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
public final class FilterExpression extends BinaryExpression implements ContextSwitchingExpression
A FilterExpression contains a base expression and a filter predicate, which may be an integer expression (positional filter), or a boolean expression (qualifier)

  • Field Details

    • doneReorderingPredicates

      public boolean doneReorderingPredicates

    • FILTERED

      public static final int FILTERED
      See Also:

    • FILTER_PREDICATE

      public static final OperandRole FILTER_PREDICATE

  • Constructor Details

    • FilterExpression

      public FilterExpression(Expression base, Expression filter)
      Constructor
      Parameters:
      base - The base expression to be filtered.
      filter - An expression defining the filter predicate

  • Method Details

    • getOperandRole

      protected OperandRole getOperandRole(int arg)
      Description copied from class: BinaryExpression
      Get the operand role
      Overrides:
      getOperandRole in class BinaryExpression
      Parameters:
      arg - which argument: 0 for the lhs, 1 for the rhs
      Returns:
      the operand role

    • getBase

      public Expression getBase()

    • setBase

      public void setBase(Expression base)

    • disableIndexing

      public void disableIndexing()

    • getFilter

      public Expression getFilter()
      Get the filter expression
      Returns:
      the expression acting as the filter predicate

    • setFilter

      public void setFilter(Expression filter)

    • getExpressionName

      public String getExpressionName()
      Get a name identifying the kind of expression, in terms meaningful to a user.
      Overrides:
      getExpressionName in class Expression
      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.

    • getItemType

      public ItemType getItemType()
      Get the data type of the items returned
      Specified by:
      getItemType in class Expression
      Returns:
      an integer representing the data type

    • getStaticUType

      public UType getStaticUType(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.
      Overrides:
      getStaticUType in class Expression
      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

    • getSelectExpression

      public Expression getSelectExpression()
      Get the base expression
      Specified by:
      getSelectExpression in interface ContextSwitchingExpression
      Returns:
      the base expression being filtered

    • isFilterIsPositional

      public boolean isFilterIsPositional()
      Ask if the filter is positional
      Returns:
      true filter is positional

    • getActionExpression

      public Expression getActionExpression()
      Get the subexpression that is evaluated in the new context
      Specified by:
      getActionExpression in interface ContextSwitchingExpression
      Returns:
      the subexpression evaluated in the context set by the controlling expression

    • isPositional

      public boolean isPositional(TypeHierarchy th)
      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

    • 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

    • isIndependentFilter

      public boolean isIndependentFilter()
      Determine whether the filter is independent of the context item and position

      This 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

    • simplify

      public Expression simplify() throws XPathException
      Simplify an expression
      Overrides:
      simplify in class Expression
      Returns:
      the simplified expression (or the original if unchanged, or if modified in-situ)
      Throws:
      XPathException - if any failure occurs

    • typeCheck

      public Expression typeCheck(ExpressionVisitor visitor, ContextItemStaticInfo contextInfo) throws XPathException
      Type-check the expression
      Overrides:
      typeCheck in class BinaryExpression
      Parameters:
      visitor - the expression visitor
      contextInfo - 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)

    • 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 class BinaryExpression
      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 Type.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)

    • 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 class Expression
      Returns:
      the estimated cost

    • 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 class BinaryExpression
      Returns:
      the implementation method, for example Expression.ITERATE_METHOD or Expression.EVALUATE_METHOD or Expression.PROCESS_METHOD

    • getIntegerBounds

      public IntegerValue[] 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 class Expression
      Returns:
      the lower and upper bounds of integer values in the result, or null to indicate unknown or not applicable.

    • 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.
      Overrides:
      addToPathMap in class Expression
      Parameters:
      pathMap - the PathMap to which the expression should be added
      pathMapNodeSet - 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

    • unordered

      public Expression unordered(boolean retainAllNodes, boolean forStreaming) throws XPathException
      Replace this expression by a simpler expression that delivers the results without regard to order.
      Overrides:
      unordered in class Expression
      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

    • isPositionalFilter

      public static 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.
      Parameters:
      exp - the expression to be examined
      th - the type hierarchy cache
      Returns:
      true if the expression depends on position() or last() explicitly or implicitly

    • computeCardinality

      protected int computeCardinality()
      Get the static cardinality of this expression
      Overrides:
      computeCardinality in class BinaryExpression
      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

    • 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 class BinaryExpression
      Returns:
      the static properties of the expression, as a bit-significant value

    • equals

      public boolean equals(Object other)
      Is this expression the same as another expression?
      Overrides:
      equals in class BinaryExpression
      Parameters:
      other - the expression to be compared with this one
      Returns:
      true if the two expressions are statically equivalent

    • computeHashCode

      protected int computeHashCode()
      get HashCode for comparing two expressions
      Overrides:
      computeHashCode in class BinaryExpression
      Returns:
      the hash code

    • toPattern

      public Pattern toPattern(Configuration config) throws XPathException
      Convert this expression to an equivalent XSLT pattern
      Overrides:
      toPattern in class Expression
      Parameters:
      config - the Saxon configuration
      Returns:
      the equivalent pattern
      Throws:
      XPathException - if conversion is not possible

    • iterate

      public SequenceIterator iterate(XPathContext context) throws XPathException
      Iterate over the results, returning them in the correct order
      Overrides:
      iterate in class Expression
      Parameters:
      context - the dynamic context for the evaluation
      Returns:
      an iterator over the expression results
      Throws:
      XPathException - if any dynamic error occurs

    • copy

      public Expression copy(RebindingMap rebindings)
      Copy an expression. This makes a deep copy.
      Specified by:
      copy in class Expression
      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

    • getStreamerName

      public String getStreamerName()
      Get the (partial) name of a class that supports streaming of this kind of expression
      Overrides:
      getStreamerName in class Expression
      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

    • toString

      public String 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 class BinaryExpression
      Returns:
      the expression as a string in XPath 3.0 syntax

    • toShortString

      public String toShortString()
      Description copied from class: Expression
      Produce a short string identifying the expression for use in error messages
      Overrides:
      toShortString in class BinaryExpression
      Returns:
      a short string, sufficient to identify the expression

    • export

      public void export(ExpressionPresenter out) throws XPathException
      Diagnostic print of expression structure. The abstract expression tree is written to the supplied output destination.
      Specified by:
      export in interface ExportAgent
      Overrides:
      export in class BinaryExpression
      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.

    • setFlags

      public void setFlags(String flags)

    • getElaborator

      public Elaborator getElaborator()
      Make an elaborator for this expression
      Overrides:
      getElaborator in class Expression
      Returns:
      a suitable elaborator