org.basex.query.expr

Class Context

java.lang.Object

org.basex.data.ExprInfo

org.basex.query.expr.Expr

org.basex.query.expr.ParseExpr

org.basex.query.expr.Simple

org.basex.query.expr.Context

public final class Context
extends Simple

Context item.

Author:

BaseX Team 2005-12, BSD License, Christian Gruen

Nested Class Summary

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
Context(InputInfo ii) Constructor.

Method Summary

Methods

Modifier and Type	Method and Description
Expr	addText(QueryContext ctx) Optionally adds a text node to an expression for potential index rewriting.
Expr	comp(QueryContext ctx) Compiles and optimizes the expression, assigns data types and cardinalities.
Item	item(QueryContext ctx, InputInfo ii) Evaluates the expression and returns the resulting item or a null reference, if the expression yields an empty sequence.
Iter	iter(QueryContext ctx) Evaluates the expression and returns an iterator on the resulting items.
boolean	removable(Var v) Checks if the specified variable is replaceable by a context item.
boolean	sameAs(Expr cmp) Compares the current and specified expression for equality.
java.lang.String	toString()
boolean	uses(Expr.Use u) Indicates if an expression uses the specified type or operation.
Value	value(QueryContext ctx) Evaluates the expression and returns the resulting value.

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

count, plan, remove

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, optPre, preEval, size, test, type

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

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

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

Context

public Context(InputInfo ii)

Constructor.

Parameters:

ii - input info

Method Detail

comp

public Expr comp(QueryContext ctx)

Description copied from class: Expr

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

Overrides:

comp in class Simple

Parameters:

ctx - query context

Returns:

optimized expression

iter

public Iter iter(QueryContext ctx)
          throws QueryException

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

Throws:

QueryException - query exception

value

public Value value(QueryContext ctx)
            throws QueryException

Description copied from class: Expr

Evaluates the expression and returns the resulting value.

Overrides:

value in class ParseExpr

Parameters:

ctx - query context

Returns:

iterator

Throws:

QueryException - query exception

item

public Item item(QueryContext ctx,
        InputInfo ii)
          throws QueryException

Description copied from class: Expr

Evaluates the expression and returns the resulting item or a null reference, if the expression yields an empty sequence. If this method is not overwritten, Expr.iter(org.basex.query.QueryContext) must be implemented by an expression, as it may be called by this method.

Overrides:

item in class ParseExpr

Parameters:

ctx - query context

ii - input info

Returns:

iterator

Throws:

QueryException - query exception

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.
• Group.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.

Overrides:

removable in class Simple

Parameters:

v - variable to be replaced

Returns:

result of check

addText

public Expr addText(QueryContext ctx)

Description copied from class: Expr

Optionally adds a text node to an expression for potential index rewriting.

Overrides:

addText in class Expr

Parameters:

ctx - query context

Returns:

expression

uses

public boolean uses(Expr.Use u)

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.

Overrides:

uses in class Simple

Parameters:

u - type/operation to be found

Returns:

result of check

sameAs

public boolean sameAs(Expr cmp)

Description copied from class: Expr

Compares the current and specified expression for equality.

Overrides:

sameAs in class Expr

Parameters:

cmp - expression to be compared

Returns:

result of check

toString

public java.lang.String toString()

Specified by:

toString in class ExprInfo