public class MultiIndex extends Object
A MultiIndex handles a single "use" expression, for a single population.
The class is used to support a variety of indexes: indexes to support the saxon:index() and saxon:find extension functions; and indexes over the value of a variable, as determined by the Saxon-EE optimizer.
The class supports two kinds of equality matching. In ConvertUntypedToOther mode, corresponding to the XPath "=" operator, an untyped value is converted to the type of the other item, so the double 5e0 will match the untypedAtomic value "5". In ConvertUntypedToString mode, untyped atomic values are always converted to strings: this corresponds to the XPath "eq" operator (and to the rules for xsl:key).
Each MultiIndex index is in fact a set of sub-indexes, one for each primitive type encountered. In an expression such as $seq[./A = $B], one sub-index is built for each primitive type that occurs in the sequence $B. In this index, any untyped atomic values in ./A are converted to that primitive type. For an expression such as $seq[./A eq $B], a single index is built, in which untyped atomic values in ./A are converted to strings.
A particular difficulty arises where $B (in the expression $seq[./A eq $B]) is untypedAtomic. In this situation an index is built in which any untypedAtomic values in ./A are indexed as strings. While building the index, we note all the primitive types that occur in ./A, and then we convert the search term $B to each of these types in turn before doing the index lookup. In practice, of course, it is very rare for the index to be heterogeneous.
This class was previously IndexedClosure, and inherited from MemoClosure, so that the contents of the sequence were built lazily. In most cases, however, an index will be built as soon as the variable is used, so there is no benefit in delaying matters. Making the class a Value in its own right means that the class can be used in both compiled and interpreted scenarios.
|Constructor and Description|
Create a MultiIndex
|Modifier and Type||Method and Description|
Retrieve items that match a given index value
public MultiIndex(GroundedValue indexedValue)
indexedValue- the sequence to be indexed
public SequenceIterator findItems(Expression use, SequenceIterator values, boolean convertUntypedToOther, boolean firstOnly, AtomicComparer comparer, XPathContext context) throws XPathException
use- the expression whose value is to be matched
values- the set of values to be found
convertUntypedToOther- true if untypedAtomic values are to be converted to the type of the other operand
firstOnly- true if only the first matching value is needed
comparer- AtomicComparer used to compare values for equality (encapsulates a collation if necessary)
context- the dynamic evaluation context
XPathException- if a failure occurs
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