Package org.datanucleus.store.query.compiler

Class VarThisCompilationOptimiser

java.lang.Object

org.datanucleus.store.query.compiler.VarThisCompilationOptimiser

All Implemented Interfaces:

CompilationOptimiser

public class VarThisCompilationOptimiser
extends java.lang.Object
implements CompilationOptimiser

Optimiser for query compilation that searches for variable equality like "var == this". Since the variable is the same as the candidate it will replace all instances of the variable with the candidate. TODO We should only update "var == this" in the same branch of the filter (i.e not if used in other branches of the filter) Applies to the FILTER only.

Field Summary

Fields

Modifier and Type	Field	Description
(package private) QueryCompilation	compilation	The compilation that we are optimising.

Constructor Summary

Constructors

Constructor	Description
VarThisCompilationOptimiser(QueryCompilation compilation, MetaDataManager unused, ClassLoaderResolver clr)

Method Summary

Modifier and Type	Method	Description
private void	findRedundantFilterVariables(Expression filterExpr, java.util.Set<java.lang.String> varNames)	Method to process the provided filter expression and find any variables that are to all intents and purposes redundant.
void	optimise()	Method to perform the optimisation.
private Expression	replaceVariableWithCandidateInExpression(java.lang.String varName, Expression expr)	Method that replaces any occurrence of the specified variable in the provided expression with the candidate primary expression.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Field Detail

compilation

QueryCompilation compilation

The compilation that we are optimising.

Constructor Detail

VarThisCompilationOptimiser

public VarThisCompilationOptimiser(QueryCompilation compilation,
                                   MetaDataManager unused,
                                   ClassLoaderResolver clr)

Method Detail

optimise

public void optimise()

Description copied from interface: CompilationOptimiser

Method to perform the optimisation.

Specified by:

optimise in interface CompilationOptimiser

replaceVariableWithCandidateInExpression

private Expression replaceVariableWithCandidateInExpression(java.lang.String varName,
                                                            Expression expr)

Method that replaces any occurrence of the specified variable in the provided expression with the candidate primary expression. Recurses to sub-expressions.

Parameters:

varName - Variable name

expr - The expression to update

Returns:

Updated expression

findRedundantFilterVariables

private void findRedundantFilterVariables(Expression filterExpr,
                                          java.util.Set<java.lang.String> varNames)

Method to process the provided filter expression and find any variables that are to all intents and purposes redundant. Checks for "var == this". In this case we can just replace the variable occurrences with "this".

Parameters:

filterExpr - The filter

varNames - The variable names that are redundant (updated by this method)