames, key, aggregationNames, aggregator, ctx)
}
resultContext
}
def createResults(keyNames: scala.Seq[String], key: NiceHasher, aggregationNames: scala.Seq[String], aggregator: scala.Seq[AggregationFunction], ctx: ExecutionContext): ExecutionContext = {
val newMap = MutableMaps.create
//add key values
(keyNames zip key.original).foreach(newMap += _)
//add aggregated values
(aggregationNames zip aggregator.map(_.result)).foreach(newMap += _)
ctx.newFrom(newMap)
}
private def createEmptyResult(aggregationNames: Seq[String]): Traversable[ExecutionContext] = {
val newMap = MutableMaps.create
val aggregationNamesAndFunctions = aggregationNames zip aggregations.map(_._2.createAggregationFunction.result)
aggregationNamesAndFunctions.toMap
.foreach {
case (name, zeroValue) => newMap += name -> zeroValue
}
Traversable(ExecutionContext(newMap))
}
override def executionPlan(): String = source.executionPlan() + "\r\n" + "EagerAggregation( keys: [" + oldKeyExpressions.mkString(", ") + "], aggregates: [" + aggregations.mkString(", ") + "])"
def assertTypes(symbols: SymbolTable) {
keyExpressions.foreach(_._2.assertTypes(symbols))
aggregations.foreach(_._2.assertTypes(symbols))
}
}