org.exist.xquery
Class GeneralComparison

java.lang.Object
  org.exist.xquery.AbstractExpression
      org.exist.xquery.PathExpr
          org.exist.xquery.BinaryOp
              org.exist.xquery.GeneralComparison

All Implemented Interfaces:

CompiledXQuery, Expression, IndexUseReporter, Optimizable, RewritableExpression, org.xmldb.api.base.CompiledExpression

Direct Known Subclasses:

ValueComparison

public class GeneralComparison
extends BinaryOp
implements Optimizable, IndexUseReporter

A general XQuery/XPath2 comparison expression.

Nested Class Summary

static class

GeneralComparison.IndexFlags

Field Summary

protected CachedResult	cached The class might cache the entire results of a previous execution.
protected java.lang.Object	collationArg Extra argument (to standard functions starts-with/contains etc.) to indicate the collation to be used for string comparisons.
protected boolean	invalidNodeEvaluation
protected boolean	inWhereClause Set to true if this expression is called within the where clause of a FLWOR expression.
protected boolean	optimizeChild
protected boolean	optimizeSelf
protected int	relation The type of operator used for the comparison, i.e.
protected int	rightOpDeps
protected int	truncation Truncation flags: when comparing with a string value, the search string may be truncated with a single * wildcard.

Fields inherited from class org.exist.xquery.PathExpr

inPredicate, keepVirtual, LOG, parent, staticContext, steps

Fields inherited from class org.exist.xquery.AbstractExpression

column, context, contextDocSet, contextId, line, unordered

Fields inherited from interface org.exist.xquery.Expression

DOT_TEST, EXPRESSION_ID_INVALID, IGNORE_CONTEXT, IN_NODE_CONSTRUCTOR, IN_PREDICATE, IN_UPDATE, IN_WHERE_CLAUSE, NEED_INDEX_INFO, NO_CONTEXT_ID, NON_STREAMABLE, POSITIONAL_PREDICATE, SINGLE_STEP_EXECUTION, UNORDERED, USE_TREE_TRAVERSAL

Constructor Summary

GeneralComparison(XQueryContext context, Expression left, Expression right, int relation)

GeneralComparison(XQueryContext context, Expression left, Expression right, int relation, int truncation)

GeneralComparison(XQueryContext context, int relation)

GeneralComparison(XQueryContext context, int relation, int truncation)

Method Summary

void	accept(ExpressionVisitor visitor) Start traversing the expression tree using the specified ExpressionVisitor.
void	analyze(AnalyzeContextInfo contextInfo) Statically analyze the expression and its subexpressions.
boolean	canOptimize(Sequence contextSequence)
static GeneralComparison.IndexFlags	checkForQNameIndex(GeneralComparison.IndexFlags idxflags, XQueryContext context, Sequence contextSequence, QName contextQName)
void	dump(ExpressionDumper dumper) Write a diagnostic dump of the expression to the passed ExpressionDumper.
Sequence	eval(Sequence contextSequence, Item contextItem) Evaluate the expression represented by this object.
protected Sequence	genericCompare(Sequence contextSequence, Item contextItem) Generic, slow implementation.
protected Sequence	genericCompare(Sequence ls, Sequence contextSequence, Item contextItem)
protected java.text.Collator	getCollator(Sequence contextSequence)
int	getDependencies() Returns Dependency.DEFAULT_DEPENDENCIES.
int	getOptimizeAxis()
int	getRelation()
boolean	hasUsedIndex()
protected Sequence	nodeSetCompare(NodeSet nodes, Sequence contextSequence) Optimized implementation, which can be applied if the left operand returns a node set.
boolean	optimizeOnChild()
boolean	optimizeOnSelf()
NodeSet	preSelect(Sequence contextSequence, boolean useContext)
protected Sequence	quickNodeSetCompare(Sequence contextSequence) Optimized implementation: first checks if a range index is defined on the nodes in the left argument.
void	resetState(boolean postOptimization) Called to inform an expression that it should reset to its initial state.
int	returnsType() The static return type of the expression.
void	setCollation(java.lang.Object collationArg)
protected void	simplifyOperands() Possibly switch operands to simplify execution.
protected void	switchOperands()
java.lang.String	toString()

