org.basex.query.flwor

Class Group

java.lang.Object

org.basex.data.ExprInfo

org.basex.query.expr.Expr

org.basex.query.expr.ParseExpr

org.basex.query.flwor.Group

public final class Group
extends ParseExpr

Implementation of the group by clause.

Author:

BaseX Team 2005-12, BSD License, Michael Seiferle

Nested Class Summary

Nested Classes

Modifier and Type	Class and Description
static class	Group.Spec Grouping spec.

Nested classes/interfaces inherited from class org.basex.query.expr.Expr

Expr.Use

Field Summary

Fields inherited from class org.basex.query.expr.ParseExpr

input, size, type

Constructor Summary

Constructors

Constructor and Description
Group(InputInfo ii, Group.Spec[] gb, Var[][] ng) Constructor.

Method Summary

Methods

Modifier and Type	Method and Description
Expr	comp(QueryContext ctx) Compiles and optimizes the expression, assigns data types and cardinalities.
int	count(Var v) Counts how often the specified variable is used by an expression.
Iter	iter(QueryContext ctx) Evaluates the expression and returns an iterator on the resulting items.
void	plan(Serializer ser) Serializes the expression tree.
boolean	removable(Var v) Checks if the specified variable is replaceable by a context item.
Expr	remove(Var v) Substitutes all VarRef expressions for the given variable by a Context reference.
java.lang.String	toString()
boolean	uses(Expr.Use use) Indicates if an expression uses the specified type or operation.

Methods inherited from class org.basex.query.expr.ParseExpr

checkBln, checkColl, checkCreate, checkCtx, checkDbl, checkDBNode, checkEStr, checkEStr, checkIO, checkItem, checkItr, checkItr, checkMap, checkNode, checkNoEmpty, checkStr, checkType, checkUp, checkUp, checkWrite, compBln, ebv, item, optPre, preEval, size, test, type, value

Methods inherited from class org.basex.query.expr.Expr

addText, compEbv, hasFreeVars, indexAccessible, indexEquivalent, isEmpty, isFunction, isItem, isVacuous, isValue, iterable, markTailCalls, sameAs

Methods inherited from class org.basex.data.ExprInfo

description, info

Methods inherited from class java.lang.Object

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

Constructor Detail

Group

public Group(InputInfo ii,
     Group.Spec[] gb,
     Var[][] ng)

Constructor.

Parameters:

ii - input info

gb - group by expression

ng - non-grouping variables and their copies

Method Detail

comp

public Expr comp(QueryContext ctx)
          throws QueryException

Description copied from class: Expr

Compiles and optimizes the expression, assigns data types and cardinalities.

Specified by:

comp in class Expr

Parameters:

ctx - query context

Returns:

optimized expression

Throws:

QueryException - query exception

iter

public Iter iter(QueryContext ctx)

Description copied from class: Expr

Evaluates the expression and returns an iterator on the resulting items. If this method is not overwritten, Expr.item(org.basex.query.QueryContext, org.basex.util.InputInfo) must be implemented by an expression, as it may be called by this method.

Overrides:

iter in class ParseExpr

Parameters:

ctx - query context

Returns:

resulting item

uses

public boolean uses(Expr.Use use)

Description copied from class: Expr

Indicates if an expression uses the specified type or operation. This method is called by numerous Expr.comp(org.basex.query.QueryContext) methods to test the properties of sub-expressions. It will return true as soon as at least one test is successful.

Specified by:

uses in class Expr

Parameters:

use - type/operation to be found

Returns:

result of check

count

public int count(Var v)

Description copied from class: Expr

Counts how often the specified variable is used by an expression. This method is called by:

• GFLWOR.comp(org.basex.query.QueryContext) to rewrite where clauses as predicates and remove statically bound or unused clauses
• GFLWOR.compHoist(org.basex.query.QueryContext) to hoist independent variables

Specified by:

count in class Expr

Parameters:

v - variable to be checked

Returns:

number of occurrences

removable

public boolean removable(Var v)

Description copied from class: Expr

Checks if the specified variable is replaceable by a context item. The following tests might return false:

• Preds.removable(org.basex.query.util.Var), if one of the variables is used within a predicate.
• MixedPath.removable(org.basex.query.util.Var), if the variable occurs within the path.
• removable(org.basex.query.util.Var), as the group by expression depends on variable references.

This method is called by GFLWOR.comp(org.basex.query.QueryContext) to rewrite where clauses into predicates.

Specified by:

removable in class Expr

Parameters:

v - variable to be replaced

Returns:

result of check

remove

public Expr remove(Var v)

Description copied from class: Expr

Substitutes all VarRef expressions for the given variable by a Context reference. This method is called by GFLWOR.comp(org.basex.query.QueryContext) to rewrite where clauses as predicates.

Specified by:

remove in class Expr

Parameters:

v - variable to be replaced

Returns:

new expression

plan

public void plan(Serializer ser)
          throws java.io.IOException

Description copied from class: ExprInfo

Serializes the expression tree.

Specified by:

plan in class ExprInfo

Parameters:

ser - serializer

Throws:

java.io.IOException - I/O exception

toString

public java.lang.String toString()

Specified by:

toString in class ExprInfo