我正在尝试使用ScalaPB从Avro4s生成的案例类（来自Protobuf定义）派生Avro Schema，但无法成功。下面的示例显示了问题。
我的protobuf文件test.proto：
message Test {
// Unix timestamp in milliseconds
required int64 time_ms = 1;
// user_id
optional string UUID = 2;
}
我使用ScalaPB生成Test案例类：
// Generated by the Scala Plugin for the Protocol Buffer Compiler.
// Do not edit!
//
// Protofile syntax: PROTO2
package test
/** @param timeMs
* Unix timestamp in milliseconds
* @param uUID
* user_id
*/
@SerialVersionUID(0L)
final case class Test(
timeMs: _root_.scala.Long,
uUID: _root_.scala.Option[_root_.scala.Predef.String] = None
) extends scalapb.GeneratedMessage with scalapb.Message[Test] with scalapb.lenses.Updatable[Test] {
@transient
private[this] var __serializedSizeCachedValue: _root_.scala.Int = 0
private[this] def __computeSerializedValue(): _root_.scala.Int = {
var __size = 0
{
val __value = timeMs
__size += _root_.com.google.protobuf.CodedOutputStream.computeInt64Size(1, __value)
};
if (uUID.isDefined) {
val __value = uUID.get
__size += _root_.com.google.protobuf.CodedOutputStream.computeStringSize(2, __value)
};
__size
}
final override def serializedSize: _root_.scala.Int = {
var read = __serializedSizeCachedValue
if (read == 0) {
read = __computeSerializedValue()
__serializedSizeCachedValue = read
}
read
}
def writeTo(`_output__`: _root_.com.google.protobuf.CodedOutputStream): _root_.scala.Unit = {
{
val __v = timeMs
_output__.writeInt64(1, __v)
};
uUID.foreach { __v =>
val __m = __v
_output__.writeString(2, __m)
};
}
def mergeFrom(`_input__`: _root_.com.google.protobuf.CodedInputStream): test.Test = {
var __timeMs = this.timeMs
var __uUID = this.uUID
var __requiredFields0: _root_.scala.Long = 0x1L
var _done__ = false
while (!_done__) {
val _tag__ = _input__.readTag()
_tag__ match {
case 0 => _done__ = true
case 8 =>
__timeMs = _input__.readInt64()
__requiredFields0 &= 0xfffffffffffffffeL
case 18 =>
__uUID = Option(_input__.readString())
case tag => _input__.skipField(tag)
}
}
if (__requiredFields0 != 0L) { throw new _root_.com.google.protobuf.InvalidProtocolBufferException("Message missing required fields.") }
test.Test(
timeMs = __timeMs,
uUID = __uUID
)
}
def withTimeMs(__v: _root_.scala.Long): Test = copy(timeMs = __v)
def getUUID: _root_.scala.Predef.String = uUID.getOrElse("")
def clearUUID: Test = copy(uUID = None)
def withUUID(__v: _root_.scala.Predef.String): Test = copy(uUID = Option(__v))
def getFieldByNumber(__fieldNumber: _root_.scala.Int): _root_.scala.Any = {
(__fieldNumber: @_root_.scala.unchecked) match {
case 1 => timeMs
case 2 => uUID.orNull
}
}
def getField(__field: _root_.scalapb.descriptors.FieldDescriptor): _root_.scalapb.descriptors.PValue = {
_root_.scala.Predef.require(__field.containingMessage eq companion.scalaDescriptor)
(__field.number: @_root_.scala.unchecked) match {
case 1 => _root_.scalapb.descriptors.PLong(timeMs)
case 2 => uUID.map(_root_.scalapb.descriptors.PString).getOrElse(_root_.scalapb.descriptors.PEmpty)
}
}
def toProtoString: _root_.scala.Predef.String = _root_.scalapb.TextFormat.printToUnicodeString(this)
def companion = test.Test
}
object Test extends scalapb.GeneratedMessageCompanion[test.Test] {
implicit def messageCompanion: scalapb.GeneratedMessageCompanion[test.Test] = this
def fromFieldsMap(__fieldsMap: scala.collection.immutable.Map[_root_.com.google.protobuf.Descriptors.FieldDescriptor, _root_.scala.Any]): test.Test = {
_root_.scala.Predef.require(__fieldsMap.keys.forall(_.getContainingType() == javaDescriptor), "FieldDescriptor does not match message type.")
