使用Scala的Neo4j OGM示例

Question

我尝试了Luanne的文章The essence of Spring Data Neo4j 4 in Scala中提到的示例。代码可以在neo4j-ogm-scala存储库中找到。

package neo4j.ogm.scala.domain

import org.neo4j.ogm.annotation.GraphId;
import scala.beans.BeanProperty
import org.neo4j.ogm.annotation.NodeEntity
import org.neo4j.ogm.annotation.Relationship
import org.neo4j.ogm.session.Session;
import org.neo4j.ogm.session.SessionFactory;

abstract class Entity {
  @GraphId
  @BeanProperty
  var id: Long = _

  override def equals(o: Any): Boolean = o match {
    case other: Entity => other.id.equals(this.id)
    case _ => false
  }

  override def hashCode: Int = id.hashCode()
}

@NodeEntity
class Category extends Entity {
  var name: String = _

  def this(name: String) {
    this()
    this.name = name
  }
}

@NodeEntity
class Ingredient extends Entity {
  var name: String = _

  @Relationship(`type` = "HAS_CATEGORY", direction = "OUTGOING")
  var category: Category = _

  @Relationship(`type` = "PAIRS_WITH", direction = "UNDIRECTED")
  var pairings: Set[Pairing] = Set()

  def addPairing(pairing: Pairing): Unit = {
    pairing.first.pairings +(pairing)
    pairing.second.pairings +(pairing)
  }

  def this(name: String, category: Category) {
    this()
    this.name = name
    this.category = category
  }
}

@RelationshipEntity(`type` = "PAIRS_WITH")
class Pairing extends Entity {
  @StartNode
  var first: Ingredient = _

  @EndNode
  var second: Ingredient = _

  def this(first: Ingredient, second: Ingredient) {
    this()
    this.first = first
    this.second = second
  }
}

object Neo4jSessionFactory {
  val sessionFactory = new SessionFactory("neo4j.ogm.scala.domain")

  def getNeo4jSession(): Session = {
    System.setProperty("username", "neo4j")
    System.setProperty("password", "neo4j")
    sessionFactory.openSession("http://localhost:7474")
  }
}

object Main extends App {
  val spices = new Category("Spices")
  val turmeric = new Ingredient("Turmeric", spices)
  val cumin = new Ingredient("Cumin", spices)

  val pairing = new Pairing(turmeric, cumin)
  cumin.addPairing(pairing)

  val session = Neo4jSessionFactory.getNeo4jSession()
  val tx: Transaction = session.beginTransaction()

  try {
    session.save(spices)
    session.save(turmeric)
    session.save(cumin)
    session.save(pairing)
    tx.commit()
  } catch {
    case e: Exception => // tx.rollback()
  } finally {
//    tx.commit()
  }
}

问题是没有任何东西被保存到Neo4j中。你能指出我代码中的问题吗？

谢谢,

马诺杰。

Answer 1

Scala的Long是一个值类的实例。显式引入值类是为了避免分配运行时对象。因此，在JVM级别，Scala的Long等同于Java的原语long，这就是为什么它具有原语类型签名J的原因。因此，它不能为null，并且不应用作graphId。尽管Scala主要会在自己的Long和Java的Long类之间进行自动装箱，但这并不适用于声明，只适用于对这些对象的操作。

Answer 2

你的实体上没有接收到@GraphId。我对Scala一无所知，但是看起来scala long不太受OGM喜欢；var id: java.lang.Long = _运行得很好。