net.sf.saxon.instruct

Class ForEachGroup

Implemented Interfaces:
ContextMappingFunction, EvaluableItem, InstructionInfoProvider, SequenceIterable, Serializable, SortKeyEvaluator, SourceLocator, TailCallReturner

public class ForEachGroup
extends Instruction
implements ContextMappingFunction, SortKeyEvaluator

Handler for xsl:for-each-group elements in stylesheet. This is a new instruction defined in XSLT 2.0

Field Summary

static int
GROUP_ADJACENT
static int
GROUP_BY
static int
GROUP_ENDING
static int
GROUP_STARTING

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

EVALUATE_METHOD, ITERATE_METHOD, PROCESS_METHOD, locationId, staticProperties

Constructor Summary

ForEachGroup(Expression select, Expression action, byte algorithm, Expression key, StringCollator collator, Expression collationNameExpression, String baseURI, SortKeyDefinition[] sortKeys)
Create a for-each-group instruction

Method Summary

PathMap.PathMapNodeSet
addToPathMap(PathMap pathMap, PathMap.PathMapNodeSet pathMapNodeSet)
Add a representation of this expression to a PathMap.
void
checkPermittedContents(SchemaType parentType, StaticContext env, boolean whole)
Check that any elements and attributes constructed or returned by this expression are acceptable in the content model of a given complex type.
int
computeDependencies()
Compute the dependencies of an expression, as the union of the dependencies of its subexpressions.
Expression
copy()
Copy an expression.
boolean
createsNewNodes()
Determine whether this instruction creates new nodes.
Item
evaluateSortKey(int n, XPathContext c)
Callback for evaluating the sort keys
void
explain(ExpressionPresenter out)
Diagnostic print of expression structure.
Expression
getActionExpression()
Get the action expression (the content of the for-each-group)
Expression
getGroupingKey()
Get the grouping key expression expression (the group-by or group-adjacent expression, or a PatternSponsor containing the group-starting-with or group-ending-with expression)
int
getInstructionNameCode()
Get the name of this instruction for diagnostic and tracing purposes
ItemType
getItemType(TypeHierarchy th)
Get the item type of the items returned by evaluating this instruction
boolean
hasLoopingSubexpression(Expression child)
Given an expression that is an immediate child of this expression, test whether the evaluation of the parent expression causes the child expression to be evaluated repeatedly
SequenceIterator
iterate(XPathContext context)
Return an Iterator to iterate over the values of a sequence.
Iterator
iterateSubExpressions()
Get all the XPath expressions associated with this instruction (in XSLT terms, the expression present on attributes of the instruction, as distinct from the child instructions in a sequence construction)
SequenceIterator
map(XPathContext context)
Map one item to a sequence.
Expression
optimize(ExpressionVisitor visitor, ItemType contextItemType)
Perform optimisation of an expression and its subexpressions.
TailCall
processLeavingTail(XPathContext context)
ProcessLeavingTail: called to do the real work of this instruction.
protected void
promoteInst(PromotionOffer offer)
Handle promotion offers, that is, non-local tree rewrites.
boolean
replaceSubExpression(Expression original, Expression replacement)
Replace one subexpression by a replacement subexpression
Expression
simplify(ExpressionVisitor visitor)
Simplify an expression.
Expression
typeCheck(ExpressionVisitor visitor, ItemType contextItemType)
Perform type checking of an expression and its subexpressions.

Methods inherited from class net.sf.saxon.instruct.Instruction

assembleParams, assembleTunnelParams, computeCardinality, computeSpecialProperties, createsNewNodes, dynamicError, evaluateAsString, evaluateItem, getImplementationMethod, getInstructionInfo, getInstructionNameCode, getItemType, getSourceLocator, isXSLT, iterate, process, processLeavingTail, promote, promoteInst, simplify

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

addToPathMap, adoptChildExpression, checkPermittedContents, computeCardinality, computeDependencies, computeSpecialProperties, computeStaticProperties, copy, display, doPromotion, dynamicError, effectiveBooleanValue, evaluateAsString, evaluateItem, explain, explain, findParentOf, getCardinality, getColumnNumber, getConstructType, getContainer, getDependencies, getExecutable, getHostLanguage, getImplementationMethod, getInstructionInfo, getIntrinsicDependencies, getItemType, getLineNumber, getLocationId, getLocationProvider, getPublicId, getSlotsUsed, getSpecialProperties, getSystemId, hasLoopingSubexpression, implementsStaticTypeCheck, iterate, iterateEvents, iterateSubExpressions, markTailFunctionCalls, optimize, process, promote, replaceSubExpression, resetLocalStaticProperties, setContainer, setFiltered, setFlattened, setLocationId, simplify, staticTypeCheck, suppressValidation, toString, typeCheck, typeError

