Package net.sf.saxon.expr
Class FilterExpression
java.lang.Object
net.sf.saxon.expr.Expression
net.sf.saxon.expr.BinaryExpression
net.sf.saxon.expr.FilterExpression
- All Implemented Interfaces:
ContextOriginator
,ContextSwitchingExpression
,ExportAgent
,Locatable
,IdentityComparable
,Traceable
A FilterExpression contains a base expression and a filter predicate, which may be an
integer expression (positional filter), or a boolean expression (qualifier)
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Nested Class Summary
Nested ClassesModifier and TypeClassDescriptionstatic class
Elaborator for a filter expression -
Field Summary
FieldsFields inherited from class net.sf.saxon.expr.BinaryExpression
operator
Fields inherited from class net.sf.saxon.expr.Expression
EFFECTIVE_BOOLEAN_VALUE, EVALUATE_METHOD, ITEM_FEED_METHOD, ITERATE_METHOD, MAX_COST, MAX_SEQUENCE_LENGTH, MAX_STRING_LENGTH, PROCESS_METHOD, staticProperties, UNBOUNDED_LOWER, UNBOUNDED_UPPER, UPDATE_METHOD, WATCH_METHOD
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Constructor Summary
Constructors -
Method Summary
Modifier and TypeMethodDescriptionaddToPathMap
(PathMap pathMap, PathMap.PathMapNodeSet pathMapNodeSet) Add a representation of this expression to a PathMap.protected int
Get the static cardinality of this expressionprotected int
get HashCode for comparing two expressionsprotected int
Get the static properties of this expression (other than its type).copy
(RebindingMap rebindings) Copy an expression.void
boolean
Is this expression the same as another expression?void
Diagnostic print of expression structure.Get the subexpression that is evaluated in the new contextgetBase()
double
getCost()
Return the estimated cost of evaluating an expression.Make an elaborator for this expressionGet a name identifying the kind of expression, in terms meaningful to a user.Get the filter expressionint
An implementation of Expression must provide at least one of the methods evaluateItem(), iterate(), or process().For an expression that returns an integer or a sequence of integers, get a lower and upper bound on the values of the integers that may be returned, from static analysis.Get the data type of the items returnedprotected OperandRole
getOperandRole
(int arg) Get the operand roleGet the base expressiongetStaticUType
(UType contextItemType) Get the static type of the expression as a UType, following precisely the type inference rules defined in the XSLT 3.0 specification.Get the (partial) name of a class that supports streaming of this kind of expressionboolean
Ask if the filter is positionalboolean
Determine whether the filter is independent of the context item and positionboolean
Determine if the filter is positionalstatic boolean
isPositionalFilter
(Expression exp, TypeHierarchy th) Determine whether an expression, when used as a filter, is potentially positional; that is, where it either contains a call on position() or last(), or where it is capable of returning a numeric result.boolean
Test if the filter always returns a singleton boolean.iterate
(XPathContext context) Iterate over the results, returning them in the correct orderoptimize
(ExpressionVisitor visitor, ContextItemStaticInfo contextItemType) Perform optimisation of an expression and its subexpressions.void
setBase
(Expression base) void
setFilter
(Expression filter) void
simplify()
Simplify an expressiontoPattern
(Configuration config) Convert this expression to an equivalent XSLT patternProduce a short string identifying the expression for use in error messagestoString()
The toString() method for an expression attempts to give a representation of the expression in an XPath-like form, but there is no guarantee that the syntax will actually be true XPath.typeCheck
(ExpressionVisitor visitor, ContextItemStaticInfo contextInfo) Type-check the expressionunordered
(boolean retainAllNodes, boolean forStreaming) Replace this expression by a simpler expression that delivers the results without regard to order.Methods inherited from class net.sf.saxon.expr.BinaryExpression
displayOperator, explainExtraAttributes, getLhs, getLhsExpression, getOperator, getRhs, getRhsExpression, isAssociative, isCommutative, isInverse, operands, setFlattened, setLhsExpression, setRhsExpression, tag
Methods inherited from class net.sf.saxon.expr.Expression
adoptChildExpression, allowExtractingCommonSubexpressions, checkedOperands, checkForUpdatingSubexpressions, checkPermittedContents, computeDependencies, computeStaticProperties, dispatchTailCall, dynamicError, effectiveBooleanValue, evaluateAsString, evaluateItem, explain, getCardinality, getConfiguration, getDependencies, getEvaluationMethod, getExtraProperty, getIntrinsicDependencies, getLocalRetainedStaticContext, getLocation, getNetCost, getObjectName, getPackageData, getParentExpression, getProperties, getProperty, getRetainedStaticContext, getScopingExpression, getSlotsUsed, getSpecialProperties, getStaticBaseURI, getStaticBaseURIString, getStaticType, getTracingTag, hasCompatibleStaticContext, hashCode, hasSpecialProperty, hasVariableBinding, identityHashCode, implementsStaticTypeCheck, isCallOn, isEqual, isIdentical, isInstruction, isLiftable, isMultiThreaded, isStaticPropertiesKnown, isSubtreeExpression, isUpdatingExpression, isVacuousExpression, makeElaborator, markTailFunctionCalls, operandList, operandSparseList, optimizeChildren, prepareForStreaming, process, resetLocalStaticProperties, restoreParentPointers, setEvaluationMethod, setExtraProperty, setFiltered, setLocation, setParentExpression, setRetainedStaticContext, setRetainedStaticContextLocally, setRetainedStaticContextThoroughly, setStaticProperty, simplifyChildren, staticTypeCheck, supportsLazyEvaluation, suppressValidation, typeCheckChildren, typeError, verifyParentPointers, withLocation
