com.saxonica.ee.stream

Class CurrentGroupPattern

java.lang.Object

net.sf.saxon.expr.Expression

net.sf.saxon.expr.PseudoExpression

net.sf.saxon.pattern.Pattern

net.sf.saxon.pattern.AnchorPattern

com.saxonica.ee.stream.CurrentGroupPattern

All Implemented Interfaces:

ExportAgent, Locatable, IdentityComparable

public class CurrentGroupPattern
extends AnchorPattern

This is a special pattern that matches the "anchor node". It is used for the selectors that arise when evaluating XPath expressions in streaming mode; the anchor node is the context node for the streamed XPath evaluation. Given a streamed evaluation of an expression such as ./BOOKS/BOOK/PRICE, the way we evaluate this is to turn it into a pattern, which is then tested against all descendant nodes. Conceptually the pattern is $A/BOOKS/BOOK/PRICE, where $A is referred to as the anchor node. When we evaluate the pattern against (say) a PRICE element, the match will only succeed if the name of the element is "PRICE" and its ancestors are, in order, a BOOK element, a BOOKS element, and the anchor node $A.

Field Summary

Fields inherited from class net.sf.saxon.expr.Expression

EFFECTIVE_BOOLEAN_VALUE, EVALUATE_METHOD, ITEM_FEED_METHOD, ITERATE_METHOD, MAX_COST, MAX_SEQUENCE_LENGTH, MAX_STRING_LENGTH, PROCESS_METHOD, staticProperties, UNBOUNDED_LOWER, UNBOUNDED_UPPER, UPDATE_METHOD, WATCH_METHOD

Constructor Summary

Constructors

Modifier	Constructor and Description
protected	CurrentGroupPattern()

Method Summary

Modifier and Type	Method and Description
void	export(ExpressionPresenter presenter) Diagnostic print of expression structure.
static CurrentGroupPattern	getInstance()
boolean	matchesBeneathAnchor(NodeInfo node, NodeInfo anchor, XPathContext context) Determine whether this pattern matches a given Node within the subtree rooted at a given anchor node.
boolean	matchesCurrentGroup() Ask whether the pattern is anchored on a call on current-group()

Methods inherited from class net.sf.saxon.pattern.AnchorPattern

copy, getItemType, getUType, matches, toString, typeCheck

Methods inherited from class net.sf.saxon.pattern.Pattern

allocateSlots, bindCurrent, convertToTypedPattern, effectiveBooleanValue, getDefaultPriority, getDependencies, getFingerprint, getHostLanguage, handleDynamicError, isLiftable, isMotionless, isRecoverable, make, optimize, patternContainsVariable, replaceCurrent, selectNodes, setOriginalText, setPriority, setRecoverable, simplify, toShortString

Methods inherited from class net.sf.saxon.expr.PseudoExpression

computeCardinality, evaluateAsString, evaluateItem, getImplementationMethod, iterate, process

Methods inherited from class net.sf.saxon.expr.Expression

addToPathMap, adoptChildExpression, allowExtractingCommonSubexpressions, checkedOperands, checkForUpdatingSubexpressions, checkPermittedContents, computeDependencies, computeHashCode, computeSpecialProperties, computeStaticProperties, dynamicError, equals, evaluatePendingUpdates, explain, getCardinality, getConfiguration, getConstructType, getCost, getEvaluationMethod, getExpressionName, getExtraProperty, getIntegerBounds, getInterpretedExpression, getIntrinsicDependencies, getLocalRetainedStaticContext, getLocation, getNetCost, getObjectName, getPackageData, getParentExpression, getProperties, getProperty, getRetainedStaticContext, getScopingExpression, getSlotsUsed, getSpecialProperties, getStaticBaseURI, getStaticBaseURIString, getStaticType, getStaticUType, getStreamerName, hasCompatibleStaticContext, hashCode, hasSpecialProperty, hasVariableBinding, identityHashCode, implementsStaticTypeCheck, isCallOn, isEqual, isIdentical, isInstruction, isMultiThreaded, isStaticPropertiesKnown, isSubtreeExpression, isUpdatingExpression, isVacuousExpression, markTailFunctionCalls, operandList, operands, operandSparseList, optimizeChildren, prepareForStreaming, resetLocalStaticProperties, restoreParentPointers, setEvaluationMethod, setExtraProperty, setFiltered, setFlattened, setLocation, setParentExpression, setRetainedStaticContext, setRetainedStaticContextLocally, setRetainedStaticContextThoroughly, setStaticProperty, simplifyChildren, staticTypeCheck, suppressValidation, toPattern, typeCheckChildren, typeError, unordered, verifyParentPointers

Methods inherited from class java.lang.Object

clone, finalize, getClass, notify, notifyAll, wait, wait, wait

Constructor Detail

CurrentGroupPattern

protected CurrentGroupPattern()

Method Detail

getInstance

public static CurrentGroupPattern getInstance()

matchesCurrentGroup

public boolean matchesCurrentGroup()

Ask whether the pattern is anchored on a call on current-group()

Overrides:

matchesCurrentGroup in class Pattern

Returns:

true if calls on matchesBeneathAnchor should test with all nodes in the current group as anchor nodes. If false, only the first node in a group is treated as the anchor node

matchesBeneathAnchor

public boolean matchesBeneathAnchor(NodeInfo node,
                                    NodeInfo anchor,
                                    XPathContext context)
                             throws XPathException

Description copied from class: AnchorPattern

Determine whether this pattern matches a given Node within the subtree rooted at a given anchor node. This method is used when the pattern is used for streaming.

Overrides:

matchesBeneathAnchor in class AnchorPattern

Parameters:

node - The NodeInfo representing the Element or other node to be tested against the Pattern

anchor - The anchor node, which must match any AnchorPattern subpattern

context - The dynamic context. Only relevant if the pattern uses variables, or contains calls on functions such as document() or key().

Returns:

true if the node matches the Pattern, false otherwise

Throws:

XPathException - if an error occurs while matching the pattern (the caller will usually treat this the same as a false result)

export

public void export(ExpressionPresenter presenter)
            throws XPathException

Description copied from class: Expression

Diagnostic print of expression structure. The abstract expression tree is written to the supplied output destination.

Specified by:

export in interface ExportAgent

Overrides:

export in class AnchorPattern

Parameters:

presenter - the expression presenter used to display the structure

Throws:

XPathException - if the export fails, for example if an expression is found that won't work in the target environment.