Field Details

GROUP_ADJACENT

public static final int GROUP_ADJACENT
Field Value:
1

GROUP_BY

public static final int GROUP_BY
Field Value:
0

GROUP_ENDING

public static final int GROUP_ENDING
Field Value:
3

GROUP_STARTING

public static final int GROUP_STARTING
Field Value:
2

Constructor Details

ForEachGroup

public ForEachGroup(Expression select,
                    Expression action,
                    byte algorithm,
                    Expression key,
                    StringCollator collator,
                    Expression collationNameExpression,
                    String baseURI,
                    SortKeyDefinition[] sortKeys)
Create a for-each-group instruction
Parameters:
select - the select expression (selects the population to be grouped)
action - the body of the for-each-group (applied to each group in turn)
algorithm - one of group-by, group-adjacent, group-starting-with, group-ending-with
key - expression to evaluate the grouping key
collator - user for comparing strings
collationNameExpression - expression that yields the name of the collation to be used
baseURI - static base URI of the expression
sortKeys - list of xsl:sort keys for sorting the groups

Method Details

addToPathMap

public PathMap.PathMapNodeSet addToPathMap(PathMap pathMap,
                                           PathMap.PathMapNodeSet pathMapNodeSet)
Add a representation of this expression to a PathMap. The PathMap captures a map of the nodes visited by an expression in a source tree.

The default implementation of this method assumes that an expression does no navigation other than the navigation done by evaluating its subexpressions, and that the subexpressions are evaluated in the same context as the containing expression. The method must be overridden for any expression where these assumptions do not hold. For example, implementations exist for AxisExpression, ParentExpression, and RootExpression (because they perform navigation), and for the doc(), document(), and collection() functions because they create a new navigation root. Implementations also exist for PathExpression and FilterExpression because they have subexpressions that are evaluated in a different context from the calling expression.

Overrides:
addToPathMap in interface Expression
Parameters:
pathMap - the PathMap to which the expression should be added
pathMapNodeSet -
Returns:
the pathMapNode representing the focus established by this expression, in the case where this expression is the first operand of a path expression or filter expression. For an expression that does navigation, it represents the end of the arc in the path map that describes the navigation route. For other expressions, it is the same as the input pathMapNode.

checkPermittedContents

public void checkPermittedContents(SchemaType parentType,
                                   StaticContext env,
                                   boolean whole)
            throws XPathException
Check that any elements and attributes constructed or returned by this expression are acceptable in the content model of a given complex type. It's always OK to say yes, since the check will be repeated at run-time. The process of checking element and attribute constructors against the content model of a complex type also registers the type of content expected of those constructors, so the static validation can continue recursively.
Overrides:
checkPermittedContents in interface Expression

computeDependencies

public int computeDependencies()
Compute the dependencies of an expression, as the union of the dependencies of its subexpressions. (This is overridden for path expressions and filter expressions, where the dependencies of a subexpression are not all propogated). This method should be called only once, to compute the dependencies; after that, getDependencies should be used.
Overrides:
computeDependencies in interface Expression
Returns:
the depencies, as a bit-mask

copy

public Expression copy()
Copy an expression. This makes a deep copy.
Overrides:
copy in interface Expression
Returns:
the copy of the original expression

createsNewNodes

public final boolean createsNewNodes()
Determine whether this instruction creates new nodes. This implementation returns true if the "action" creates new nodes. (Nodes created by the condition can't contribute to the result).
Overrides:
createsNewNodes in interface Instruction

evaluateSortKey

public Item evaluateSortKey(int n,
                            XPathContext c)
            throws XPathException
Callback for evaluating the sort keys
Specified by:
evaluateSortKey in interface SortKeyEvaluator

explain

public void explain(ExpressionPresenter out)
Diagnostic print of expression structure. The abstract expression tree is written to the supplied output destination.
Overrides:
explain in interface Expression

getActionExpression

public Expression getActionExpression()
Get the action expression (the content of the for-each-group)
Returns:
the body of the xsl:for-each-group instruction

getGroupingKey

public Expression getGroupingKey()
Get the grouping key expression expression (the group-by or group-adjacent expression, or a PatternSponsor containing the group-starting-with or group-ending-with expression)
Returns:
the expression used to calculate grouping keys

getInstructionNameCode

public int getInstructionNameCode()
Get the name of this instruction for diagnostic and tracing purposes
Overrides:
getInstructionNameCode in interface Instruction
Returns:
the name of the instruction

getItemType

public ItemType getItemType(TypeHierarchy th)
Get the item type of the items returned by evaluating this instruction
Overrides:
getItemType in interface Instruction
Parameters:
th - the type hierarchy cache
Returns:
the static item type of the instruction

hasLoopingSubexpression

public boolean hasLoopingSubexpression(Expression child)
Given an expression that is an immediate child of this expression, test whether the evaluation of the parent expression causes the child expression to be evaluated repeatedly
Overrides:
hasLoopingSubexpression in interface Expression
Parameters:
child - the immediate subexpression
Returns:
true if the child expression is evaluated repeatedly

iterate

public SequenceIterator iterate(XPathContext context)
            throws XPathException
Return an Iterator to iterate over the values of a sequence. The value of every expression can be regarded as a sequence, so this method is supported for all expressions. This default implementation relies on the process() method: it "pushes" the results of the instruction to a sequence in memory, and then iterates over this in-memory sequence.

