com.saxonica.expr.flwor
Class GroupByClause

java.lang.Object
  net.sf.saxon.expr.flwor.Clause
      com.saxonica.expr.flwor.GroupByClause

public class GroupByClause
extends Clause

This class represents an "group by" clause in a FLWOR expression

Nested Class Summary

static class	GroupByClause.ObjectToBeGrouped Inner class representing the contents of a tuple from the pre-grouping tuple stream; a set of such objects consitutes a group.
class	GroupByClause.TupleComparisonKey Inner class representing a tuple comparison key: that is, an arbitrary object whose equals() and hashCode() methods can be used to test whether two tuples have equivalent grouping keys

Field Summary

Fields inherited from class net.sf.saxon.expr.flwor.Clause

COUNT, FOR, GROUPBYCLAUSE, LET, ORDERBYCLAUSE, WHERE, WINDOW

Constructor Summary

GroupByClause(Configuration config)
Create a group-by clause

Method Summary

GroupByClause	copy()
void	explain(ExpressionPresenter out) Diagnostic print of expression structure.
int	getClauseKey() Get a keyword identifying what kind of clause this is
GroupByClause.TupleComparisonKey	getComparisonKey(Tuple t) Callback to get the comparison key for a tuple.
TupleExpression	getGroupingTupleExpression() Get the tuple expression that evaluates all the grouping variables, returning the values these variables take in the input stream
TuplePull	getPullStream(TuplePull base, XPathContext context) Get a tuple stream that implements the functionality of this clause, taking its input from another tuple stream which this clause modifies
TuplePush	getPushStream(TuplePush destination, XPathContext context) Get a push-mode tuple stream that implements the functionality of this clause, supplying its output to another tuple stream
LocalVariableBinding[]	getRangeVariables() Get the variables bound by this clause
TupleExpression	getRetainedTupleExpression() Get the tuple expression that evaluates all the non-grouping variables, returning the values these variables take in the grouping input stream
void	optimize(ExpressionVisitor visitor, ExpressionVisitor.ContextItemType contextItemType) Optimize any expressions contained within this clause
void	processGroup(List<GroupByClause.ObjectToBeGrouped> group, XPathContext context) Process a group of tuples from the input stream to generate a single tuple in the output stream.
void	processSubExpressions(ExpressionProcessor processor) Process the subexpressions of this clause
void	setComparers(GenericAtomicComparer[] comparers) Set the comparers used for the grouping keys.
void	setGroupingTupleExpression(TupleExpression expr) Set a tuple expression that evaluates all the grouping variables, returning the values these variables take in the input stream
void	setRetainedTupleExpression(TupleExpression expr) Set a tuple expression that evaluates all the non-grouping variables, returning the values these variables take in the grouping input stream
void	setVariableBindings(LocalVariableBinding[] bindings) Set the bindings of new variables created by the grouping clause, which constitute the variables appearing in the output (post-grouping) tuple stream.
String	toString()

Methods inherited from class net.sf.saxon.expr.flwor.Clause

gatherVariableReferences, refineVariableType, typeCheck

Methods inherited from class java.lang.Object

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

Constructor Detail

GroupByClause

public GroupByClause(Configuration config)

Create a group-by clause

Parameters:

config - the Saxon configuration

Method Detail

getClauseKey

public int getClauseKey()

Description copied from class: Clause

Get a keyword identifying what kind of clause this is

Specified by:

getClauseKey in class Clause

Returns:

the kind of clause

copy

public GroupByClause copy()

Specified by:

copy in class Clause

setRetainedTupleExpression

public void setRetainedTupleExpression(TupleExpression expr)

Set a tuple expression that evaluates all the non-grouping variables, returning the values these variables take in the grouping input stream

Parameters:

expr - the tuple expression

getRetainedTupleExpression

public TupleExpression getRetainedTupleExpression()

Get the tuple expression that evaluates all the non-grouping variables, returning the values these variables take in the grouping input stream

Returns:

the tuple expression

optimize

public void optimize(ExpressionVisitor visitor,
                     ExpressionVisitor.ContextItemType contextItemType)
              throws XPathException

Description copied from class: Clause

Optimize any expressions contained within this clause

Overrides:

optimize in class Clause

Parameters:

visitor - the ExpressionVisitor, providing access to static context information

contextItemType - the type of the context item

Throws:

XPathException - if any error is detected

setGroupingTupleExpression

public void setGroupingTupleExpression(TupleExpression expr)

Set a tuple expression that evaluates all the grouping variables, returning the values these variables take in the input stream

Parameters:

expr - the tuple expression

getGroupingTupleExpression

public TupleExpression getGroupingTupleExpression()

Get the tuple expression that evaluates all the grouping variables, returning the values these variables take in the input stream

Returns:

the tuple expression

setVariableBindings

public void setVariableBindings(LocalVariableBinding[] bindings)

Set the bindings of new variables created by the grouping clause, which constitute the variables appearing in the output (post-grouping) tuple stream. There will be one of these for each variable in the input (pre-grouping) stream; by convention the bindings for grouping variables precede the bindings for non-grouping (retained) variables, and the order is preserved.

Parameters:

bindings - the bindings of the variables created in the output stream

getRangeVariables

public LocalVariableBinding[] getRangeVariables()

Get the variables bound by this clause

Overrides:

getRangeVariables in class Clause

Returns:

the variable bindings

setComparers

public void setComparers(GenericAtomicComparer[] comparers)

Set the comparers used for the grouping keys. There is one comparer for each grouping variable

Parameters:

comparers - the comparers for grouping keys.

getPullStream

public TuplePull getPullStream(TuplePull base,
                               XPathContext context)

Get a tuple stream that implements the functionality of this clause, taking its input from another tuple stream which this clause modifies

Specified by:

getPullStream in class Clause

Parameters:

base - the input tuple stream

context - the XPath dynamic evaluation context

Returns:

the output tuple stream

getPushStream

public TuplePush getPushStream(TuplePush destination,
                               XPathContext context)

Get a push-mode tuple stream that implements the functionality of this clause, supplying its output to another tuple stream

Specified by:

getPushStream in class Clause

Parameters:

destination - the output tuple stream

context -

Returns:

the push tuple stream that implements the functionality of this clause of the FLWOR expression

processSubExpressions

public void processSubExpressions(ExpressionProcessor processor)
                           throws XPathException

Process the subexpressions of this clause

Specified by:

processSubExpressions in class Clause

Parameters:

processor - the expression processor used to process the subexpressions

Throws:

XPathException - if any error is detected

explain

public void explain(ExpressionPresenter out)

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

Specified by:

explain in class Clause

Parameters:

out - the expression presenter used to display the structure

toString

public String toString()

Overrides:

toString in class Object

processGroup

public void processGroup(List<GroupByClause.ObjectToBeGrouped> group,
                         XPathContext context)
                  throws XPathException

Process a group of tuples from the input stream to generate a single tuple in the output stream. This method takes a group of tuples as input, and sets all the required variables in the local stack frame as required to deliver this group as the current tuple in the post-grouping stream

Parameters:

group - the group of input tuples

context - the XPath dynamic evaluation context

Throws:

XPathException

getComparisonKey

public GroupByClause.TupleComparisonKey getComparisonKey(Tuple t)

Callback to get the comparison key for a tuple. Two tuples are equal if their comparison keys compare equal using the equals() method.