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[refactor] Refactor the predicate position() optimisation into a Quer…
…yRewriter
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exist-core/src/main/java/org/exist/xquery/PositionalPredicateRewriter.java
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| Original file line number | Diff line number | Diff line change |
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| @@ -0,0 +1,85 @@ | ||
| /* | ||
| * Copyright (c) 2014, Evolved Binary Ltd | ||
| */ | ||
| package org.exist.xquery; | ||
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| import com.evolvedbinary.j8fu.tuple.Tuple2; | ||
| import org.exist.xquery.functions.fn.FunPosition; | ||
| import org.exist.xquery.value.Type; | ||
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| import javax.annotation.Nullable; | ||
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| import static com.evolvedbinary.j8fu.tuple.Tuple.Tuple; | ||
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| /** | ||
| * Rewrite position() withing a predicate to a POSITIONAL version of the predicate where possible. | ||
| * | ||
| * @author <a href="mailto:[email protected]">Adam Retter</a> | ||
| */ | ||
| public class PositionalPredicateRewriter extends QueryRewriter { | ||
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| public PositionalPredicateRewriter(final XQueryContext context) { | ||
| super(context); | ||
| } | ||
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| @Override | ||
| public Pragma rewriteLocationStep(final LocationStep locationStep) throws XPathException { | ||
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| @Nullable final Predicate[] predicates = locationStep.getPredicates(); | ||
| if (predicates != null) { | ||
| for (final Predicate predicate : predicates) { | ||
| @Nullable final Tuple2<Expression, LiteralValue> predicateOptimizableInnerExpr = canOptimizeToPositionalPredicate(predicate); | ||
| if (predicateOptimizableInnerExpr != null) { | ||
| predicate.replace(predicateOptimizableInnerExpr._1, predicateOptimizableInnerExpr._2); | ||
| } | ||
| } | ||
| } | ||
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| return null; | ||
| } | ||
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| /** | ||
| * Test whether we can optimise position() withing a predicate to a POSITIONAL version of a predicate. | ||
| * | ||
| * @param predicate the predicate to test | ||
| * | ||
| * @return the inner expr to be replaced and the literal value to replace it with if it can be optimised, null otherwise. | ||
| */ | ||
| private @Nullable Tuple2<Expression, LiteralValue> canOptimizeToPositionalPredicate(final Predicate predicate) { | ||
| if (predicate.getSubExpressionCount() == 1) { | ||
| final org.exist.xquery.Expression predInnerExpr = predicate.getSubExpression(0); | ||
| if (predInnerExpr instanceof ValueComparison) { | ||
| final ValueComparison valueComparison = (ValueComparison) predInnerExpr; | ||
| if (valueComparison.getRelation() == Constants.Comparison.EQ) { | ||
| final org.exist.xquery.Expression left = valueComparison.getLeft(); | ||
| final org.exist.xquery.Expression right = valueComparison.getRight(); | ||
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| if (left instanceof InternalFunctionCall | ||
| && right instanceof org.exist.xquery.LiteralValue) { | ||
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| final InternalFunctionCall leftInternalFunctionCall = (InternalFunctionCall) left; | ||
| final org.exist.xquery.LiteralValue rightLiteralValue = (org.exist.xquery.LiteralValue) right; | ||
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| if (leftInternalFunctionCall.getFunction() instanceof FunPosition && rightLiteralValue.returnsType() == Type.INTEGER) { | ||
| // NOTE(AR) if the predicate is like [position() eq 1] or [position() = 1] then we could rewrite it to [1] | ||
| return Tuple(predInnerExpr, rightLiteralValue); | ||
| } | ||
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| } else if (left instanceof org.exist.xquery.LiteralValue | ||
| && right instanceof InternalFunctionCall) { | ||
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| final org.exist.xquery.LiteralValue leftLiteralValue = (org.exist.xquery.LiteralValue) left; | ||
| final InternalFunctionCall rightInternalFunctionCall = (InternalFunctionCall) right; | ||
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| if (leftLiteralValue.returnsType() == Type.INTEGER | ||
| && rightInternalFunctionCall.getFunction() instanceof FunPosition) { | ||
| // NOTE(AR) if the predicate is like [1 eq position()] or [1 = position()] then we could rewrite it to [1] | ||
| return Tuple(predInnerExpr, leftLiteralValue); | ||
| } | ||
| } | ||
| } | ||
| } | ||
| } | ||
| return null; | ||
| } | ||
| } |