In principle instructions should implement a pipelined iterate() method that avoids the overhead of intermediate storage.

Specified by:
iterate in interface SequenceIterable
Overrides:
iterate in interface Instruction
Parameters:
context - supplies the context for evaluation
Returns:
a SequenceIterator that can be used to iterate over the result of the expression
Throws:
XPathException - if any dynamic error occurs evaluating the expression

iterateSubExpressions

public Iterator iterateSubExpressions()
Get all the XPath expressions associated with this instruction (in XSLT terms, the expression present on attributes of the instruction, as distinct from the child instructions in a sequence construction)
Overrides:
iterateSubExpressions in interface Expression

map

public SequenceIterator map(XPathContext context)
            throws XPathException
Map one item to a sequence.
Specified by:
map in interface ContextMappingFunction
Parameters:
context - The processing context. This is supplied only for mapping constructs that set the context node, position, and size. Otherwise it is null.
Returns:
either (a) a SequenceIterator over the sequence of items that the supplied input item maps to, or (b) an Item if it maps to a single item, or (c) null if it maps to an empty sequence.

optimize

public Expression optimize(ExpressionVisitor visitor,
                           ItemType contextItemType)
            throws XPathException
Perform optimisation of an expression and its subexpressions. This is the third and final phase of static optimization.

This method is called after all references to functions and variables have been resolved to the declaration of the function or variable, and after all type checking has been done.

Overrides:
optimize in interface Expression
Parameters:
visitor - an expression visitor
contextItemType - the static type of "." at the point where this expression is invoked. The parameter is set to null if it is known statically that the context item will be undefined. If the type of the context item is not known statically, the argument is set to Type.ITEM_TYPE
Returns:
the original expression, rewritten if appropriate to optimize execution
Throws:
XPathException - if an error is discovered during this phase (typically a type error)

processLeavingTail

public TailCall processLeavingTail(XPathContext context)
            throws XPathException
ProcessLeavingTail: called to do the real work of this instruction. This method must be implemented in each subclass. The results of the instruction are written to the current Receiver, which can be obtained via the Controller.
Specified by:
processLeavingTail in interface TailCallReturner
Overrides:
processLeavingTail in interface Instruction
Parameters:
context - The dynamic context of the transformation, giving access to the current node, the current variables, etc.
Returns:
null if the instruction has completed execution; or a TailCall indicating a function call or template call that is delegated to the caller, to be made after the stack has been unwound so as to save stack space.

promoteInst

protected void promoteInst(PromotionOffer offer)
            throws XPathException
Handle promotion offers, that is, non-local tree rewrites.
Overrides:
promoteInst in interface Instruction
Parameters:
offer - The type of rewrite being offered
Throws:
XPathException -

replaceSubExpression

public boolean replaceSubExpression(Expression original,
                                    Expression replacement)
Replace one subexpression by a replacement subexpression
Overrides:
replaceSubExpression in interface Expression
Parameters:
original - the original subexpression
replacement - the replacement subexpression
Returns:
true if the original subexpression is found

simplify

public Expression simplify(ExpressionVisitor visitor)
            throws XPathException
Simplify an expression. This performs any static optimization (by rewriting the expression as a different expression).
Overrides:
simplify in interface Instruction
Parameters:
visitor - an expression visitor
Returns:
the simplified expression
Throws:
XPathException - if an error is discovered during expression rewriting

typeCheck

public Expression typeCheck(ExpressionVisitor visitor,
                            ItemType contextItemType)
            throws XPathException
Perform type checking of an expression and its subexpressions. This is the second phase of static optimization.

This checks statically that the operands of the expression have the correct type; if necessary it generates code to do run-time type checking or type conversion. A static type error is reported only if execution cannot possibly succeed, that is, if a run-time type error is inevitable. The call may return a modified form of the expression.

This method is called after all references to functions and variables have been resolved to the declaration of the function or variable. However, the types of such functions and variables may not be accurately known if they have not been explicitly declared.

If the implementation returns a value other than "this", then it is required to ensure that the parent pointer and location information in the returned expression have been set up correctly. It should not rely on the caller to do this, although for historical reasons many callers do so.

Overrides:
typeCheck in interface Expression
Parameters:
visitor - an expression visitor
contextItemType - the static type of "." at the point where this expression is invoked. The parameter is set to null if it is known statically that the context item will be undefined. If the type of the context item is not known statically, the argument is set to Type.ITEM_TYPE
Returns:
the original expression, rewritten to perform necessary run-time type checks, and to perform other type-related optimizations
Throws:
XPathException - if an error is discovered during this phase (typically a type error)