The Path to Generic Endpoints using Shapeless

 
Scala eXchange, December 2017
Maria Livia Chiorean
 

Me

@MariaLiviaCh

The Guardian

Content API

Composer

Atom Tools

Content Atoms

  • Structured data
  • Reusable content with its own lifecycle
  • Simultaneous updates

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Atom Workshop

  • Currently we have > 10 types of atoms
  • Common components
  • Shared services
  • Built on Scala, Play and React

Generic API Endpoint

PATCH /api/:atomType/:id/:path
val atomData = MediaAtom(
     url = "gu.com",
     metadata = Some(Metadata( 
       commentsEnabled = Some(true), 
       channelId = Some("happy-friday"))))

val atomData = MediaAtom(
     title = "Tech time video",
     metadata = Some(Metadata( 
       commentsEnabled = Some(true), 
       channelId = Some("Scala"))))
/api/media/some-id/metadata.channelId
body: "Scala"

Atom Workshop Architecture

Thrift models

Backend

Frontend

JSON

Thrift + Scrooge

namespace * contentatom.qanda
namespace java com.gu.contentatom.thrift.atom.qanda
#@namespace scala com.gu.contentatom.thrift.atom.qanda

include "../shared.thrift"
include "storyquestions.thrift"

struct QAndAItem {
  1: optional string title
  2: required string body
}

struct QAndAAtom {
  1: optional string typeLabel
  3: optional shared.Image eventImage
  4: required QAndAItem item
  5: optional storyquestions.Question question
}
/**
 * Generated by Scrooge
 *   version: 4.16.0
 *   rev: 0201cac9fdd6188248d42da91fd14c87744cc4a5
 *   built at: 20170421-124523
 */
package com.gu.contentatom.thrift.atom.qanda

import com.twitter.scrooge.{
  HasThriftStructCodec3,
  LazyTProtocol,
  TFieldBlob,
  ThriftException,
  ThriftStruct,
  ThriftStructCodec3,
  ThriftStructFieldInfo,
  ThriftStructMetaData,
  ThriftUtil
}
import org.apache.thrift.protocol._
import org.apache.thrift.transport.{TMemoryBuffer, TTransport}
import java.nio.ByteBuffer
import java.util.Arrays
import scala.collection.immutable.{Map => immutable$Map}
import scala.collection.mutable.Builder
import scala.collection.mutable.{
  ArrayBuffer => mutable$ArrayBuffer, Buffer => mutable$Buffer,
  HashMap => mutable$HashMap, HashSet => mutable$HashSet}
import scala.collection.{Map, Set}


object QAndAAtom extends ThriftStructCodec3[QAndAAtom] {
  private val NoPassthroughFields = immutable$Map.empty[Short, TFieldBlob]
  val Struct = new TStruct("QAndAAtom")
  val TypeLabelField = new TField("typeLabel", TType.STRING, 1)
  val TypeLabelFieldManifest = implicitly[Manifest[String]]
  val EventImageField = new TField("eventImage", TType.STRUCT, 3)
  val EventImageFieldManifest = implicitly[Manifest[com.gu.contentatom.thrift.Image]]
  val ItemField = new TField("item", TType.STRUCT, 4)
  val ItemFieldManifest = implicitly[Manifest[com.gu.contentatom.thrift.atom.qanda.QAndAItem]]
  val QuestionField = new TField("question", TType.STRUCT, 5)
  val QuestionFieldManifest = implicitly[Manifest[com.gu.contentatom.thrift.atom.storyquestions.Question]]

  /**
   * Field information in declaration order.
   */
  lazy val fieldInfos: scala.List[ThriftStructFieldInfo] = scala.List[ThriftStructFieldInfo](
    new ThriftStructFieldInfo(
      TypeLabelField,
      true,
      false,
      TypeLabelFieldManifest,
      _root_.scala.None,
      _root_.scala.None,
      immutable$Map.empty[String, String],
      immutable$Map.empty[String, String],
      None
    ),
    new ThriftStructFieldInfo(
      EventImageField,
      true,
      false,
      EventImageFieldManifest,
      _root_.scala.None,
      _root_.scala.None,
      immutable$Map.empty[String, String],
      immutable$Map.empty[String, String],
      None
    ),
    new ThriftStructFieldInfo(
      ItemField,
      false,
      true,
      ItemFieldManifest,
      _root_.scala.None,
      _root_.scala.None,
      immutable$Map.empty[String, String],
      immutable$Map.empty[String, String],
      None
    ),
    new ThriftStructFieldInfo(
      QuestionField,
      true,
      false,
      QuestionFieldManifest,
      _root_.scala.None,
      _root_.scala.None,
      immutable$Map.empty[String, String],
      immutable$Map.empty[String, String],
      None
    )
  )

  lazy val structAnnotations: immutable$Map[String, String] =
    immutable$Map.empty[String, String]

