Spark SQL: register a table using a case class that has user-defined types

SparkSQL-UDFTypes.scala

/**
 * We want to register a table with Spark SQL whose rows are composed of 2 longs and 1 String.
 * We would like to put restrictions of the shape of the String: for example, that it doesn't 
 * contain non-alphanumeric characters (or whatever...)
 * Let's define what we want:
*/

// CleanString defined somewhere else 
case class MyCaseClass(firstP: Long, secondP: Long, thirdP: CleanString)

// The obvious advantage of this signature is that it forces the strign to be as I want it to be, 
// otherwise the compiler screams. 

/**
 * OK. Let's now suppose that I end up with an RDD that holds the data I want on the table 
*/ 

val theSchemaRDD: RDD[MyCaseClass] = ... // compute the thing 
val sqlContext = new org.apache.spark.sql.SQLContext(sc)
import sqlContext._
theSchemaRDD.registerAsTable("accounts") // <- this fails with a scala.MatchError 

/**
 * So, *why* does it fail with a MatchError? I think it is because Catalyst tries to infer
 * the schema of the RDD, and it sees a type he does not know
 * (cf https://github.com/apache/spark/blob/05308426f0f51273be95fb1ca2cb1ec19d83cec8/sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/ScalaReflection.scala, 
 *  line 53+, or lookup function schemaFor)
 * 
 * How do we solve that??? 
 * We could try to make the constructor of the case class private, and force access 
 * through the companion object: 
*/ 
trait anAccount {
  val accountKey: Long
  val accountId: Long
  val accountName: String
}

object anAccount {
  def apply(accountKey: Long, accountId: Long, accountName: String): anAccount = {
    anAccountImpl(accountKey, accountId, CleanString(accountName).toString)
  }
  private case class anAccountImpl(accountKey: Long, accountId: Long, accountName: String) extends anAccount
}

// Unfortunately theSchemaRDD:: 
val theSchemaRDD: RDD[MyCaseClass] = ... // compute the thing
// is NOT an RDD of case class anymore, and then 
// can NOT be implicitly converted into a SchemaRDD, so I can not register it as a table 
// (references or exact code for this assertion to be found yet)
// The advantage here is that, at least, the compiler complains...