net.sf.saxon.sort

Class SortExpression

public class SortExpression extends Expression implements SortKeyEvaluator

Expression equivalent to the imaginary syntax expr sortby (sort-key)+
Constructor Summary
SortExpression(Expression select, SortKeyDefinition[] sortKeys)
Create a sort expression
Method Summary
PathMap.PathMapNodeSetaddToPathMap(PathMap pathMap, PathMap.PathMapNodeSet pathMapNodeSet)
Add a representation of this expression to a PathMap.
intcomputeCardinality()
Determine the static cardinality
intcomputeSpecialProperties()
Get the static properties of this expression (other than its type).
Expressioncopy()
Copy an expression.
ItemevaluateSortKey(int n, XPathContext c)
Callback for evaluating the sort keys
voidexplain(ExpressionPresenter out)
Diagnostic print of expression structure.
ExpressiongetBaseExpression()
Get the expression defining the sequence being sorted
ItemTypegetItemType(TypeHierarchy th)
Determine the data type of the items returned by the expression, if possible
booleanhasLoopingSubexpression(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
booleanisSortKey(Expression child)
Test whether a given expression is one of the sort keys
SequenceIteratoriterate(XPathContext context)
Enumerate the results of the expression
Iterator<Expression>iterateSameFocusSubExpressions()
Get the immediate sub-expressions of this expression that are evaluated with the same focus (context item, position, and size) as the parent expression.
Iterator<Expression>iterateSubExpressions()
Get the immediate sub-expressions of this expression.
Expressionoptimize(ExpressionVisitor visitor, ItemType contextItemType)
Perform optimisation of an expression and its subexpressions.
Expressionpromote(PromotionOffer offer, Expression parent)
Offer promotion for this subexpression.
booleanreplaceSubExpression(Expression original, Expression replacement)
Replace one subexpression by a replacement subexpression
Expressionsimplify(ExpressionVisitor visitor)
Simplify an expression
ExpressiontypeCheck(ExpressionVisitor visitor, ItemType contextItemType)
Type-check the expression

Constructor Detail

SortExpression

public SortExpression(Expression select, SortKeyDefinition[] sortKeys)
Create a sort expression

Parameters: select the expression whose result is to be sorted sortKeys the set of sort key definitions to be used, in major to minor order

Method Detail

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.

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.

computeCardinality

public int computeCardinality()
Determine the static cardinality

computeSpecialProperties

public int computeSpecialProperties()
Get the static properties of this expression (other than its type). The result is bit-significant. These properties are used for optimizations. In general, if property bit is set, it is true, but if it is unset, the value is unknown.

copy

public Expression copy()
Copy an expression. This makes a deep copy.

Returns: the copy of the original expression

evaluateSortKey

public Item evaluateSortKey(int n, XPathContext c)
Callback for evaluating the sort keys

explain

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

getBaseExpression

public Expression getBaseExpression()
Get the expression defining the sequence being sorted

Returns: the expression whose result is to be sorted

getItemType

public ItemType getItemType(TypeHierarchy th)
Determine the data type of the items returned by the expression, if possible

Parameters: th the type hierarchy cache

Returns: a value such as Type.STRING, Type.BOOLEAN, Type.NUMBER, Type.NODE, or Type.ITEM (meaning not known in advance)

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

Parameters: child the immediate subexpression

Returns: true if the child expression is evaluated repeatedly

isSortKey

public boolean isSortKey(Expression child)
Test whether a given expression is one of the sort keys

Parameters: child the given expression

Returns: true if the given expression is one of the sort keys

iterate

public SequenceIterator iterate(XPathContext context)
Enumerate the results of the expression

iterateSameFocusSubExpressions

public Iterator<Expression> iterateSameFocusSubExpressions()
Get the immediate sub-expressions of this expression that are evaluated with the same focus (context item, position, and size) as the parent expression. The default implementation returns all the sub-expressions of this expression

Returns: an iterator containing those sub-expressions of this expression that are evaluated with the same focus as the parent expression

iterateSubExpressions

public Iterator<Expression> iterateSubExpressions()
Get the immediate sub-expressions of this expression. Default implementation returns a zero-length array, appropriate for an expression that has no sub-expressions.

Returns: an iterator containing the sub-expressions of this expression

optimize

public Expression optimize(ExpressionVisitor visitor, ItemType contextItemType)
Perform optimisation of an expression and its subexpressions.

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.

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 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)

promote

public Expression promote(PromotionOffer offer, Expression parent)
Offer promotion for this subexpression. The offer will be accepted if the subexpression is not dependent on the factors (e.g. the context item) identified in the PromotionOffer. By default the offer is not accepted - this is appropriate in the case of simple expressions such as constant values and variable references where promotion would give no performance advantage. This method is always called at compile time.

Parameters: offer details of the offer, for example the offer to move expressions that don't depend on the context to an outer level in the containing expression parent

Returns: if the offer is not accepted, return this expression unchanged. Otherwise return the result of rewriting the expression to promote this subexpression

Throws: net.sf.saxon.trans.XPathException if any error is detected

replaceSubExpression

public boolean replaceSubExpression(Expression original, Expression replacement)
Replace one subexpression by a replacement subexpression

Parameters: original the original subexpression replacement the replacement subexpression

Returns: true if the original subexpression is found

simplify

public Expression simplify(ExpressionVisitor visitor)
Simplify an expression

Parameters: visitor an expression visitor

typeCheck

public Expression typeCheck(ExpressionVisitor visitor, ItemType contextItemType)
Type-check the expression