打開現有的嵌入式neo4j數據庫

Question

我試圖在嵌入式jave Neo4j api上使用scala。 我在打開數據庫以便以后讀取時遇到麻煩。 下面的代碼應在每次運行時創建兩個節點和一個邊緣，但在每次運行開始時將其全部返回。 因此，第一次0節點，第二次2節點，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，每次似乎只是給一個空數據庫，然后是兩個新節點。 這里發生了什么？

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

發生這種情況是因為您沒有關閉事務 。 您可以通過調用tx.close() 。 我也認為在try中實例化tx並不完全應該如此。 這是程序的工作版本：

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()
}

額外

我試圖使您的程序更接近“ scala風格”。 另外，我嘗試刪除樣板並重復代碼。 為此，我：

• 使用JavaConverters來處理Java集合和Iterables，就像我們在Scala中處理它們一樣
• 創建了一個withTransaction的方法來為我們在Scala中的交易獲取自動資源管理 。

結果如下：

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

問題是您要指定相對路徑。 可能是因為每次運行清理並構建時都清空目標目錄（或dist，或任何其他想法，開發框架用作分發目錄），所以數據庫為空，因為它是從頭開始創建的。 嘗試使用絕對路徑。