  /**
   * Checks that all required fields are non-null.
   */
  def validate(_item: QAndAAtom): Unit = {
    if (_item.item == null) throw new TProtocolException("Required field item cannot be null")
  }

  def withoutPassthroughFields(original: QAndAAtom): QAndAAtom =
    new Immutable(
      typeLabel =
        {
          val field = original.typeLabel
          field.map { field =>
            field
          }
        },
      eventImage =
        {
          val field = original.eventImage
          field.map { field =>
            com.gu.contentatom.thrift.Image.withoutPassthroughFields(field)
          }
        },
      item =
        {
          val field = original.item
          com.gu.contentatom.thrift.atom.qanda.QAndAItem.withoutPassthroughFields(field)
        },
      question =
        {
          val field = original.question
          field.map { field =>
            com.gu.contentatom.thrift.atom.storyquestions.Question.withoutPassthroughFields(field)
          }
        }
    )

  override def encode(_item: QAndAAtom, _oproto: TProtocol): Unit = {
    _item.write(_oproto)
  }

  private[this] def lazyDecode(_iprot: LazyTProtocol): QAndAAtom = {

    var typeLabelOffset: Int = -1
    var eventImage: Option[com.gu.contentatom.thrift.Image] = None
    var item: com.gu.contentatom.thrift.atom.qanda.QAndAItem = null
    var _got_item = false
    var question: Option[com.gu.contentatom.thrift.atom.storyquestions.Question] = None

    var _passthroughFields: Builder[(Short, TFieldBlob), immutable$Map[Short, TFieldBlob]] = null
    var _done = false
    val _start_offset = _iprot.offset

    _iprot.readStructBegin()
    while (!_done) {
      val _field = _iprot.readFieldBegin()
      if (_field.`type` == TType.STOP) {
        _done = true
      } else {
        _field.id match {
          case 1 =>
            _field.`type` match {
              case TType.STRING =>
                typeLabelOffset = _iprot.offsetSkipString
    
              case _actualType =>
                val _expectedType = TType.STRING
                throw new TProtocolException(
                  "Received wrong type for field 'typeLabel' (expected=%s, actual=%s).".format(
                    ttypeToString(_expectedType),
                    ttypeToString(_actualType)
                  )
                )
            }
          case 3 =>
            _field.`type` match {
              case TType.STRUCT =>
    
                eventImage = Some(readEventImageValue(_iprot))
              case _actualType =>
                val _expectedType = TType.STRUCT
                throw new TProtocolException(
                  "Received wrong type for field 'eventImage' (expected=%s, actual=%s).".format(
                    ttypeToString(_expectedType),
                    ttypeToString(_actualType)
                  )
                )
            }
          case 4 =>
            _field.`type` match {
              case TType.STRUCT =>
    
                item = readItemValue(_iprot)
                _got_item = true
              case _actualType =>
                val _expectedType = TType.STRUCT
                throw new TProtocolException(
                  "Received wrong type for field 'item' (expected=%s, actual=%s).".format(
                    ttypeToString(_expectedType),
                    ttypeToString(_actualType)
                  )
                )
            }
          case 5 =>
            _field.`type` match {
              case TType.STRUCT =>
    
                question = Some(readQuestionValue(_iprot))
              case _actualType =>
                val _expectedType = TType.STRUCT
                throw new TProtocolException(
                  "Received wrong type for field 'question' (expected=%s, actual=%s).".format(
                    ttypeToString(_expectedType),
                    ttypeToString(_actualType)
                  )
                )
            }
          case _ =>
            if (_passthroughFields == null)
              _passthroughFields = immutable$Map.newBuilder[Short, TFieldBlob]
            _passthroughFields += (_field.id -> TFieldBlob.read(_field, _iprot))
        }
        _iprot.readFieldEnd()
      }
    }
    _iprot.readStructEnd()

    if (!_got_item) throw new TProtocolException("Required field 'item' was not found in serialized data for struct QAndAAtom")
    new LazyImmutable(
      _iprot,
      _iprot.buffer,
      _start_offset,
      _iprot.offset,
      typeLabelOffset,
      eventImage,
      item,
      question,
      if (_passthroughFields == null)
        NoPassthroughFields
      else
        _passthroughFields.result()
    )
  }
trait QAndAAtom
  extends ThriftStruct
  with _root_.scala.Product4[Option[String], Option[com.gu.contentatom.thrift.Image], com.gu.contentatom.thrift.atom.qanda.QAndAItem, Option[com.gu.contentatom.thrift.atom.storyquestions.Question]]
  with HasThriftStructCodec3[QAndAAtom]
  with java.io.Serializable
{
  import QAndAAtom._

  def typeLabel: _root_.scala.Option[String]
  def eventImage: _root_.scala.Option[com.gu.contentatom.thrift.Image]
  def item: com.gu.contentatom.thrift.atom.qanda.QAndAItem
  def question: _root_.scala.Option[com.gu.contentatom.thrift.atom.storyquestions.Question]

  def _passthroughFields: immutable$Map[Short, TFieldBlob] = immutable$Map.empty

  def _1 = typeLabel
  def _2 = eventImage
  def _3 = item
  def _4 = question

  def toTuple: _root_.scala.Tuple4[Option[String], Option[com.gu.contentatom.thrift.Image], com.gu.contentatom.thrift.atom.qanda.QAndAItem, Option[com.gu.contentatom.thrift.atom.storyquestions.Question]] = {
    (
      typeLabel,
      eventImage,
      item,
      question
    )
  }


