带有新的 firebase-server-sdk 的 Scala 案例类

Question

firebase firebase-server-sdk (3.0.1) 的新服务器 SDK 是否支持 Scala 案例类反序列化？以前的 firebase java sdk 使用了 jackson，您可以将其插入 scala module 以支持案例类。不清楚是否可以用新的 SDK 做类似的事情？它使用 Gson 还是一些自定义类映射器？

最简单的例子：

case class Person(firstName: String, lastName: String, age: Int)

使用 Firebase 侦听器设置，例如：

var options = new FirebaseOptions.Builder()
  .setDatabaseUrl("https://<your firebase>.firebaseio.com")
  .setServiceAccount(new FileInputStream("firebase-auth.json"))
  .build()

FirebaseApp.initializeApp(options);

var ref = FirebaseDatabase.getInstance().getReference("somepath")
ref.addListenerForSingleValueEvent(new ValueEventListener {
  override def onDataChange(dataSnapshot: DataSnapshot): Unit = {
    println(dataSnapshot.getValue(classOf[Person]))
  }

  override def onCancelled(databaseError: DatabaseError): Unit = {
    println(databaseError.getMessage)
  }
})

这将在 getValue 调用 dataSnapshot.getValue(classOf[Person]) 上失败，但以下情况除外：

Exception in thread "FirebaseDatabaseEventTarget" com.google.firebase.database.DatabaseException: No properties to serialize found on class Person
    at com.google.firebase.database.utilities.encoding.CustomClassMapper$BeanMapper.<init>(CustomClassMapper.java:495)
    at com.google.firebase.database.utilities.encoding.CustomClassMapper.loadOrCreateBeanMapperForClass(CustomClassMapper.java:285)
    at com.google.firebase.database.utilities.encoding.CustomClassMapper.convertBean(CustomClassMapper.java:379)
    at com.google.firebase.database.utilities.encoding.CustomClassMapper.deserializeToClass(CustomClassMapper.java:187)
    at com.google.firebase.database.utilities.encoding.CustomClassMapper.convertToCustomClass(CustomClassMapper.java:61)
    at com.google.firebase.database.DataSnapshot.getValue(DataSnapshot.java:181)
    at PetEventsNodeActorSpec$$anonfun$2$$anonfun$apply$mcV$sp$2$$anonfun$apply$mcV$sp$3$$anon$1.onDataChange(PetEventsNodeActorSpec.scala:290)
    at com.google.firebase.database.Query$1.onDataChange(Query.java:147)
    at com.google.firebase.database.core.ValueEventRegistration.fireEvent(ValueEventRegistration.java:57)
    at com.google.firebase.database.core.view.DataEvent.fire(DataEvent.java:45)
    at com.google.firebase.database.core.view.EventRaiser$1.run(EventRaiser.java:35)
    at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142)
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617)
    at java.lang.Thread.run(Thread.java:745)

我尝试向类添加注释，例如@BeanProperty，但随后得到：

Exception in thread "FirebaseDatabaseEventTarget" com.google.firebase.database.DatabaseException: Class Person is missing a constructor with no arguments

与其陷入为每个案例类添加注释或添加代码的兔子洞，还有什么想法可以让 scala 案例类与新的 firebase sdk 很好地配合使用？

Answer 1

AFAIK，没有办法直接使用案例类。我最终创建了带有@BeanProperty 注释的普通类，然后将它们转换为案例类。原因

Exception in thread "FirebaseDatabaseEventTarget" com.google.firebase.database.DatabaseException: Class Person is missing a constructor with no arguments

是因为你的类构造函数必须是空的（即它不能接受任何参数）：

import scala.beans.BeanProperty

case class Person(firstName: String, lastName: String, age: Int) {
  def toBean: PersonBean = {
    val person = new PersonBean()
    person.firstName = firstName
    person.lastName = lastName
    person.age = age
    person
  }
}

class PersonBean() {
  @BeanProperty var firstName: String = ""
  @BeanProperty var lastName: String = ""
  @BeanProperty var age: Int = 0
  def toCase: Person = Person(firstName, lastName, age)
}

var ref = FirebaseDatabase.getInstance().getReference("somepath")
ref.addListenerForSingleValueEvent(new ValueEventListener {
  override def onDataChange(dataSnapshot: DataSnapshot): Unit = {
    val record = dataSnapshot.getValue(classOf[PersonBean])
    val person = if (record != null) record.toCase else null
  }

  override def onCancelled(databaseError: DatabaseError): Unit = {
    println(databaseError.getMessage)
  }
})