Class ForEachGroup

All Implemented Interfaces:
Serializable, SourceLocator, LocationProvider, SaxonLocator, ContextMappingFunction, EvaluableItem, SequenceIterable, TailCallReturner, SortKeyEvaluator, InstructionInfo, Locator

public class ForEachGroup extends Instruction implements ContextMappingFunction, SortKeyEvaluator
Handler for xsl:for-each-group elements in stylesheet. This is a new instruction defined in XSLT 2.0
See Also:
  • Field Details

  • Constructor Details

    • ForEachGroup

      public ForEachGroup(Expression select, Expression action, byte algorithm, Expression key, StringCollator collator, Expression collationNameExpression, String baseURI, SortKeyDefinition[] sortKeys)
      Create a for-each-group instruction
      Parameters:
      select - the select expression (selects the population to be grouped)
      action - the body of the for-each-group (applied to each group in turn)
      algorithm - one of group-by, group-adjacent, group-starting-with, group-ending-with
      key - expression to evaluate the grouping key
      collator - user for comparing strings
      collationNameExpression - expression that yields the name of the collation to be used
      baseURI - static base URI of the expression
      sortKeys - list of xsl:sort keys for sorting the groups
  • Method Details

    • getInstructionNameCode

      public int getInstructionNameCode()
      Get the name of this instruction for diagnostic and tracing purposes
      Overrides:
      getInstructionNameCode in class Instruction
      Returns:
      the name of the instruction
    • getActionExpression

      public Expression getActionExpression()
      Get the action expression (the content of the for-each-group)
      Returns:
      the body of the xsl:for-each-group instruction
    • getGroupingKey

      public Expression getGroupingKey()
      Get the grouping key expression expression (the group-by or group-adjacent expression, or a PatternSponsor containing the group-starting-with or group-ending-with expression)
      Returns:
      the expression used to calculate grouping keys
    • simplify

      public Expression simplify(ExpressionVisitor visitor) throws XPathException
      Simplify an expression. This performs any static optimization (by rewriting the expression as a different expression).
      Specified by:
      simplify in class Instruction
      Parameters:
      visitor - an expression visitor
      Returns:
      the simplified expression
      Throws:
      XPathException - if an error is discovered during expression rewriting
    • typeCheck

      public Expression typeCheck(ExpressionVisitor visitor, ItemType contextItemType) throws XPathException
      Description copied from class: Expression
      Perform type checking of an expression and its subexpressions. This is the second phase of static optimization.

      This checks statically that the operands of the expression have the correct type; if necessary it generates code to do run-time type checking or type conversion. A static type error is reported only if execution cannot possibly succeed, that is, if a run-time type error is inevitable. The call may return a modified form of the expression.

      This method is called after all references to functions and variables have been resolved to the declaration of the function or variable. However, the types of such functions and variables may not be accurately known if they have not been explicitly declared.

      If the implementation returns a value other than "this", then it is required to ensure that the parent pointer and location information in the returned expression have been set up correctly. It should not rely on the caller to do this, although for historical reasons many callers do so.

      Overrides:
      typeCheck in class Expression
      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 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, ItemType contextItemType) throws XPathException
      Description copied from class: Expression
      Perform optimisation of an expression and its subexpressions. This is the third and final phase of static optimization.

      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 Expression
      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)
    • copy

      public Expression copy()
      Copy an expression. This makes a deep copy.
      Specified by:
      copy in class Expression
      Returns:
      the copy of the original expression
    • getItemType

      public ItemType getItemType(TypeHierarchy th)
      Get the item type of the items returned by evaluating this instruction
      Overrides:
      getItemType in class Instruction
      Parameters:
      th - the type hierarchy cache
      Returns:
      the static item type of the instruction
    • computeDependencies

      public int computeDependencies()
      Compute the dependencies of an expression, as the union of the dependencies of its subexpressions. (This is overridden for path expressions and filter expressions, where the dependencies of a subexpression are not all propogated). This method should be called only once, to compute the dependencies; after that, getDependencies should be used.
      Overrides:
      computeDependencies in class Expression
      Returns:
      the depencies, as a bit-mask
    • createsNewNodes

      public final boolean createsNewNodes()
      Determine whether this instruction creates new nodes. This implementation returns true if the "action" creates new nodes. (Nodes created by the condition can't contribute to the result).
      Overrides:
      createsNewNodes in class Instruction
      Returns:
      true if the instruction creates new nodes (or if it can't be proved that it doesn't)
    • promoteInst

      protected void promoteInst(PromotionOffer offer) throws XPathException
      Handle promotion offers, that is, non-local tree rewrites.
      Overrides:
      promoteInst in class Instruction
      Parameters:
      offer - The type of rewrite being offered
      Throws:
      XPathException
    • iterateSubExpressions

      public Iterator iterateSubExpressions()
      Get all the XPath expressions associated with this instruction (in XSLT terms, the expression present on attributes of the instruction, as distinct from the child instructions in a sequence construction)
      Overrides:
      iterateSubExpressions in class Expression
      Returns:
      an iterator containing the sub-expressions of this expression
    • 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.