  /**
   * Gets a field value encoded as a binary blob using TCompactProtocol.  If the specified field
   * is present in the passthrough map, that value is returned.  Otherwise, if the specified field
   * is known and not optional and set to None, then the field is serialized and returned.
   */
  def getFieldBlob(_fieldId: Short): _root_.scala.Option[TFieldBlob] = {
    lazy val _buff = new TMemoryBuffer(32)
    lazy val _oprot = new TCompactProtocol(_buff)
    _passthroughFields.get(_fieldId) match {
      case blob: _root_.scala.Some[TFieldBlob] => blob
      case _root_.scala.None => {
        val _fieldOpt: _root_.scala.Option[TField] =
          _fieldId match {
            case 1 =>
              if (typeLabel.isDefined) {
                writeTypeLabelValue(typeLabel.get, _oprot)
                _root_.scala.Some(QAndAAtom.TypeLabelField)
              } else {
                _root_.scala.None
              }
            case 3 =>
              if (eventImage.isDefined) {
                writeEventImageValue(eventImage.get, _oprot)
                _root_.scala.Some(QAndAAtom.EventImageField)
              } else {
                _root_.scala.None
              }
            case 4 =>
              if (item ne null) {
                writeItemValue(item, _oprot)
                _root_.scala.Some(QAndAAtom.ItemField)
              } else {
                _root_.scala.None
              }
            case 5 =>
              if (question.isDefined) {
                writeQuestionValue(question.get, _oprot)
                _root_.scala.Some(QAndAAtom.QuestionField)
              } else {
                _root_.scala.None
              }
            case _ => _root_.scala.None
          }
        _fieldOpt match {
          case _root_.scala.Some(_field) =>
            val _data = Arrays.copyOfRange(_buff.getArray, 0, _buff.length)
            _root_.scala.Some(TFieldBlob(_field, _data))
          case _root_.scala.None =>
            _root_.scala.None
        }
      }
    }
  }

  /**
   * Collects TCompactProtocol-encoded field values according to `getFieldBlob` into a map.
   */
  def getFieldBlobs(ids: TraversableOnce[Short]): immutable$Map[Short, TFieldBlob] =
    (ids flatMap { id => getFieldBlob(id) map { id -> _ } }).toMap

  /**
   * Sets a field using a TCompactProtocol-encoded binary blob.  If the field is a known
   * field, the blob is decoded and the field is set to the decoded value.  If the field
   * is unknown and passthrough fields are enabled, then the blob will be stored in
   * _passthroughFields.
   */
  def setField(_blob: TFieldBlob): QAndAAtom = {
    var typeLabel: _root_.scala.Option[String] = this.typeLabel
    var eventImage: _root_.scala.Option[com.gu.contentatom.thrift.Image] = this.eventImage
    var item: com.gu.contentatom.thrift.atom.qanda.QAndAItem = this.item
    var question: _root_.scala.Option[com.gu.contentatom.thrift.atom.storyquestions.Question] = this.question
    var _passthroughFields = this._passthroughFields
    _blob.id match {
      case 1 =>
        typeLabel = _root_.scala.Some(readTypeLabelValue(_blob.read))
      case 3 =>
        eventImage = _root_.scala.Some(readEventImageValue(_blob.read))
      case 4 =>
        item = readItemValue(_blob.read)
      case 5 =>
        question = _root_.scala.Some(readQuestionValue(_blob.read))
      case _ => _passthroughFields += (_blob.id -> _blob)
    }
    new Immutable(
      typeLabel,
      eventImage,
      item,
      question,
      _passthroughFields
    )
  }

  /**
   * If the specified field is optional, it is set to None.  Otherwise, if the field is
   * known, it is reverted to its default value; if the field is unknown, it is removed
   * from the passthroughFields map, if present.
   */
  def unsetField(_fieldId: Short): QAndAAtom = {
    var typeLabel: _root_.scala.Option[String] = this.typeLabel
    var eventImage: _root_.scala.Option[com.gu.contentatom.thrift.Image] = this.eventImage
    var item: com.gu.contentatom.thrift.atom.qanda.QAndAItem = this.item
    var question: _root_.scala.Option[com.gu.contentatom.thrift.atom.storyquestions.Question] = this.question

