[英]Opening existing embedded neo4j database
我试图在嵌入式jave Neo4j api上使用scala。 我在打开数据库以便以后读取时遇到麻烦。 下面的代码应在每次运行时创建两个节点和一个边缘,但在每次运行开始时将其全部返回。 因此,第一次0节点,第二次2节点,第三次4等等。
import org.neo4j.tooling.GlobalGraphOperations
import org.neo4j.graphdb.factory.GraphDatabaseFactory
import org.neo4j.graphdb.RelationshipType
object tester extends App{
val DB_PATH = "data/neo4j"
object KNOWS extends RelationshipType {
override def name(): String = "KNOWS"
}
val graphDb = new GraphDatabaseFactory().newEmbeddedDatabase(DB_PATH) //seems to reset the whole directory
println(graphDb)
try {
println("Begin")
val tx = graphDb.beginTx() // Database operations go here
println(GlobalGraphOperations.at(graphDb).getAllNodes.iterator)
val nodes = GlobalGraphOperations.at(graphDb).getAllNodes.iterator
while (nodes.hasNext()) {
println(nodes.next())
}
nodes.close()
val relT = GlobalGraphOperations.at(graphDb).getAllRelationships.iterator
while (relT.hasNext()) {
println(relT.next())
}
println("Success - Begin")
tx.success()
}
try {
val tx = graphDb.beginTx() // Database operations go here
val firstNode = graphDb.createNode
val secondNode = graphDb.createNode
val relationship = firstNode.createRelationshipTo(secondNode, KNOWS)
println(firstNode)
println(secondNode)
println(relationship)
println(relationship.getType.name)
tx.success()
println("Success")
}
println("End")
try {
val tx = graphDb.beginTx() // Database operations go here
println(GlobalGraphOperations.at(graphDb).getAllNodes.iterator)
val nodes = GlobalGraphOperations.at(graphDb).getAllNodes.iterator
while (nodes.hasNext()) {
println(nodes.next())
}
nodes.close()
val relT = GlobalGraphOperations.at(graphDb).getAllRelationships.iterator
while (relT.hasNext()) {
println(relT.next())
}
println("Success - End")
tx.success()
}
graphDb.shutdown()
}
但是,每次似乎只是给一个空数据库,然后是两个新节点。 这里发生了什么?
EmbeddedGraphDatabase [data/neo4j]
Begin
org.neo4j.tooling.GlobalGraphOperations$1$1@74c49a90
Success - Begin
Node[2]
Node[3]
Relationship[1]
KNOWS
Success
End
org.neo4j.tooling.GlobalGraphOperations$1$1@2ec0df08
Node[2]
Node[3]
Relationship[1]
Success - End
Process finished with exit code 0
发生这种情况是因为您没有关闭事务 。 您可以通过调用tx.close()
。 我也认为在try
中实例化tx
并不完全应该如此。 这是程序的工作版本:
import org.neo4j.tooling.GlobalGraphOperations
import org.neo4j.graphdb.factory.GraphDatabaseFactory
import org.neo4j.graphdb.RelationshipType
object tester extends App{
val DB_PATH = "data/neo4j"
object KNOWS extends RelationshipType {
override def name(): String = "KNOWS"
}
val graphDb = new GraphDatabaseFactory().newEmbeddedDatabase(DB_PATH)
println(graphDb)
val tx1 = graphDb.beginTx() // Database operations go here
try {
println("Will list all nodes")
println("1 - Begin")
println("GlobalGraphOperations.at(graphDb).getAllNodes.iterator")
val nodes = GlobalGraphOperations.at(graphDb).getAllNodes.iterator
while (nodes.hasNext()) {
println(nodes.next())
}
nodes.close()
val relT = GlobalGraphOperations.at(graphDb).getAllRelationships.iterator
while (relT.hasNext()) {
println(relT.next())
}
println("1 - Success - Begin")
tx1.success()
}
finally {
tx1.close()
}
val tx2 = graphDb.beginTx() // Database operations go here
try {
val firstNode = graphDb.createNode
val secondNode = graphDb.createNode
val relationship = firstNode.createRelationshipTo(secondNode, KNOWS)
println(firstNode)
println(secondNode)
println(relationship)
println(relationship.getType.name)
tx2.success()
println("2 - Success")
}
finally {
tx2.close()
}
println("2 - End")
val tx3 = graphDb.beginTx() // Database operations go here
try {
println(GlobalGraphOperations.at(graphDb).getAllNodes.iterator)
val nodes = GlobalGraphOperations.at(graphDb).getAllNodes.iterator
while (nodes.hasNext()) {
println(nodes.next())
}
nodes.close()
val relT = GlobalGraphOperations.at(graphDb).getAllRelationships.iterator
while (relT.hasNext()) {
println(relT.next())
}
println("3 - Success - End")
tx3.success()
}
finally {
tx3.close()
}
graphDb.shutdown()
}
我试图使您的程序更接近“ scala风格”。 另外,我尝试删除样板并重复代码。 为此,我:
JavaConverters
来处理Java集合和Iterables,就像我们在Scala中处理它们一样 withTransaction
的方法来为我们在Scala中的交易获取自动资源管理 。 结果如下:
import org.neo4j.tooling.GlobalGraphOperations
import org.neo4j.graphdb.factory.GraphDatabaseFactory
import org.neo4j.graphdb.RelationshipType
import org.neo4j.graphdb.Transaction
import scala.collection.JavaConverters._
object tester extends App{
val DB_PATH = "data/neo4j"
object KNOWS extends RelationshipType {
override def name(): String = "KNOWS"
}
def withTransaction (doWithTransaction: Transaction => Unit) {
val tempTx = graphDb.beginTx()
try {
doWithTransaction(tempTx)
}
finally {
tempTx.close()
}
}
val graphDb = new GraphDatabaseFactory().newEmbeddedDatabase(DB_PATH)
println(graphDb)
withTransaction { tx =>
println("1 - Begin")
val nodes = GlobalGraphOperations.at(graphDb).getAllNodes
for (node <- nodes.asScala)
println(node)
val relTs = GlobalGraphOperations.at(graphDb).getAllRelationships
for (irelT <- relTs.asScala)
println(irelT)
println("1 - Success - Begin")
tx.success()
}
withTransaction { tx =>
val firstNode = graphDb.createNode
val secondNode = graphDb.createNode
val relationship = firstNode.createRelationshipTo(secondNode, KNOWS)
println(firstNode)
println(secondNode)
println(relationship)
println(relationship.getType.name)
tx.success()
println("2 - Success")
}
println("2 - End")
withTransaction { tx =>
println(GlobalGraphOperations.at(graphDb).getAllNodes.iterator)
val nodes = GlobalGraphOperations.at(graphDb).getAllNodes
for (node <- nodes.asScala)
println(node)
val relTs = GlobalGraphOperations.at(graphDb).getAllRelationships
for (irelT <- relTs.asScala)
println(irelT)
println("3 - Success - End")
tx.success()
}
graphDb.shutdown()
}
问题是您要指定相对路径。 可能是因为每次运行清理并构建时都清空目标目录(或dist,或任何其他想法,开发框架用作分发目录),所以数据库为空,因为它是从头开始创建的。 尝试使用绝对路径。
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