是否有办法使用Java API访问OrientDB中的边缘索引，以确定具有给定标签的边是否存在于两个已知顶点之间？
Afaik tinkergraph没有公开任何方法吗？
我相信Neo4j正在提供这样的API：
graphDatabaseService.index().forRelationships("HAS_USER").get(key, valueOrNull, startNodeOrNull, endNodeOrNull)
答案 0 :(得分：2)
您可以从顶点调用getEdges（）。例如：
v1.getEdges(v2, Direction.BOTH, "HAS_USER");
这是JavaDoc：
/**
* (Blueprints Extension) Returns all the edges from the current Vertex to another one.
*
* @param iDestination
* The target vertex
* @param iDirection
* The direction between OUT, IN or BOTH
* @param iLabels
* Optional labels as Strings to consider
* @return
*/
public Iterable<Edge> getEdges(final OrientVertex iDestination, final Direction iDirection, final String... iLabels)
答案 1 :(得分：1)
另一种方法是使用OrientGraph.getEdges()
首先通过以下方式创建索引非常重要：
cmd.setText("create index edge.HAS_ITEM on E (out,in) unique");
g.command(cmd).execute();
或通过纯Java：
OrientEdgeType e = g.getEdgeType("E");
e.createProperty("in", OType.LINK);
e.createProperty("out", OType.LINK);
e.createIndex("edge.has_item", OClass.INDEX_TYPE.UNIQUE_HASH_INDEX, "out", "in");
在此之后，可以使用以下方法查询索引：
Iterable<Edge> edges = g.getEdges("edge.has_item", new OCompositeKey(root.getId(), randomDocument.getId()));
小pittfall：在getEdges方法中引用它时，小写索引类型很重要。否则orientdb将无法检索它。
下面列出了一个完整的示例，其中显示了在两个顶点之间找到特定边的四种方法。
在示例中，创建了14k顶点（项），它们连接到单个根节点。
Creating {14000} items.
[graph.getEdges] Duration: 38
[graph.getEdges] Duration per lookup: 0.0095
[root.getEdges] Duration: 59439
[root.getEdges] Duration per lookup: 14.85975
[root.getEdges - iterating] Duration: 56710
[root.getEdges - iterating] Duration per lookup: 14.1775
[query] Duration: 817
[query] Duration per lookup: 0.20425
示例：
package de.jotschi.orientdb;
import static org.junit.Assert.assertTrue;
import java.util.ArrayList;
import java.util.List;
import org.junit.BeforeClass;
import org.junit.Test;
import com.orientechnologies.orient.core.index.OCompositeKey;
import com.orientechnologies.orient.core.metadata.schema.OType;
import com.orientechnologies.orient.core.sql.OCommandSQL;
import com.tinkerpop.blueprints.Direction;
import com.tinkerpop.blueprints.Edge;
import com.tinkerpop.blueprints.Vertex;
import com.tinkerpop.blueprints.impls.orient.OrientEdgeType;
import com.tinkerpop.blueprints.impls.orient.OrientGraphFactory;
import com.tinkerpop.blueprints.impls.orient.OrientGraphNoTx;
import com.tinkerpop.blueprints.impls.orient.OrientVertex;
import com.tinkerpop.blueprints.impls.orient.OrientVertexType;
public class EdgeIndexPerformanceTest {
private static OrientGraphFactory factory = new OrientGraphFactory("memory:tinkerpop");
private final static int nDocuments = 14000;
private final static int nChecks = 4000;
private static List<OrientVertex> items;
private static OrientVertex root;
@BeforeClass
public static void setupDatabase() {
setupTypesAndIndices(factory);
root = createRoot(factory);
items = createData(root, factory, nDocuments);
}
private static void setupTypesAndIndices(OrientGraphFactory factory2) {
OrientGraphNoTx g = factory.getNoTx();
try {
OCommandSQL cmd = new OCommandSQL();
cmd.setText("alter database custom useLightweightEdges=false");
g.command(cmd).execute();
cmd.setText("alter database custom useVertexFieldsForEdgeLabels=false");
g.command(cmd).execute();
OrientEdgeType e = g.getEdgeType("E");
e.createProperty("in", OType.LINK);
e.createProperty("out", OType.LINK);
OrientVertexType v = g.createVertexType("root", "V");
v.createProperty("name", OType.STRING);
v = g.createVertexType("item", "V");
v.createProperty("name", OType.STRING);
cmd.setText("create index edge.HAS_ITEM on E (out,in) unique");