    _fieldId match {
      case 1 =>
        typeLabel = _root_.scala.None
      case 3 =>
        eventImage = _root_.scala.None
      case 4 =>
        item = null
      case 5 =>
        question = _root_.scala.None
      case _ =>
    }
    new Immutable(
      typeLabel,
      eventImage,
      item,
      question,
      _passthroughFields - _fieldId
    )
  }

  /**
   * If the specified field is optional, it is set to None.  Otherwise, if the field is
   * known, it is reverted to its default value; if the field is unknown, it is removed
   * from the passthroughFields map, if present.
   */
  def unsetTypeLabel: QAndAAtom = unsetField(1)

  def unsetEventImage: QAndAAtom = unsetField(3)

  def unsetItem: QAndAAtom = unsetField(4)

  def unsetQuestion: QAndAAtom = unsetField(5)


  override def write(_oprot: TProtocol): Unit = {
    QAndAAtom.validate(this)
    _oprot.writeStructBegin(Struct)
    if (typeLabel.isDefined) writeTypeLabelField(typeLabel.get, _oprot)
    if (eventImage.isDefined) writeEventImageField(eventImage.get, _oprot)
    if (item ne null) writeItemField(item, _oprot)
    if (question.isDefined) writeQuestionField(question.get, _oprot)
    if (_passthroughFields.nonEmpty) {
      _passthroughFields.values.foreach { _.write(_oprot) }
    }
    _oprot.writeFieldStop()
    _oprot.writeStructEnd()
  }

  def copy(
    typeLabel: _root_.scala.Option[String] = this.typeLabel,
    eventImage: _root_.scala.Option[com.gu.contentatom.thrift.Image] = this.eventImage,
    item: com.gu.contentatom.thrift.atom.qanda.QAndAItem = this.item,
    question: _root_.scala.Option[com.gu.contentatom.thrift.atom.storyquestions.Question] = this.question,
    _passthroughFields: immutable$Map[Short, TFieldBlob] = this._passthroughFields
  ): QAndAAtom =
    new Immutable(
      typeLabel,
      eventImage,
      item,
      question,
      _passthroughFields
    )

  override def canEqual(other: Any): Boolean = other.isInstanceOf[QAndAAtom]

  private def _equals(x: QAndAAtom, y: QAndAAtom): Boolean =
      x.productArity == y.productArity &&
      x.productIterator.sameElements(y.productIterator)

  override def equals(other: Any): Boolean =
    canEqual(other) &&
      _equals(this, other.asInstanceOf[QAndAAtom]) &&
      _passthroughFields == other.asInstanceOf[QAndAAtom]._passthroughFields

  override def hashCode: Int = _root_.scala.runtime.ScalaRunTime._hashCode(this)

  override def toString: String = _root_.scala.runtime.ScalaRunTime._toString(this)


  override def productArity: Int = 4

  override def productElement(n: Int): Any = n match {
    case 0 => this.typeLabel
    case 1 => this.eventImage
    case 2 => this.item
    case 3 => this.question
    case _ => throw new IndexOutOfBoundsException(n.toString)
  }

  override def productPrefix: String = "QAndAAtom"

  def _codec: ThriftStructCodec3[QAndAAtom] = QAndAAtom
}
  override def decode(_iprot: TProtocol): QAndAAtom =
    _iprot match {
      case i: LazyTProtocol => lazyDecode(i)
      case i => eagerDecode(i)
    }

  private[this] def eagerDecode(_iprot: TProtocol): QAndAAtom = {
    var typeLabel: _root_.scala.Option[String] = _root_.scala.None
    var eventImage: _root_.scala.Option[com.gu.contentatom.thrift.Image] = _root_.scala.None
    var item: com.gu.contentatom.thrift.atom.qanda.QAndAItem = null
    var _got_item = false
    var question: _root_.scala.Option[com.gu.contentatom.thrift.atom.storyquestions.Question] = _root_.scala.None
    var _passthroughFields: Builder[(Short, TFieldBlob), immutable$Map[Short, TFieldBlob]] = null
    var _done = false

