shenker93 / clickhouse-scala Goto Github PK

import chdriver.{Client, ClickhouseProperties, Decoder}
import chdriver.columns.Column

// that's your domain class
case class Test(x: Int, y: Int)

// 'Decoder' is a typeclass that knows how to return a combinable `Iterator[Test]`, 
// those iterators will be concatenated and serve as a result of select query.
implicit val TestDecoder = new Decoder[Test] {
  override def validate(names: Array[String], types: Array[String]): Boolean = {
    names.sameElements(Array("x", "y")) &&
      types.sameElements(Array("Int32", "Int32"))
  }

  // it's a sample implementation, another one may be more performant with your constrains
  // see Decoder's sources for design explanations
  override def transpose(numberOfItems: Int, columns: Array[Column]): Iterator[Test] = {
    val xs = new Array[Int](numberOfItems)
    System.arraycopy(columns(0).data, 0, xs, 0, numberOfItems)
    val ys = new Array[Int](numberOfItems)
    System.arraycopy(columns(1).data, 0, ys, 0, numberOfItems)

    var i = 0
    new Iterator[Test] {
      override def hasNext = i < numberOfItems

      override def next() = {
        val res = Test(xs(i), ys(i))
        i += 1
        res
      }
    }
  }
}
    
val client = new Client()
val clickhouseProperties = new ClickhouseProperties()
val result = client.execute("select x, y from test limit 1000000", clickhouseProperties)(TestDecoder)
println(result.toList)