Methods inherited from class java.lang.Object
clone, finalize, getClass, notify, notifyAll, wait, wait, wait
Methods inherited from interface net.sf.saxon.trace.Traceable
gatherProperties
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Field Details
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Constructor Details
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Method Details
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getOperandRole
Description copied from class:BinaryExpression
Get the operand role- Overrides:
getOperandRole
in classBinaryExpression
- Parameters:
arg
- which argument: 0 for the lhs, 1 for the rhs- Returns:
- the operand role
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getBase
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setBase
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disableIndexing
public void disableIndexing() -
getFilter
Get the filter expression- Returns:
- the expression acting as the filter predicate
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setFilter
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getExpressionName
Get a name identifying the kind of expression, in terms meaningful to a user.- Overrides:
getExpressionName
in classExpression
- Returns:
- a name identifying the kind of expression, in terms meaningful to a user. The name will always be in the form of a lexical XML QName, and should match the name used in explain() output displaying the expression.
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getItemType
Get the data type of the items returned- Specified by:
getItemType
in classExpression
- Returns:
- an integer representing the data type
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getStaticUType
Get the static type of the expression as a UType, following precisely the type inference rules defined in the XSLT 3.0 specification.- Overrides:
getStaticUType
in classExpression
- Parameters:
contextItemType
- the static type of the context item- Returns:
- the static item type of the expression according to the XSLT 3.0 defined rules
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getSelectExpression
Get the base expression- Specified by:
getSelectExpression
in interfaceContextSwitchingExpression
- Returns:
- the base expression being filtered
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isFilterIsPositional
public boolean isFilterIsPositional()Ask if the filter is positional- Returns:
- true filter is positional
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getActionExpression
Get the subexpression that is evaluated in the new context- Specified by:
getActionExpression
in interfaceContextSwitchingExpression
- Returns:
- the subexpression evaluated in the context set by the controlling expression
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isPositional
Determine if the filter is positional- Parameters:
th
- the Type Hierarchy (for cached access to type information)- Returns:
- true if the value of the filter depends on the position of the item against which it is evaluated
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isSimpleBooleanFilter
public boolean isSimpleBooleanFilter()Test if the filter always returns a singleton boolean.This information is available only after typeCheck() has been called.
- Returns:
- true if the filter is a simple boolean expression
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isIndependentFilter
public boolean isIndependentFilter()Determine whether the filter is independent of the context item and positionThis information is available only after typeCheck() has been called.
- Returns:
- true if the filter is a numeric value that does not depend on the context item or position
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simplify
Simplify an expression- Overrides:
simplify
in classExpression
- Returns:
- the simplified expression (or the original if unchanged, or if modified in-situ)
- Throws:
XPathException
- if any failure occurs
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typeCheck
public Expression typeCheck(ExpressionVisitor visitor, ContextItemStaticInfo contextInfo) throws XPathException Type-check the expression- Overrides:
typeCheck
in classBinaryExpression
- Parameters:
visitor
- the expression visitorcontextInfo
- return the expression after type-checking (potentially modified to add run-time checks and/or conversions)- 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)
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optimize
public Expression optimize(ExpressionVisitor visitor, ContextItemStaticInfo contextItemType) throws XPathException 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.