    _iprot.readStructBegin()
    while (!_done) {
      val _field = _iprot.readFieldBegin()
      if (_field.`type` == TType.STOP) {
        _done = true
      } else {
        _field.id match {
          case 1 =>
            _field.`type` match {
              case TType.STRING =>
                typeLabel = _root_.scala.Some(readTypeLabelValue(_iprot))
              case _actualType =>
                val _expectedType = TType.STRING
                throw new TProtocolException(
                  "Received wrong type for field 'typeLabel' (expected=%s, actual=%s).".format(
                    ttypeToString(_expectedType),
                    ttypeToString(_actualType)
                  )
                )
            }
          case 3 =>
            _field.`type` match {
              case TType.STRUCT =>
                eventImage = _root_.scala.Some(readEventImageValue(_iprot))
              case _actualType =>
                val _expectedType = TType.STRUCT
                throw new TProtocolException(
                  "Received wrong type for field 'eventImage' (expected=%s, actual=%s).".format(
                    ttypeToString(_expectedType),
                    ttypeToString(_actualType)
                  )
                )
            }
          case 4 =>
            _field.`type` match {
              case TType.STRUCT =>
                item = readItemValue(_iprot)
                _got_item = true
              case _actualType =>
                val _expectedType = TType.STRUCT
                throw new TProtocolException(
                  "Received wrong type for field 'item' (expected=%s, actual=%s).".format(
                    ttypeToString(_expectedType),
                    ttypeToString(_actualType)
                  )
                )
            }
          case 5 =>
            _field.`type` match {
              case TType.STRUCT =>
                question = _root_.scala.Some(readQuestionValue(_iprot))
              case _actualType =>
                val _expectedType = TType.STRUCT
                throw new TProtocolException(
                  "Received wrong type for field 'question' (expected=%s, actual=%s).".format(
                    ttypeToString(_expectedType),
                    ttypeToString(_actualType)
                  )
                )
            }
          case _ =>
            if (_passthroughFields == null)
              _passthroughFields = immutable$Map.newBuilder[Short, TFieldBlob]
            _passthroughFields += (_field.id -> TFieldBlob.read(_field, _iprot))
        }
        _iprot.readFieldEnd()
      }
    }
    _iprot.readStructEnd()

    if (!_got_item) throw new TProtocolException("Required field 'item' was not found in serialized data for struct QAndAAtom")
    new Immutable(
      typeLabel,
      eventImage,
      item,
      question,
      if (_passthroughFields == null)
        NoPassthroughFields
      else
        _passthroughFields.result()
    )
  }

  def apply(
    typeLabel: _root_.scala.Option[String] = _root_.scala.None,
    eventImage: _root_.scala.Option[com.gu.contentatom.thrift.Image] = _root_.scala.None,
    item: com.gu.contentatom.thrift.atom.qanda.QAndAItem,
    question: _root_.scala.Option[com.gu.contentatom.thrift.atom.storyquestions.Question] = _root_.scala.None
  ): QAndAAtom =
    new Immutable(
      typeLabel,
      eventImage,
      item,
      question
    )

  def unapply(_item: QAndAAtom): _root_.scala.Option[_root_.scala.Tuple4[Option[String], Option[com.gu.contentatom.thrift.Image], com.gu.contentatom.thrift.atom.qanda.QAndAItem, Option[com.gu.contentatom.thrift.atom.storyquestions.Question]]] = _root_.scala.Some(_item.toTuple)


  @inline private def readTypeLabelValue(_iprot: TProtocol): String = {
    _iprot.readString()
  }

  @inline private def writeTypeLabelField(typeLabel_item: String, _oprot: TProtocol): Unit = {
    _oprot.writeFieldBegin(TypeLabelField)
    writeTypeLabelValue(typeLabel_item, _oprot)
    _oprot.writeFieldEnd()
  }

  @inline private def writeTypeLabelValue(typeLabel_item: String, _oprot: TProtocol): Unit = {
    _oprot.writeString(typeLabel_item)
  }

  @inline private def readEventImageValue(_iprot: TProtocol): com.gu.contentatom.thrift.Image = {
    com.gu.contentatom.thrift.Image.decode(_iprot)
  }

  @inline private def writeEventImageField(eventImage_item: com.gu.contentatom.thrift.Image, _oprot: TProtocol): Unit = {
    _oprot.writeFieldBegin(EventImageField)
    writeEventImageValue(eventImage_item, _oprot)
    _oprot.writeFieldEnd()
  }

  @inline private def writeEventImageValue(eventImage_item: com.gu.contentatom.thrift.Image, _oprot: TProtocol): Unit = {
    eventImage_item.write(_oprot)
  }

  @inline private def readItemValue(_iprot: TProtocol): com.gu.contentatom.thrift.atom.qanda.QAndAItem = {
    com.gu.contentatom.thrift.atom.qanda.QAndAItem.decode(_iprot)
  }

  @inline private def writeItemField(item_item: com.gu.contentatom.thrift.atom.qanda.QAndAItem, _oprot: TProtocol): Unit = {
    _oprot.writeFieldBegin(ItemField)
    writeItemValue(item_item, _oprot)
    _oprot.writeFieldEnd()
  }

  @inline private def writeItemValue(item_item: com.gu.contentatom.thrift.atom.qanda.QAndAItem, _oprot: TProtocol): Unit = {
    item_item.write(_oprot)
  }

  @inline private def readQuestionValue(_iprot: TProtocol): com.gu.contentatom.thrift.atom.storyquestions.Question = {
    com.gu.contentatom.thrift.atom.storyquestions.Question.decode(_iprot)
  }