Methods inherited from class org.exist.xquery.BinaryOp

getLeft, getRight, setContextDocSet, setLeft, setRight, simplify

Methods inherited from class org.exist.xquery.PathExpr

add, add, addPath, addPredicate, allowMixNodesInReturn, dump, getCardinality, getColumn, getContext, getDocumentSet, getExpression, getLastExpression, getLength, getLine, getLiteralValue, getParent, getPrimaryAxis, getSubExpression, getSubExpressionCount, isValid, replaceExpression, replaceLastExpression, reset, setContext, setPrimaryAxis, setUseStaticContext

Methods inherited from class org.exist.xquery.AbstractExpression

eval, getContextDocSet, getContextId, getExpressionId, getSource, match, needsReset, setASTNode, setContextId, setLocation

Methods inherited from class java.lang.Object

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

Methods inherited from interface org.exist.xquery.Expression

allowMixNodesInReturn, eval, getCardinality, getColumn, getContext, getContextDocSet, getContextId, getExpressionId, getLine, getParent, getPrimaryAxis, getSource, getSubExpression, getSubExpressionCount, match, needsReset, setASTNode, setContextDocSet, setContextId, setLocation, setPrimaryAxis, simplify

Methods inherited from interface org.exist.xquery.CompiledXQuery

eval, getSource

Field Detail

relation

protected int relation

The type of operator used for the comparison, i.e. =, !=, <, > ... One of the constants declared in class Constants.

truncation

protected int truncation

Truncation flags: when comparing with a string value, the search string may be truncated with a single * wildcard. See the constants declared in class Constants.

The standard functions starts-with, ends-with and contains are transformed into a general comparison with wildcard. Hence the need to consider wildcards here.

cached

protected CachedResult cached

The class might cache the entire results of a previous execution.

collationArg

protected java.lang.Object collationArg

Extra argument (to standard functions starts-with/contains etc.) to indicate the collation to be used for string comparisons.

inWhereClause

protected boolean inWhereClause

Set to true if this expression is called within the where clause of a FLWOR expression.

invalidNodeEvaluation

protected boolean invalidNodeEvaluation

rightOpDeps

protected int rightOpDeps

optimizeSelf

protected boolean optimizeSelf

optimizeChild

protected boolean optimizeChild

Constructor Detail

GeneralComparison

public GeneralComparison(XQueryContext context,
                         int relation)

GeneralComparison

public GeneralComparison(XQueryContext context,
                         int relation,
                         int truncation)

GeneralComparison

public GeneralComparison(XQueryContext context,
                         Expression left,
                         Expression right,
                         int relation)

GeneralComparison

public GeneralComparison(XQueryContext context,
                         Expression left,
                         Expression right,
                         int relation,
                         int truncation)

Method Detail

analyze

public void analyze(AnalyzeContextInfo contextInfo)
             throws XPathException

Description copied from interface: Expression

Statically analyze the expression and its subexpressions. During the static analysis phase, the query engine can detect unknown variables and some type errors.

Specified by:

analyze in interface Expression

Overrides:

analyze in class BinaryOp

Throws:

XPathException

canOptimize

public boolean canOptimize(Sequence contextSequence)

Specified by:

canOptimize in interface Optimizable

optimizeOnSelf

public boolean optimizeOnSelf()

Specified by:

optimizeOnSelf in interface Optimizable

optimizeOnChild

public boolean optimizeOnChild()

Specified by:

optimizeOnChild in interface Optimizable

getOptimizeAxis

public int getOptimizeAxis()

Specified by:

getOptimizeAxis in interface Optimizable

returnsType

public int returnsType()

Description copied from interface: Expression

The static return type of the expression. This method should return one of the type constants defined in class Type. If the return type cannot be determined statically, return Type.ITEM.

Specified by:

returnsType in interface Expression

Overrides:

returnsType in class BinaryOp

getDependencies

public int getDependencies()

Description copied from class: AbstractExpression

Returns Dependency.DEFAULT_DEPENDENCIES.

