Package com.googlecode.cqengine.metadata

Class MetadataEngine<O>

java.lang.Object

com.googlecode.cqengine.metadata.MetadataEngine<O>

public class MetadataEngine<O>
extends Object

Provides access to metadata for attributes, obtained from indexes which have been added to the collection. Example metadata:

• frequency distributions (counts of the occurrences of each distinct value of an attribute in the collection)
• count the number of objects in the collection whose attribute has a specific value
• obtain all of the distinct values of an attribute

The getAttributeMetadata(Attribute) method returns an AttributeMetadata accessor object, which can provide access to basic metadata as discussed above for a given attribute, in unsorted order. This requires in advance, an index which implements the KeyStatisticsAttributeIndex interface, to be added to the collection on the given attribute. Most indexes implement that interface.

The getSortedAttributeMetadata(Attribute) method returns a SortedAttributeMetadata accessor object, which can provide access to additional metadata and in sorted order. It allows attribute values to be traversed in ascending or descending order, and it supports range queries. This requires in advance, an index which implements the SortedKeyStatisticsAttributeIndex interface, to be added to the collection on the given attribute. That interface is implemented by many indexes.

This object can be accessed by calling IndexedCollection.getMetadataEngine().

Constructor Summary

Constructors

Constructor	Description
MetadataEngine(IndexedCollection<O> indexedCollection, Supplier<QueryOptions> openResourcesHandler, Consumer<QueryOptions> closeResourcesHandler)

Method Summary

Modifier and Type	Method	Description
<A> AttributeMetadata<A,O>	getAttributeMetadata(Attribute<O,A> attribute)	Returns an AttributeMetadata accessor object, which can provide access to basic metadata for a given attribute, in unsorted order.
<A extends Comparable<A>> SortedAttributeMetadata<A,O>	getSortedAttributeMetadata(Attribute<O,A> attribute)	Returns a SortedAttributeMetadata accessor object, which can provide access to metadata in sorted order for a given attribute.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Detail

MetadataEngine

public MetadataEngine(IndexedCollection<O> indexedCollection,
                      Supplier<QueryOptions> openResourcesHandler,
                      Consumer<QueryOptions> closeResourcesHandler)

Method Detail

getAttributeMetadata

public <A> AttributeMetadata<A,O> getAttributeMetadata(Attribute<O,A> attribute)

Returns an AttributeMetadata accessor object, which can provide access to basic metadata for a given attribute, in unsorted order.

This requires in advance, an index which implements the KeyStatisticsAttributeIndex interface, to be added to the collection on the given attribute.

Parameters:

attribute - The attribute for which metadata is required

Returns:

an AttributeMetadata accessor object

Throws:

IllegalStateException - if no suitable index has been added to the collection

getSortedAttributeMetadata

public <A extends Comparable<A>> SortedAttributeMetadata<A,O> getSortedAttributeMetadata(Attribute<O,A> attribute)

Returns a SortedAttributeMetadata accessor object, which can provide access to metadata in sorted order for a given attribute. It allows attribute values to be traversed in ascending or descending order, and it supports range queries.

This requires in advance, an index which implements the SortedKeyStatisticsAttributeIndex interface, to be added to the collection on the given attribute.

Parameters:

attribute - The attribute for which metadata is required

Returns:

an AttributeMetadata accessor object

Throws:

IllegalStateException - if no suitable index has been added to the collection