Graph Indices

An IndexableGraph is a Graph that supports the indexing of its vertices and edges. An index is a data structure that allows for the fast retrieval of an element by a particular key/value pair. The IndexableGraph interface has the following methods:

public <T extends Element> Index<T> createIndex(String indexName, Class<T> indexClass, Index.Type type);
public <T extends Element> Index<T> getIndex(String indexName, Class<T> indexClass);
public Iterable<Index<? extends Element>> getIndices();
public void dropIndex(String indexName);

Manual Indices

There are two types of indices: Type.AUTOMATIC and Type.MANUAL. A manual index requires the developer to manually put, get, and remove elements from the index. To create a manual index of vertices, do the following:

Index<Vertex> index = graph.createIndex("test-idx", Vertex.class, Index.Type.MANUAL);

The Index interface has the following methods:

public String getIndexName();
public Class<T> getIndexClass();
public Type getIndexType();
public void put(String key, Object value, T element);
public Iterable<T> get(String key, Object value);
public void remove(String key, Object value, T element);

Given the index object created previous, to add, query, and remove a vertex from this index, do the following:

index.put("name","peter",vertex);
Iterable<Vertex> results = index.get("name","peter");
index.remove("name","peter",vertex);

With manual indices, the developer must be cognizant of maintaining the index with these methods.

Automatic Indices

When the developer does not wish to maintain an index, the developer can rely on indices of Type.AUTOMATIC. An automatic index will automatically put and remove elements from an index as the element mutates. That is, an automatic index indexes the properties of an element where the property key is the key and the property value is the value. As these properties change, an automatic index automatically reflects these changes. To create an automatic index, do the following:

Index<Vertex> autoIndex = graph.createIndex("test-aidx", Vertex.class, Type.AUTOMATIC);

The AutomaticIndex interface extends Index and provides, along with the Index methods, the following methods:

public void addAutoIndexKey(String key);
public void removeAutoIndexKey(String key);
public Set<String> getAutoIndexKeys();

An AutomaticIndex, when initially created will index all newly created vertices by all their properties. This is because getAutoIndexKeys() returns null, where null serves to denote wildcard. To restrict the index to be aware of only certain properties, use addAutoIndexKey(String key). Here is an example of all this together:

autoIndex.addAutoIndexKey("name");
Vertex a = graph.addVertex(null);
a.setProperty("name","pavel");
a.setProperty("country","belarus");
Iterable<Vertex> results = autoIndex.get("name","pavel");
// results contains vertex a
results = autoIndex.get("country","belarus");
// results does not contain vertex a

Note: When an IndexableGraph is created a new (not constructed, but when there is no historic persistence), it comes with two automatic indices named Index.VERTICES and Index.EDGES. These indices automatically index any created vertices and edges, respectively. If these indices are not desired, simply graph.dropIndex(Index.VERTICES) and graph.dropIndex(Index.EDGES) before adding elements.