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groupInequalityPredicates.scala
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groupInequalityPredicates.scala
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/*
* Copyright (c) 2002-2017 "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.compiler.v3_3.ast.convert.plannerQuery
import org.neo4j.cypher.internal.frontend.v3_4.ast.{AndedPropertyInequalities, InequalityExpression, Property, Variable}
import org.neo4j.cypher.internal.frontend.v3_4.helpers.NonEmptyList
import org.neo4j.cypher.internal.frontend.v3_4.helpers.NonEmptyList._
import org.neo4j.cypher.internal.ir.v3_3.Predicate
// This transforms
//
// Seq(Pred[n](n.prop > 34), Pred[n](n.foo = 'bar'), Pred[n](n.prop >= n.goo))
//
// into
//
// Seq(Pred[n](n.foo = 'bar'), Pred[n](AndedInequalities(n, n.prop, Seq(n.prop > 34, n.prop >= n.goo))
//
// i.e it groups inequalities by property lookup and collects each group of inequalities into
// an instance of AndedPropertyInequalities
//
object groupInequalityPredicates extends (NonEmptyList[Predicate] => NonEmptyList[Predicate]) {
def apply(inputPredicates: NonEmptyList[Predicate]): NonEmptyList[Predicate] = {
// categorize predicates according to whether they contain an inequality or not
val partitions = inputPredicates.partition { (predicate: Predicate) =>
predicate.expr match {
case inequality: InequalityExpression => Left(predicate -> inequality)
case _ => Right(predicate)
}
}
// detect if we need to transform the input
val optInequalities = partitions match {
case Left(parts) => Some(parts)
case Right((Some(inequalities), remainder)) => Some(inequalities -> Some(remainder))
case Right((None, _)) => None
}
optInequalities match {
case Some((inequalities, optRemainder)) =>
// group by property lookup
val groupedPredicates = groupedInequalities(inequalities)
// collect together all inequalities over some property lookup
val combinedInequalityPredicates = groupedPredicates.map {
case (Some((ident, prop)), groupInequalities) =>
val deps = groupInequalities.map { case (predicate, _) => predicate.dependencies }.toSet.flatten
val expr = AndedPropertyInequalities(ident, prop, groupInequalities.map { case (_, inequality) => inequality })
NonEmptyList(Predicate(deps, expr))
case (None, predicates) =>
predicates.map { case (predicate, _) => predicate }
}.flatMap[Predicate](identity)
// concatenate with remaining predicates
optRemainder.map(_ ++ combinedInequalityPredicates).getOrElse(combinedInequalityPredicates)
case None =>
inputPredicates
}
}
private def groupedInequalities(inequalities: NonEmptyList[(Predicate, InequalityExpression)]) = {
inequalities.groupBy { (input: (Predicate, InequalityExpression)) =>
val (_, inequality) = input
inequality.lhs match {
case prop@Property(ident: Variable, _) => Some(ident -> prop)
case _ => None
}
}.toNonEmptyListOption.get
}
}