  @inline private def writeQuestionField(question_item: com.gu.contentatom.thrift.atom.storyquestions.Question, _oprot: TProtocol): Unit = {
    _oprot.writeFieldBegin(QuestionField)
    writeQuestionValue(question_item, _oprot)
    _oprot.writeFieldEnd()
  }

  @inline private def writeQuestionValue(question_item: com.gu.contentatom.thrift.atom.storyquestions.Question, _oprot: TProtocol): Unit = {
    question_item.write(_oprot)
  }


  object Immutable extends ThriftStructCodec3[QAndAAtom] {
    override def encode(_item: QAndAAtom, _oproto: TProtocol): Unit = { _item.write(_oproto) }
    override def decode(_iprot: TProtocol): QAndAAtom = QAndAAtom.decode(_iprot)
    override lazy val metaData: ThriftStructMetaData[QAndAAtom] = QAndAAtom.metaData
  }

  /**
   * The default read-only implementation of QAndAAtom.  You typically should not need to
   * directly reference this class; instead, use the QAndAAtom.apply method to construct
   * new instances.
   */
  class Immutable(
      val typeLabel: _root_.scala.Option[String],
      val eventImage: _root_.scala.Option[com.gu.contentatom.thrift.Image],
      val item: com.gu.contentatom.thrift.atom.qanda.QAndAItem,
      val question: _root_.scala.Option[com.gu.contentatom.thrift.atom.storyquestions.Question],
      override val _passthroughFields: immutable$Map[Short, TFieldBlob])
    extends QAndAAtom {
    def this(
      typeLabel: _root_.scala.Option[String] = _root_.scala.None,
      eventImage: _root_.scala.Option[com.gu.contentatom.thrift.Image] = _root_.scala.None,
      item: com.gu.contentatom.thrift.atom.qanda.QAndAItem,
      question: _root_.scala.Option[com.gu.contentatom.thrift.atom.storyquestions.Question] = _root_.scala.None
    ) = this(
      typeLabel,
      eventImage,
      item,
      question,
      Map.empty
    )
  }

  /**
   * This is another Immutable, this however keeps strings as lazy values that are lazily decoded from the backing
   * array byte on read.
   */
  private[this] class LazyImmutable(
      _proto: LazyTProtocol,
      _buf: Array[Byte],
      _start_offset: Int,
      _end_offset: Int,
      typeLabelOffset: Int,
      val eventImage: _root_.scala.Option[com.gu.contentatom.thrift.Image],
      val item: com.gu.contentatom.thrift.atom.qanda.QAndAItem,
      val question: _root_.scala.Option[com.gu.contentatom.thrift.atom.storyquestions.Question],
      override val _passthroughFields: immutable$Map[Short, TFieldBlob])
    extends QAndAAtom {

    override def write(_oprot: TProtocol): Unit = {
      _oprot match {
        case i: LazyTProtocol => i.writeRaw(_buf, _start_offset, _end_offset - _start_offset)
        case _ => super.write(_oprot)
      }
    }

    lazy val typeLabel: _root_.scala.Option[String] =
      if (typeLabelOffset == -1)
        None
      else {
        Some(_proto.decodeString(_buf, typeLabelOffset))
      }

    /**
     * Override the super hash code to make it a lazy val rather than def.
     *
     * Calculating the hash code can be expensive, caching it where possible
     * can provide significant performance wins. (Key in a hash map for instance)
     * Usually not safe since the normal constructor will accept a mutable map or
     * set as an arg
     * Here however we control how the class is generated from serialized data.
     * With the class private and the contract that we throw away our mutable references
     * having the hash code lazy here is safe.
     */
    override lazy val hashCode = super.hashCode
  }

  /**
   * This Proxy trait allows you to extend the QAndAAtom trait with additional state or
   * behavior and implement the read-only methods from QAndAAtom using an underlying
   * instance.
   */
  trait Proxy extends QAndAAtom {
    protected def _underlying_QAndAAtom: QAndAAtom
    override def typeLabel: _root_.scala.Option[String] = _underlying_QAndAAtom.typeLabel
    override def eventImage: _root_.scala.Option[com.gu.contentatom.thrift.Image] = _underlying_QAndAAtom.eventImage
    override def item: com.gu.contentatom.thrift.atom.qanda.QAndAItem = _underlying_QAndAAtom.item
    override def question: _root_.scala.Option[com.gu.contentatom.thrift.atom.storyquestions.Question] = _underlying_QAndAAtom.question
    override def _passthroughFields = _underlying_QAndAAtom._passthroughFields
  }
}

Shapeless

  • Library for generic programming in Scala
  • Leverages the similarities between types
case class Employee(name: String,         age: Int, manager: Boolean)​
case class IceCream(name: String, numCherries: Int,  inCone: Boolean)​
String :: Int :: Boolean :: HNil