g.command(cmd).execute();
} finally {
g.shutdown();
}
}
private static List<OrientVertex> createData(OrientVertex root, OrientGraphFactory factory, int count) {
OrientGraphNoTx g = factory.getNoTx();
try {
System.out.println("Creating {" + count + "} items.");
List<OrientVertex> items = new ArrayList<>();
for (int i = 0; i < count; i++) {
OrientVertex item = g.addVertex("class:item");
item.setProperty("name", "item_" + i);
items.add(item);
root.addEdge("HAS_ITEM", item, "class:E");
}
return items;
} finally {
g.shutdown();
}
}
private static OrientVertex createRoot(OrientGraphFactory factory) {
OrientGraphNoTx g = factory.getNoTx();
try {
OrientVertex root = g.addVertex("class:root");
root.setProperty("name", "root vertex");
return root;
} finally {
g.shutdown();
}
}
@Test
public void testEdgeIndexViaRootGetEdgesWithoutTarget() throws Exception {
OrientGraphNoTx g = factory.getNoTx();
try {
long start = System.currentTimeMillis();
for (int i = 0; i < nChecks; i++) {
OrientVertex randomDocument = items.get((int) (Math.random() * items.size()));
Iterable<Edge> edges = root.getEdges(Direction.OUT, "HAS_ITEM");
boolean found = false;
for (Edge edge : edges) {
if (edge.getVertex(Direction.IN).equals(randomDocument)) {
found = true;
break;
}
}
assertTrue(found);
}
long dur = System.currentTimeMillis() - start;
System.out.println("[root.getEdges - iterating] Duration: " + dur);
System.out.println("[root.getEdges - iterating] Duration per lookup: " + ((double) dur / (double) nChecks));
} finally {
g.shutdown();
}
}
@Test
public void testEdgeIndexViaRootGetEdges() throws Exception {
OrientGraphNoTx g = factory.getNoTx();
try {
long start = System.currentTimeMillis();
for (int i = 0; i < nChecks; i++) {
OrientVertex randomDocument = items.get((int) (Math.random() * items.size()));
Iterable<Edge> edges = root.getEdges(randomDocument, Direction.OUT, "HAS_ITEM");
assertTrue(edges.iterator().hasNext());
}
long dur = System.currentTimeMillis() - start;
System.out.println("[root.getEdges] Duration: " + dur);
System.out.println("[root.getEdges] Duration per lookup: " + ((double) dur / (double) nChecks));
} finally {
g.shutdown();
}
}
@Test
public void testEdgeIndexViaGraphGetEdges() throws Exception {
OrientGraphNoTx g = factory.getNoTx();
try {
long start = System.currentTimeMillis();
for (int i = 0; i < nChecks; i++) {
OrientVertex randomDocument = items.get((int) (Math.random() * items.size()));
Iterable<Edge> edges = g.getEdges("edge.has_item", new OCompositeKey(root.getId(), randomDocument.getId()));
assertTrue(edges.iterator().hasNext());
}
long dur = System.currentTimeMillis() - start;
System.out.println("[graph.getEdges] Duration: " + dur);
System.out.println("[graph.getEdges] Duration per lookup: " + ((double) dur / (double) nChecks));
} finally {
g.shutdown();
}
}
@Test
public void testEdgeIndexViaQuery() throws Exception {
OrientGraphNoTx g = factory.getNoTx();
try {
System.out.println("Checking edge");
long start = System.currentTimeMillis();
for (int i = 0; i < nChecks; i++) {
OrientVertex randomDocument = items.get((int) (Math.random() * items.size()));
OCommandSQL cmd = new OCommandSQL("select from index:edge.has_item where key=?");
OCompositeKey key = new OCompositeKey(root.getId(), randomDocument.getId());
assertTrue(((Iterable<Vertex>) g.command(cmd).execute(key)).iterator().hasNext());
}
long dur = System.currentTimeMillis() - start;
System.out.println("[query] Duration: " + dur);
System.out.println("[query] Duration per lookup: " + ((double) dur / (double) nChecks));
} finally {
g.shutdown();
}
}
}