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Posted to issues@spark.apache.org by "Cheng Lian (JIRA)" <ji...@apache.org> on 2015/03/29 12:32:52 UTC
[jira] [Comment Edited] (SPARK-6587) Inferring schema for case
class hierarchy fails with mysterious message
[ https://issues.apache.org/jira/browse/SPARK-6587?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14385695#comment-14385695 ]
Cheng Lian edited comment on SPARK-6587 at 3/29/15 10:32 AM:
-------------------------------------------------------------
This behavior is expected. There are two problems in your case:
# Because {{things}} contains instances of all three case classes, the type of {{things}} is {{Seq[MyHolder]}}. Since {{MyHolder}} doesn't extend {{Product}}, can't be recognized by {{ScalaReflection}}.
# You can only use a single concrete case class {{T}} when converting {{RDD[T]}} or {{Seq[T]}} to a DataFrame. For {{things}}, we can't figure out what data type should the {{foo}} field in the reflected schema have.
was (Author: lian cheng):
This behavior is expected. There are two problems in your case:
# Because {{things}} contains instances of all three case classes, the type of {{things}} is {{Seq[MyHolder]}}. Since {{MyHolder}} doesn't extend {{Product}}, can't be recognized by {{ScalaReflection}}.
# You can only use a single concrete case class {{T}} when converting {{RDD[T]}} or {{Seq[T]}} to a DataFrame. For {{things}}, we can't figure out what data type should the {{foo}} field in the reflected schema have.
> Inferring schema for case class hierarchy fails with mysterious message
> -----------------------------------------------------------------------
>
> Key: SPARK-6587
> URL: https://issues.apache.org/jira/browse/SPARK-6587
> Project: Spark
> Issue Type: Bug
> Components: SQL
> Affects Versions: 1.3.0
> Environment: At least Windows 8, Scala 2.11.2.
> Reporter: Spiro Michaylov
>
> (Don't know if this is a functionality bug, error reporting bug or an RFE ...)
> I define the following hierarchy:
> {code}
> private abstract class MyHolder
> private case class StringHolder(s: String) extends MyHolder
> private case class IntHolder(i: Int) extends MyHolder
> private case class BooleanHolder(b: Boolean) extends MyHolder
> {code}
> and a top level case class:
> {code}
> private case class Thing(key: Integer, foo: MyHolder)
> {code}
> When I try to convert it:
> {code}
> val things = Seq(
> Thing(1, IntHolder(42)),
> Thing(2, StringHolder("hello")),
> Thing(3, BooleanHolder(false))
> )
> val thingsDF = sc.parallelize(things, 4).toDF()
> thingsDF.registerTempTable("things")
> val all = sqlContext.sql("SELECT * from things")
> {code}
> I get the following stack trace:
> {noformat}
> Exception in thread "main" scala.MatchError: sql.CaseClassSchemaProblem.MyHolder (of class scala.reflect.internal.Types$ClassNoArgsTypeRef)
> at org.apache.spark.sql.catalyst.ScalaReflection$class.schemaFor(ScalaReflection.scala:112)
> at org.apache.spark.sql.catalyst.ScalaReflection$.schemaFor(ScalaReflection.scala:30)
> at org.apache.spark.sql.catalyst.ScalaReflection$$anonfun$schemaFor$1.apply(ScalaReflection.scala:159)
> at org.apache.spark.sql.catalyst.ScalaReflection$$anonfun$schemaFor$1.apply(ScalaReflection.scala:157)
> at scala.collection.immutable.List.map(List.scala:276)
> at org.apache.spark.sql.catalyst.ScalaReflection$class.schemaFor(ScalaReflection.scala:157)
> at org.apache.spark.sql.catalyst.ScalaReflection$.schemaFor(ScalaReflection.scala:30)
> at org.apache.spark.sql.catalyst.ScalaReflection$class.schemaFor(ScalaReflection.scala:107)
> at org.apache.spark.sql.catalyst.ScalaReflection$.schemaFor(ScalaReflection.scala:30)
> at org.apache.spark.sql.SQLContext.createDataFrame(SQLContext.scala:312)
> at org.apache.spark.sql.SQLContext$implicits$.rddToDataFrameHolder(SQLContext.scala:250)
> at sql.CaseClassSchemaProblem$.main(CaseClassSchemaProblem.scala:35)
> at sql.CaseClassSchemaProblem.main(CaseClassSchemaProblem.scala)
> at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
> at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57)
> at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
> at java.lang.reflect.Method.invoke(Method.java:606)
> at com.intellij.rt.execution.application.AppMain.main(AppMain.java:134)
> {noformat}
> I wrote this to answer [a question on StackOverflow|http://stackoverflow.com/questions/29310405/what-is-the-right-way-to-represent-an-any-type-in-spark-sql] which uses a much simpler approach and suffers the same problem.
> Looking at what seems to me to be the [relevant unit test suite|https://github.com/apache/spark/blob/master/sql/core/src/test/scala/org/apache/spark/sql/ScalaReflectionRelationSuite.scala] I see that this case is not covered.
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