1. Preamble

This guide is intended for developers that want to maintain, enhance and extend the Tensei-Data system. It is also feasible for administrators that strive for a better understanding of the system internals.



For this guide it is assumed that you run the components of the Tensei-Data system directly from their source repositories.
Copyright (c) 2014 - 2017 Contributors as noted in the AUTHORS.md file

The Tensei-Data developer guide is distributed under the terms of the
Creative Commons Attribution-ShareAlike 4.0 International license
(CC BY-SA 4.0).

1.2. Authors

The following authors contributed to this guide:

Corporate Contributors

- Copyright (c) 2014 - 2015 Wegtam UG (haftungsbeschränkt)
- Copyright (c) 2015 - 2017 Wegtam GmbH

Individual Contributors

- Jens Grassel
- André Schütz

2. Introduction

To develop with the Tensei-Data system you will need knowledge in Scala [1], preferably Akka [2] and maybe the Play Framework [3] and Javascript/Coffeescript [4].

2.1. Running from source

Running the components directly from source is simple: Just checkout the following repositories (better your fork of them):

  • tensei-agent

  • tensei-frontend

  • tensei-server

Within each repository compile the sources using the appropriate sbt task (compile). To start a component just use the run task.

You should always start the Tensei-Server first!

3. Extending Tensei-Data

3.1. Adding a transformer

A transformer is defined as an actor that extends the BaseTransformer class which can be found under com.wegtam.tensei.agent.transformers.

Besides the general transformers there are atomic transformers. An atomic transformer performs its action before the general transformers are run.

There is no difference regarding the implementation between atomic and regular transformers.

3.1.1. Implementing your transformer

Start by creating a class which extends the aforementioned BaseTransformer and implement the method transform. The general workflow is as follows:

  1. A transformer is created and initialised using the message PrepareForTransformation on which it switches context using context.become(transform) and returns the message ReadyToTransform. This is already implemented by the base transformer.

  2. The ready transformer receives a message StartTransformation which contains the data to transform and the options.

  3. After successful operation the transformer responds with a TransformerResponse message and switches the context back by context.become(receive).

To ease testing it is advised to implement the core transformation functions either in the companion object or in a trait.
Akka props

Within the companion object you have to define the method props which returns the properties needed by Akka to create the actor. Since a transformer should not use constructor parameters this is as trivial as this:

Define actor props for Akka
import akka.actor.Props

object MyTransformerName {
  def props: Props = Props(new MyTransformerName())
Actor implementation

In general you only have to implement the remaining workflow steps within the actors transform method. For extracting settings from the given options you can use some functions defined in the base transformer like paramValueO, paramValue or isCorrectParameter.

Example transformer
import akka.actor.Props
import com.wegtam.tensei.agent.transformers.BaseTransformer.{

class MyTransformerName extends BaseTransformer {
  override def transform: Receive = {
    case StartTransformation(src, options) =>
      log.debug("Starting MyTransformerName transformation.")
      val settingOne: Int = paramValueO("settingOneName")(options.params)
        .map(_.toInt).getOrElse(0) (1)
      val settingTwo: String = paramValue("settingTwoName")(options.params)

      val result = src.map {
        case t: MyDataType => MyTransformerName.myConvert(t)
        case otherDataType => otherDataType

      sender() ! TransformerResponse(result, classOf[String])

object MyTransformerName {
  def props: Props = Props(new MyTransformerName())

  def myConvert(t: MyDataType): AnotherDataType = ???
1 This line will crash the actor if .toInt throws an exception.
If your transformer is unable to handle certain usecases which result from operating it on irrational input let it crash.
Testing your transformer

Write tests for your transformer which include possible edge or special cases as well as general behaviour. Regarding the general behaviour the following is expected:

  1. When given no data the actor should return an empty list.

  2. When given one value the actor should return a list with one result.

  3. When given multiple values the actor should return list with the results.

  4. When given invalid options it should either use sensible defaults or crash.

Additionally test your conversion functions for the mentioned edge/special cases.

Use the PropertyChecks trait from ScalaTest to be able to leverage ScalaCheck for massive input data generation and property based tests.

3.1.2. Adding your transformer to the frontend

Without adding your transformer to the editor (frontend) it will be invisible and thus unuseable for the user.

Adding a new transformer to the editor is straightforward you only need to provide serveral informations:

  1. localisation messages for your settings

  2. description of the transformer settings and class

  3. a template for the settings form


The localisation messages are kept in the file conf/messages and provide a simple key value mapping. By convention localisation keys for transformer settings follow this pattern: ui.mappings.transformer.transformerName.settingsName.


The file editor-controllers.coffee under app/assets/javascripts contains the relevant code.

At first you should add your transformer to the field selectedTransformerIs which is used to initialise the form. It contains a list of transformer names which are mapped to false.

  selectedTransformerIs: (->
    ts = {
      CastStringToLong: false,
      Concat: false,
      MyTransformerName: false

Next the field availableTransformerOptions contains objects that describe the available settings for each transformer. You can use the attribute options to provide a fixed list of values for a dropdown field. The attribute value can be used to define the default value. Setting value to null results in no predefined default.

Defining an empty object means that the transformer has no settings.

    AnExampleTransformerWithoutSettings: {},
    MyTransformerName: {
      settingNameOne: {
        options: null,
        value: "Some text"
      settingNameTwo: {
        options: null,
        value: ""
      settingNameThree: {
        options: ["A", "B", "C"],
        value: null

Last but not least you have to add your transformer to the two fields availableTransformations and availableTransformationsClassNames. The former holds a list of transformer names that are displayed in the form dropdown when adding a transformer. The latter is used to map the transformer name to the class name which is needed by the agent to initialise the transformer properly.

  availableTransformations: [
  availableTransformationsClassNames: {
    "CastStringToLong": "com.wegtam.tensei.agent.transformers.CastStringToLong",
    "MyTransformerName": "com.wegtam.tensei.agent.transformers.MyTransformerName"
Settings Template

The form template for your transformer settings has to be defined in editor.scala.html which resides under app/views/cookbookresources.

Depending on the type of your transformer you have to add it to the div with the id transformations and (only for atomic transformers!) to the div with the id atomictransformations.

At the mentioned places you will find an if construct which has to be extended to render your template partial there.

  {{else if selectedTransformerIs.TimestampCalibrate}}
    {{partial 'transformer-settings-timestamp-calibrate'}}
  {{else if selectedTransformerIs.MyTransformerName}}
    {{partial 'transformer-settings-my-transformer-name'}}
    <p class="alert alert-danger">


At the bottom of the file you’ll find handlebars templates for each transformers settings. Just create your own one by learning from the existing ones.

Example settings template
<script type="text/x-handlebars"
    <table class="table table-condensed">
          <td>{{view "select" class="form-control input-sm"
          <td>{{input class="form-control input-sm"

Congratulations, your transformer should now be visible and useable from the frontend cookbook editor.

1. Scala Programming Language: http://scala-lang.org
2. Akka Toolkit: http://akka.io
3. Play Framework: https://playframework.com/
4. Coffeescript: http://coffeescript.org