Specified by:

getDependencies in interface Expression

Overrides:

getDependencies in class PathExpr

Returns:

set of bit-flags

See Also:

Expression.getDependencies()

getRelation

public int getRelation()

preSelect

public NodeSet preSelect(Sequence contextSequence,
                         boolean useContext)
                  throws XPathException

Specified by:

preSelect in interface Optimizable

Throws:

XPathException

eval

public Sequence eval(Sequence contextSequence,
                     Item contextItem)
              throws XPathException

Description copied from interface: Expression

Evaluate the expression represented by this object. Depending on the context in which this expression is executed, either the context sequence, the context item or both of them may be set. An implementing class should know how to handle this. The general contract is as follows: if the Dependency.CONTEXT_ITEM bit is set in the bit field returned by Expression.getDependencies(), the eval method will be called once for every item in the context sequence. The contextItem parameter will be set to the current item. Otherwise, the eval method will only be called once for the whole context sequence and contextItem will be null. eXist tries to process the entire context set in one, single step whenever possible. Thus, most classes only expect context to contain a list of nodes which represents the current context of the expression. The position() function in XPath is an example for an expression, which requires both, context sequence and context item to be set. The context sequence might be a node set, a sequence of atomic values or a single node or atomic value.

Specified by:

eval in interface Expression

Specified by:

eval in class BinaryOp

Parameters:

contextSequence - the current context sequence.

contextItem - a single item, taken from context. This defines the item, the expression should work on.

Throws:

XPathException

genericCompare

protected Sequence genericCompare(Sequence contextSequence,
                                  Item contextItem)
                           throws XPathException

Generic, slow implementation. Applied if none of the possible optimizations can be used.

Parameters:

contextSequence -

contextItem -

Returns:

The Sequence resulting from the comparison

Throws:

XPathException

genericCompare

protected Sequence genericCompare(Sequence ls,
                                  Sequence contextSequence,
                                  Item contextItem)
                           throws XPathException

Throws:

XPathException

nodeSetCompare

protected Sequence nodeSetCompare(NodeSet nodes,
                                  Sequence contextSequence)
                           throws XPathException

Optimized implementation, which can be applied if the left operand returns a node set. In this case, the left expression is executed first. All matching context nodes are then passed to the right expression.

Parameters:

nodes - DOCUMENT ME!

contextSequence - DOCUMENT ME!

Returns:

DOCUMENT ME!

Throws:

XPathException - DOCUMENT ME!

quickNodeSetCompare

protected Sequence quickNodeSetCompare(Sequence contextSequence)
                                throws XPathException

Optimized implementation: first checks if a range index is defined on the nodes in the left argument. If that fails, check if we can use the fulltext index to speed up the search. Otherwise, fall back to nodeSetCompare(NodeSet, Sequence).

Parameters:

contextSequence - DOCUMENT ME!

Returns:

DOCUMENT ME!

Throws:

XPathException - DOCUMENT ME!

hasUsedIndex

public boolean hasUsedIndex()

Specified by:

hasUsedIndex in interface IndexUseReporter

dump

public void dump(ExpressionDumper dumper)

Description copied from interface: Expression

Write a diagnostic dump of the expression to the passed ExpressionDumper.

Specified by:

dump in interface Expression

Overrides:

dump in class PathExpr

Parameters:

dumper - the expression dumper to write to

toString

public java.lang.String toString()

Overrides:

toString in class PathExpr

switchOperands

protected void switchOperands()

simplifyOperands

protected void simplifyOperands()

Possibly switch operands to simplify execution.

getCollator

protected java.text.Collator getCollator(Sequence contextSequence)
                                  throws XPathException

Throws:

XPathException

setCollation

public void setCollation(java.lang.Object collationArg)

checkForQNameIndex

public static final GeneralComparison.IndexFlags checkForQNameIndex(GeneralComparison.IndexFlags idxflags,
                                                                    XQueryContext context,
                                                                    Sequence contextSequence,
                                                                    QName contextQName)

resetState

public void resetState(boolean postOptimization)

Description copied from interface: Expression

Called to inform an expression that it should reset to its initial state. All cached data in the expression object should be dropped. For example, the xmldb:document() function calls this method whenever the input document set has changed.

Specified by:

resetState in interface Expression

Overrides:

resetState in class PathExpr

accept

public void accept(ExpressionVisitor visitor)

Description copied from interface: Expression

Start traversing the expression tree using the specified ExpressionVisitor.

Specified by:

accept in interface Expression

Overrides:

accept in class PathExpr