HList

Generic[IceCream].to(iceCream)
Generic[Employee].to(employee)

First approach

case class Atom(
    id: String, 
    atomType: String, 
    title: String, 
    data: AtomData)

sealed trait AtomData
object AtomData {
  case class Media(media: MediaAtom) extends AtomData
  case class Explainer(explainer: ExplainerAtom) extends AtomData
}

case class MediaAtom(
    url: String, 
    metadata: Option[Metadata])
case class ExplainerAtom(
    headline: String, 
    body: String)

case class Metadata(
    commentsEnabled: Option[Boolean], 
    channelId: Option[String])

First approach

val genericRepr = LabelledGeneric[Atom].to(mediaAtom) 
// "123" :: "media" :: "Scala fun" :: Media(MediaAtom(...)) :: HNil
PATCH /api/media/123/title
body: "Updated title"
val updatedGeneric = genericRepr + (Symbol("title") ->> "Updated title")) 
// "123" :: "media" :: "Updated title" :: Media(MediaAtom(...)) :: HNil
val mediaAtom = Atom(
    id = "123", 
    atomType = "media", 
    title = "Scala fun", 
    data = AtomData.Media(MediaAtom(
        url = "gu.com",
        metadata = Some(Metadata( 
            commentsEnabled = Some(true), 
            channelId = Some("programming"))))))

First approach

val genericRepr = LabelledGeneric[Atom].to(mediaAtom) 
// "123" :: "media" :: "Scala fun" :: Media(MediaAtom(...)) :: HNil
PATCH /api/media/123/data.metadata.channelId
body: "Scala"
val updatedGeneric2 = genericRepr + (Symbol(nestedField) ->> "Updated field"))
// error: Expression scala.Symbol.apply(ScalaFiddle.this.nestedField) does 
// not evaluate to a constant or a stable reference value
val nestedField = "data.metadata.channelId"
val mediaAtom = Atom(
    id = "123", 
    atomType = "media", 
    title = "Scala fun", 
    data = AtomData.Media(MediaAtom(
        url = "gu.com",
        metadata = Some(Metadata( 
            commentsEnabled = Some(true), 
            channelId = Some("programming"))))))

Second approach

Nested Map[String, Any]

Update the field in the map

HList

HList

Type Classes

trait Greetings[A] {
  def message(creature: A): String
}

object Greetings {
    implicit def humanMessage: Greetings[Human] = 
        (human: Human) => s"${human.name} says hello."
    
    implicit def catMessage: Greetings[Cat] = 
        (cat: Cat) => s"${cat.name} says meow."

    implicit class GreetingsOps[A](creature: A) {
        def greet(implicit greetings: Greetings[A]) = {
          greetings.message(creature)
        }
    }
}

Human("Maria").greet 
// "Maria says hello."
Cat("Mistoffelees").greet 
// "Mistoffelees says meow."
Dog("Pollicle").greet 
// error: could not find implicit value for parameter message


Case class => Map[String,Any]

trait ToMapRec[L <: HList] {
  def apply(l: L): Map[String, Any]
}
"1234567" :: Some("media") :: "Scala fun" :: Media(MediaAtom(...)) :: HNil

...

// Implicits:

HNil
FieldType[K, Option[H]] :: T
FieldType[K, Seq[H]] :: T
FieldType[K, H] :: T // Where the head can be recursively converted
FieldType[K, H] :: T // Where the head can NOT be recursively converted (low priority)

Case class => Map[String,Any]

trait ToMapRec[L <: HList] {
  def apply(hlist: L): Map[String, Any]
}

...

implicit def hconsToMapRecOption[K <: Symbol, V, H <: HList, T <: HList]
(implicit
 wit: Witness.Aux[K],
 gen: LabelledGeneric.Aux[V, H],
 tmrT: Lazy[ToMapRec[T]],
 tmrH: Lazy[ToMapRec[H]]
): ToMapRec[FieldType[K, Option[V]] :: T] = ???

...

Case class => Map[String,Any]

trait ToMapRec[L <: HList] {
  def apply(hlist: L): Map[String, Any]
}

...

implicit def hconsToMapRecOption[K <: Symbol, V, H <: HList, T <: HList]
(implicit
 wit: Witness.Aux[K],
 gen: LabelledGeneric.Aux[V, H],
 tmrT: Lazy[ToMapRec[T]],
 tmrH: Lazy[ToMapRec[H]]
): ToMapRec[FieldType[K, Option[V]] :: T] = 

    (hlist: FieldType[K, Option[V]] :: T) =>

        tmrT.value(hlist.tail) + 
        (wit.value.name -> hlist.head.map(value => tmrH.value(gen.to(value))))

Case class => Map[String,Any]

...