- Overrides:
optimize
in classBinaryExpression
- Parameters:
visitor
- an expression visitorcontextItemType
- 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 toType.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)
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getCost
public double getCost()Return the estimated cost of evaluating an expression. This is a very crude measure based on the syntactic form of the expression (we have no knowledge of data values). We take the cost of evaluating a simple scalar comparison or arithmetic expression as 1 (one), and we assume that a sequence has length 5. The resulting estimates may be used, for example, to reorder the predicates in a filter expression so cheaper predicates are evaluated first.- Overrides:
getCost
in classExpression
- Returns:
- the estimated cost
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getImplementationMethod
public int getImplementationMethod()An implementation of Expression must provide at least one of the methods evaluateItem(), iterate(), or process(). This method indicates which of these methods is provided directly. The other methods will always be available indirectly, using an implementation that relies on one of the other methods.- Overrides:
getImplementationMethod
in classBinaryExpression
- Returns:
- the implementation method, for example
Expression.ITERATE_METHOD
orExpression.EVALUATE_METHOD
orExpression.PROCESS_METHOD
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getIntegerBounds
For an expression that returns an integer or a sequence of integers, get a lower and upper bound on the values of the integers that may be returned, from static analysis. The default implementation returns null, meaning "unknown" or "not applicable". Other implementations return an array of two IntegerValue objects, representing the lower and upper bounds respectively. The values UNBOUNDED_LOWER and UNBOUNDED_UPPER are used by convention to indicate that the value may be arbitrarily large. The values MAX_STRING_LENGTH and MAX_SEQUENCE_LENGTH are used to indicate values limited by the size of a string or the size of a sequence.- Overrides:
getIntegerBounds
in classExpression
- Returns:
- the lower and upper bounds of integer values in the result, or null to indicate unknown or not applicable.
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addToPathMap
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.- Overrides:
addToPathMap
in classExpression
- Parameters:
pathMap
- the PathMap to which the expression should be addedpathMapNodeSet
- the PathMapNodeSet to which the paths embodied in this expression should be added- 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
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unordered
Replace this expression by a simpler expression that delivers the results without regard to order.- Overrides:
unordered
in classExpression
- Parameters:
retainAllNodes
- set to true if the result must contain exactly the same nodes as the original; set to false if the result can eliminate (or introduce) duplicates.forStreaming
- set to true if optimizing for streaming- Returns:
- an expression that delivers the same nodes in a more convenient order
- Throws:
XPathException
- if the rewrite fails
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isPositionalFilter
Determine whether an expression, when used as a filter, is potentially positional; that is, where it either contains a call on position() or last(), or where it is capable of returning a numeric result.- Parameters:
exp
- the expression to be examinedth
- the type hierarchy cache- Returns:
- true if the expression depends on position() or last() explicitly or implicitly
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computeCardinality
protected int computeCardinality()Get the static cardinality of this expression- Overrides:
computeCardinality
in classBinaryExpression
- Returns:
- the cardinality. The method attempts to determine the case where the filter predicate is guaranteed to select at most one item from the sequence being filtered
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computeSpecialProperties
protected 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.- Overrides:
computeSpecialProperties
in classBinaryExpression
- Returns:
- the static properties of the expression, as a bit-significant value
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equals
Is this expression the same as another expression?- Overrides:
equals
in classBinaryExpression
- Parameters:
other
- the expression to be compared with this one- Returns:
- true if the two expressions are statically equivalent
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computeHashCode
protected int computeHashCode()get HashCode for comparing two expressions- Overrides:
computeHashCode
in classBinaryExpression
- Returns:
- the hash code
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toPattern
Convert this expression to an equivalent XSLT pattern- Overrides:
toPattern
in classExpression
- Parameters:
config
- the Saxon configuration- Returns:
- the equivalent pattern
- Throws:
XPathException
- if conversion is not possible
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iterate
Iterate over the results, returning them in the correct order- Overrides:
iterate
in classExpression
- Parameters:
context
- the dynamic context for the evaluation- Returns:
- an iterator over the expression results
- Throws:
XPathException
- if any dynamic error occurs
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copy
Copy an expression. This makes a deep copy.- Specified by:
copy
in classExpression
- Parameters:
rebindings
- a mutable list of (old binding, new binding) pairs that is used to update the bindings held in any local variable references that are copied.- Returns:
- the copy of the original expression
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getStreamerName
Get the (partial) name of a class that supports streaming of this kind of expression- Overrides:
getStreamerName
in classExpression
- Returns:
- the partial name of a class that can be instantiated to provide streaming support in Saxon-EE, or null if there is no such class
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toString
The toString() method for an expression attempts to give a representation of the expression in an XPath-like form, but there is no guarantee that the syntax will actually be true XPath. In the case of XSLT instructions, the toString() method gives an abstracted view of the syntax- Overrides:
toString
in classBinaryExpression
- Returns:
- the expression as a string in XPath 3.0 syntax
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toShortString
Description copied from class:Expression
Produce a short string identifying the expression for use in error messages- Overrides:
toShortString
in classBinaryExpression
- Returns:
- a short string, sufficient to identify the expression
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export
Diagnostic print of expression structure. The abstract expression tree is written to the supplied output destination.- Specified by:
export
in interfaceExportAgent
- Overrides:
export
in classBinaryExpression
- Parameters:
out
- the ExpressionPresenter to be used- Throws:
XPathException
- if the export fails, for example if an expression is found that won't work in the target environment.
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setFlags
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getElaborator
Make an elaborator for this expression- Overrides:
getElaborator
in classExpression
- Returns:
- a suitable elaborator
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