Question

我正在尝试在嵌入式jave Neo4j api上使用scala。我无法打开数据库以便随后阅读。下面的代码应该在每次运行时创建两个节点和一个边，但是在每次运行开始时返回所有节点。所以，0个节点第一次，2个节点第二次，4个第三次等。

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()
}

然而，每次它似乎只是给出一个空数据库，然后是2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

Answer 1

这种情况正在发生，因为你不是closing the transaction。您可以致电tx.close()来完成此操作。另外我认为在tx内实例化try并不完全是应该如何。这是您的程序的工作版本：

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()
}

EXTRA

我试图让你的程序更接近“scala-style”。此外，我试图删除样板和重复的代码。要做到这一点我：

使用JavaConverters处理Java集合和Iterables，就像我们在Scala中处理它们一样。
为scala中的事务创建了一个方法withTransaction以获取automatic resource management。

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()
}

Answer 2

问题是您正在指定相对路径。可能是每次你运行一个干净并建立你清空你的目标目录（或dist，或任何你的ide，开发框架用作分发目录）所以数据库是空的，因为它是从头开始每次创建。尝试使用绝对路径。

打开现有的嵌入式neo4j数据库

2 个答案:

EXTRA