Cassandra 表中的 Blob 映射

Question

Trying to create new table, where each row can have extra data called context, which is key/value map. Key is string and value can be few bytes (bytes array).

The following definition doesn't compile, with the following error:

Error:(55, 30) Cannot find primitive implementation for class Array
  object context extends MapColumn[String, Array[Byte]] 

Here is my code:

case class UserJourny(
                       id: Long,
                       time: Int,
                       activity_type: Int,
                       context: Map[String, Array[Byte]]
               )


abstract class UserJournyModel extends Table[UserJournyModel, UserJourny] {
  override def tableName: String = "user_journy"

  object dyid extends BigIntColumn with PartitionKey {
    override lazy val name = "id"
  }

  object time extends IntColumn with ClusteringOrder with Descending {
    override lazy val name = "time"
  }

  object activity_type extends IntColumn
  object context extends MapColumn[String, Array[Byte]]
}

How should I do it right?

Answer 1

Use MapColumn[String, ByteBuffer] instead, which Cassandra natively understands. Then you need some basic fun stuff to encode a byte array to a buffer.

val buf = ByteBuffer.wrap(Array[Byte](1, 2, 3, 4, 5))

You can also derive a primitive to make your life easier overall.

implicit val byteArrayPrimitive = Primitive.derive[
  Array[Byte],
  ByteBuffer
](ByteBuffer.wrap)(_.array)

Now you can successfully use MapColumn[String, Array[Byte]] , and Cassandra will store it as a buffer anyway, it will have map<text, buffer> type inside.