  implicit class ToMapRecOps[A](val a: A) extends AnyVal {
    def toMap[L <: HList]
    (implicit
     gen: LabelledGeneric.Aux[A, L],
     tmr: Lazy[ToMapRec[L]]
    ): Map[String, Any] = tmr.value(gen.to(a))
  }

val atomDataMap = atomData.toMap
val atomDataMap = Map(
  "metadata" -> Some(Map(
    "commentsEnabled" -> Some(false), 
    "channelId" -> Some("programming"))), 
  "url" -> "gu.com")
[error] could not find implicit value for parameter 
gen: shapeless.LabelledGeneric.Aux[com.gu.contentatom.thrift.AtomData,L]

Fixing Thrift

def helperLabelledGeneric[A, I <: A, L <: HList]
(implicit gen: LabelledGeneric.Aux[I, L])
: LabelledGeneric.Aux[A, L] =
    new LabelledGeneric[A] {
      override type Repr = L
      override def to(t: A): Repr = gen.to(t.asInstanceOf[I])
      override def from(r: Repr): A = gen.from(r)
    }
implicit def atomDataLabelledGeneric[L <: HList]
(implicit gen: LabelledGeneric.Aux[AtomData.Immutable, L])
: LabelledGeneric.Aux[AtomData, L] =
    helperLabelledGeneric[AtomData, AtomData.Immutable, L]

...

Map[String,Any] => Case class

// Implicits:

HNil
FieldType[K, Option[H]] :: T
FieldType[K, Seq[H]] :: T
FieldType[K, H] :: T // Where the head can be recursively converted
FieldType[K, H] :: T // Where the head can NOT be recursively converted (low priority)
trait FromMap[L <: HList] {
    def apply(m: Map[String, Any]): Option[L]
}

Map[String,Any] => Case class

trait FromMap[L <: HList] {
    def apply(m: Map[String, Any]): Option[L]
}
...

implicit def hconsFromMapOption[K <: Symbol, V, R <: HList, T <: HList]
(implicit
 witness: Witness.Aux[K],
 gen: LabelledGeneric.Aux[V, R],
 fromMapH: Lazy[FromMap[R]],
 fromMapT: Lazy[FromMap[T]]
): FromMap[FieldType[K, Option[V]] :: T] = (m: Map[String, Any]) =>
  m(witness.value.name) match {
    case Some(v) =>
      for {
        r <- Typeable[Option[Map[String, Any]]].cast(Some(v))
        h <- r.map(fromMapH.value(_))
        t <- fromMapT.value(m)
      } yield field[K](h.map(gen.from)) :: t
    case None =>
      for {
        t <- fromMapT.value(m)
      } yield field[K](None) :: t
  }

...

Map[String,Any] => Case class

...

implicit class FromMapOps[A] {
    def from[R <: HList](m: Map[String, Any])
    (implicit gen: LabelledGeneric.Aux[A, R],
     fromMap: Lazy[FromMap[R]]
    ): Option[A] = fromMap.value(m).map(gen.from)
}

val atom: Atom = to[Atom.Immutable].from(updatedAtom)

Final approach

Json + Circe

Circe

PATCH /api/media/some-id
body:
{
    "data": {
        "metadata": {
            "channelId": "Scala"
        }
    }
}
val atomJson = atom.toJson
atomJson.deepMerge(bodyJson)

Bonus: Magnolia

import magnolia._
import scala.language.experimental.macros

trait ToMapMagnolia[T] {
  def apply(arg: T) : Any
}

object ToMapMagnolia {
  type Typeclass[T] = ToMapMagnolia[T]

  def combine[T](caseClass: CaseClass[Typeclass, T]): Typeclass[T] = 
    (instance: T) => caseClass.parameters.map(param => 
        param.label -> {param.typeclass(param.dereference(instance))}).toMap

  def dispatch[T](sealedTrait: SealedTrait[Typeclass, T]): Typeclass[T] = 
    (instance: T) => sealedTrait.dispatch(instance)(subType => 
        subType.typeclass.apply(subType.cast(instance)))

  implicit def baseCase[T <: AnyVal]: ToMapMagnolia[T] = (x: T) => x
  implicit def stringCase: ToMapMagnolia[String] = x => x

  implicit def optCase[T](implicit tm: Typeclass[T]): Typeclass[Option[T]] = _.map(tm.apply)
  implicit def seqCase[T](implicit tm: Typeclass[T]): Typeclass[Seq[T]] = _.map(tm.apply)
  
  implicit def gen[T]: Typeclass[T] = macro Magnolia.gen[T]

  implicit class ToMapOps[A](a: A) {
    def toMapMagnolia(implicit tm: ToMapMagnolia[A]): Any = tm(a)
  }
}

Summary

Thank you.

The Path to Generic Endpoints using Shapeless

By Maria Livia

The Path to Generic Endpoints using Shapeless

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