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## net.sf.saxon.trans
Class KeyManager

    java.lang.Object
      net.sf.saxon.trans.KeyManager

All Implemented Interfaces:
  java.io.Serializable

    public class KeyManager

extends java.lang.Object
implements java.io.Serializable

KeyManager manages the set of key definitions in a stylesheet, and the indexes associated with these key definitions. It handles xsl:sort-key as well as xsl:key definitions.

The memory management in this class is subtle, with extensive use of weak references. The idea is that an index should continue to exist in memory so long as both the compiled stylesheet and the source document exist in memory: if either is removed, the index should go too. The document itself holds no reference to the index. The compiled stylesheet (which owns the KeyManager) holds a weak reference to the index. The index, of course, holds strong references to the nodes in the document. The Controller holds a strong reference to the list of indexes used for each document, so that indexes remain in memory for the duration of a transformation even if the documents themselves are garbage collected.

Potentially there is a need for more than one index for a given key name, depending on the primitive type of the value provided to the key() function. An index is built corresponding to the type of the requested value; if subsequently the key() function is called with the same name and a different type of value, then a new index is built.

For XSLT-defined keys, equality matching follows the rules of the eq operator, which means that untypedAtomic values are treated as strings. In backwards compatibility mode, all values are converted to strings.

This class is also used for internal indexes constructed (a) to support the idref() function, and (b) (in Saxon-SA only) to support filter expressions of the form /a/b/c[d=e], where the path expression being filtered must be a single-document context-free path rooted at a document node, where exactly one of d and e must be dependent on the focus, and where certain other conditions apply such as the filter predicate not being positional. The operator in this case may be either "=" or "eq". If it is "eq", then the semantics are very similar to xsl:key indexes, except that use of non-comparable types gives an error rather than a non-match. If the operator is "=", however, then the rules for handling untypedAtomic values are different: these must be converted to the type of the other operand. In this situation the following rules apply. Assume that the predicate is [use=value], where use is dependent on the focus (the indexed value), and value is the sought value.

- If value is a type other than untypedAtomic, say T, then we build an index for type T, in which any untypedAtomic values that arise in evaluating "use" are converted to type T. A conversion failure results in an error. A value of a type that is not comparable to T also results in an error.
- If value is untypedAtomic, then we build an index for every type actually encountered in evaluating the use expression (treating untypedAtomic as string), and then search each of these indexes. (Note that it is not an error if the use expression returns a mixture of say numbers and dates, provided that the sought value is untypedAtomic).

Author:
  Michael H. Kay
See Also:
  Serialized Form

Constructor Summary
`KeyManager(Configuration config)` Create a KeyManager and initialise variables

Method Summary
`void` | `addKeyDefinition(StructuredQName keyName, KeyDefinition keydef, Configuration config)` Register a key definition.
`void` | `clearDocumentIndexes(DocumentInfo doc)` Clear all the indexes for a given document.
`void` | `explainKeys(ExpressionPresenter out)` Diagnostic output explaining the keys
`KeyDefinitionSet` | `getKeyDefinitionSet(StructuredQName qName)` Get all the key definitions that match a particular name
`int` | `getNumberOfKeyDefinitions()` Get the number of distinctly-named key definitions
`void` | `preRegisterKeyDefinition(StructuredQName keyName)` Pre-register a key definition.
`SequenceIterator` | `selectByKey(KeyDefinitionSet keySet, DocumentInfo doc, AtomicValue soughtValue, XPathContext context)` Get the nodes with a given key value
`SequenceIterator` | `selectByKey(StructuredQName keyName, DocumentInfo doc, AtomicValue soughtValue, XPathContext context)` Get the nodes with a given key value.

Methods inherited from class java.lang.Object
`clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait`

Constructor Detail

### KeyManager

    public KeyManager(Configuration config)

  Create a KeyManager and initialise variables

  Parameters:
    `config` - the Saxon configuration

Method Detail

### preRegisterKeyDefinition

    public void preRegisterKeyDefinition(StructuredQName keyName)

  Pre-register a key definition. This simply registers that a key with a given name exists, without providing any details.

  Parameters:
    `keyName` - the name of the key to be pre-registered

### addKeyDefinition

    public void addKeyDefinition(StructuredQName keyName,
                                 KeyDefinition keydef,
                                 Configuration config)
                          throws XPathException

  Register a key definition. Note that multiple key definitions with the same name are allowed

  Parameters:
    `keyName` - Structured QName representing the name of the key
    `keydef` - The details of the key's definition
    `config` - The configuration
  Throws:
    `XPathException` - if this key definition is inconsistent with existing key definitions having the same name

### getKeyDefinitionSet

    public KeyDefinitionSet getKeyDefinitionSet(StructuredQName qName)

  Get all the key definitions that match a particular name

  Parameters:
    `qName` - The name of the required key
  Returns:
    The set of key definitions of the named key if there are any, or null otherwise.

### selectByKey

    public SequenceIterator selectByKey(StructuredQName keyName,
                                        DocumentInfo doc,
                                        AtomicValue soughtValue,
                                        XPathContext context)
                                 throws XPathException

  Get the nodes with a given key value. This method is called from XQuery compiled code

  Parameters:
    `keyName` - key name used in the call to the key() function
    `doc` - The source document in question
    `soughtValue` - The required key value
    `context` - The dynamic context, needed only the first time when the key is being built
  Returns:
    an iteration of the selected nodes, always in document order with no duplicates
  Throws:
    `XPathException`

### selectByKey

    public SequenceIterator selectByKey(KeyDefinitionSet keySet,
                                        DocumentInfo doc,
                                        AtomicValue soughtValue,
                                        XPathContext context)
                                 throws XPathException

  Get the nodes with a given key value

  Parameters:
    `keySet` - The set of key definitions identified by the key name used in the call to the key() function
    `doc` - The source document in question
    `soughtValue` - The required key value
    `context` - The dynamic context, needed only the first time when the key is being built
  Returns:
    an iteration of the selected nodes, always in document order with no duplicates
  Throws:
    `XPathException`

### clearDocumentIndexes

    public void clearDocumentIndexes(DocumentInfo doc)

  Clear all the indexes for a given document. This is currently done whenever updates are applied to the document, because updates can potentially invalidate the indexes.

  Parameters:
    `doc` - the document whose indexes are to be invalidated

### getNumberOfKeyDefinitions

    public int getNumberOfKeyDefinitions()

  Get the number of distinctly-named key definitions

  Returns:
    the number of key definition sets (where the key definitions in one set share the same name)

### explainKeys

    public void explainKeys(ExpressionPresenter out)

  Diagnostic output explaining the keys

  Parameters:
    `out` - the expression presenter that will display the information

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Copyright (c) Saxonica Limited. All rights reserved.