val __fields = javaDescriptor.getFields
test.Test(
__fieldsMap(__fields.get(0)).asInstanceOf[_root_.scala.Long],
__fieldsMap.get(__fields.get(1)).asInstanceOf[_root_.scala.Option[_root_.scala.Predef.String]]
)
}
implicit def messageReads: _root_.scalapb.descriptors.Reads[test.Test] = _root_.scalapb.descriptors.Reads{
case _root_.scalapb.descriptors.PMessage(__fieldsMap) =>
_root_.scala.Predef.require(__fieldsMap.keys.forall(_.containingMessage == scalaDescriptor), "FieldDescriptor does not match message type.")
test.Test(
__fieldsMap.get(scalaDescriptor.findFieldByNumber(1).get).get.as[_root_.scala.Long],
__fieldsMap.get(scalaDescriptor.findFieldByNumber(2).get).flatMap(_.as[_root_.scala.Option[_root_.scala.Predef.String]])
)
case _ => throw new RuntimeException("Expected PMessage")
}
def javaDescriptor: _root_.com.google.protobuf.Descriptors.Descriptor = TestProto.javaDescriptor.getMessageTypes.get(0)
def scalaDescriptor: _root_.scalapb.descriptors.Descriptor = TestProto.scalaDescriptor.messages(0)
def messageCompanionForFieldNumber(__number: _root_.scala.Int): _root_.scalapb.GeneratedMessageCompanion[_] = throw new MatchError(__number)
lazy val nestedMessagesCompanions: Seq[_root_.scalapb.GeneratedMessageCompanion[_]] = Seq.empty
def enumCompanionForFieldNumber(__fieldNumber: _root_.scala.Int): _root_.scalapb.GeneratedEnumCompanion[_] = throw new MatchError(__fieldNumber)
lazy val defaultInstance = test.Test(
timeMs = 0L
)
implicit class TestLens[UpperPB](_l: _root_.scalapb.lenses.Lens[UpperPB, test.Test]) extends _root_.scalapb.lenses.ObjectLens[UpperPB, test.Test](_l) {
def timeMs: _root_.scalapb.lenses.Lens[UpperPB, _root_.scala.Long] = field(_.timeMs)((c_, f_) => c_.copy(timeMs = f_))
def uUID: _root_.scalapb.lenses.Lens[UpperPB, _root_.scala.Predef.String] = field(_.getUUID)((c_, f_) => c_.copy(uUID = Option(f_)))
def optionalUUID: _root_.scalapb.lenses.Lens[UpperPB, _root_.scala.Option[_root_.scala.Predef.String]] = field(_.uUID)((c_, f_) => c_.copy(uUID = f_))
}
final val TIME_MS_FIELD_NUMBER = 1
final val UUID_FIELD_NUMBER = 2
}
然后尝试如下导出Avro模式：
val schema = AvroSchema[Test]
我收到以下错误：
could not find implicit value for parameter schemaFor: com.sksamuel.avro4s.SchemaFor[test.Test]
我如何在这里成功？还有其他实用程序可以实现相同目的吗？
答案 0 :(得分：0)
ScalaPB的生成类包含许多基于PB运行时库的样板。在Avro中转换/读取protobuf消息的最安全方法之一是使用AvroProtobuf兼容性。您可以在org.apache.avro.protobuf软件包中找到有关它的更多信息。
您可以使用ProtobufData获取架构或执行SerDe操作。
答案 1 :(得分：0)
ScalaPB向生成的案例类添加@SerialVersionUID批注。由于https://github.com/sksamuel/avro4s/issues/300
答案 2 :(得分：0)
avro4s具有bug，当类具有Java注释时会导致错误。 ScalaPB添加了这样的注释-@SerialVersionUID。该问题已在最新的avro4s快照（3.0.0.X快照）中修复，并将在最终的3.0.0版本中发布。