      Overrides:
      addToPathMap in class 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.
    • 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
      Overrides:
      hasLoopingSubexpression in class Expression
      Parameters:
      child - the immediate subexpression
      Returns:
      true if the child expression is evaluated repeatedly
    • replaceSubExpression

      public boolean replaceSubExpression(Expression original, Expression replacement)
      Replace one subexpression by a replacement subexpression
      Overrides:
      replaceSubExpression in class Expression
      Parameters:
      original - the original subexpression
      replacement - the replacement subexpression
      Returns:
      true if the original subexpression is found
    • checkPermittedContents

      public void checkPermittedContents(SchemaType parentType, StaticContext env, boolean whole) throws XPathException
      Check that any elements and attributes constructed or returned by this expression are acceptable in the content model of a given complex type. It's always OK to say yes, since the check will be repeated at run-time. The process of checking element and attribute constructors against the content model of a complex type also registers the type of content expected of those constructors, so the static validation can continue recursively.
      Overrides:
      checkPermittedContents in class Expression
      Parameters:
      parentType - the "given complex type": the method is checking that the nodes returned by this expression are acceptable members of the content model of this type
      env - the static context
      whole - if true, we want to check that the value of this expression satisfies the content model as a whole; if false we want to check that the value of the expression is acceptable as one part of the content
      Throws:
      XPathException - if the value delivered by this expression cannot be part of the content model of the given type
    • processLeavingTail

      public TailCall processLeavingTail(XPathContext context) throws XPathException
      Description copied from class: Instruction
      ProcessLeavingTail: called to do the real work of this instruction. This method must be implemented in each subclass. The results of the instruction are written to the current Receiver, which can be obtained via the Controller.
      Specified by:
      processLeavingTail in interface TailCallReturner
      Specified by:
      processLeavingTail in class Instruction
      Parameters:
      context - The dynamic context of the transformation, giving access to the current node, the current variables, etc.
      Returns:
      null if the instruction has completed execution; or a TailCall indicating a function call or template call that is delegated to the caller, to be made after the stack has been unwound so as to save stack space.
      Throws:
      XPathException
    • iterate

      public SequenceIterator iterate(XPathContext context) throws XPathException
      Return an Iterator to iterate over the values of a sequence. The value of every expression can be regarded as a sequence, so this method is supported for all expressions. This default implementation relies on the process() method: it "pushes" the results of the instruction to a sequence in memory, and then iterates over this in-memory sequence.

      In principle instructions should implement a pipelined iterate() method that avoids the overhead of intermediate storage.

      Specified by:
      iterate in interface SequenceIterable
      Overrides:
      iterate in class Instruction
      Parameters:
      context - supplies the context for evaluation
      Returns:
      a SequenceIterator that can be used to iterate over the result of the expression
      Throws:
      XPathException - if any dynamic error occurs evaluating the expression
    • map

      public SequenceIterator map(XPathContext context) throws XPathException
      Map one item to a sequence.
      Specified by:
      map in interface ContextMappingFunction
      Parameters:
      context - The processing context. This is supplied only for mapping constructs that set the context node, position, and size. Otherwise it is null.
      Returns:
      either (a) a SequenceIterator over the sequence of items that the supplied input item maps to, or (b) an Item if it maps to a single item, or (c) null if it maps to an empty sequence.
      Throws:
      XPathException
    • evaluateSortKey

      public Item evaluateSortKey(int n, XPathContext c) throws XPathException
      Callback for evaluating the sort keys
      Specified by:
      evaluateSortKey in interface SortKeyEvaluator
      Throws:
      XPathException
    • explain

      public void explain(ExpressionPresenter out)
      Diagnostic print of expression structure. The abstract expression tree is written to the supplied output destination.
      Specified by:
      explain in class Expression
      Parameters:
      out - the expression presenter used to display the structure