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POC for modifying the underlying data for a tableau report from a web page using the JS API
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README.md

Quickstart

Pre-requisites

npm install
npm install gulp --global

Install the index.html file found in _public to your Tableau Server as a web data connector (but change the address for the javascript and css files used to point to your local server).

After the web data connector is installed, set the URL of Published HTML file parameter in the test workbook to point to the newly installed web data connector. This allow the dashboard to load the web data connector to the right side of the screen, which in turn forwards the requests to your development server.

A detailed explanation of this installation process can be found in the Tableau JavaScript API without Embedding blog post.

Running the server

gulp watch serve

Executive Summary

This is a Proof-of-Concept showing how to use the Tableau JS API to add annotations to and modify the underlying data of a Tableau workbook from your web browser.

The data

The data represents trading good prices in the galaxy (using Elite: Dangerous rare goods as a basis, but the data itself is just a lowpassed random series swifting around the base price.)

Its hierarchy is like:

  • There are Systems in the Galaxy
  • There are Stations or Ports in the Systems
  • Each station in the dataset has goods only available there (rare goods) whose price fluctuates.

The structure of the data in the database is very simple and denormalized:

drop table if exists sales_by_month;
create table if not exists sales_by_month (
  id serial not null primary key,
  system_name text,
  port_location text,

  product_name text,

  month_start date,

  quantity numeric(10,0),
  unit_price numeric(10,2),

  comment text
);

A generated base dataset is available in app/sql/goods_list.csv.

The server-side

Our server needs to connect to the backing PostgreSQL database and update the comment and quantity fields if the user requests.

We'll use Node.js to build this server.

Connect to the database

We'll use the NodeJS PostgreSQL driver to connect to the backing database.

npm install pg --save

Lets add the requires we'll need for the postgres connection and write a basic connection pool for our webapp (this is pretty much copy-paste from the Node.js Postgres example:

pg = require 'pg'


client = new pg.Client()

# note: all config is optional and the environment variables
# will be read if the config is not present
config =
  user: 'testuser', #env var: PGUSER
  database: 'testuser', #env var: PGDATABASE
  password: 'test123', #env var: PGPASSWORD
  host: '52.44.214.221', # Server hosting the postgres database
  port: 5432, #env var: PGPORT
  max: 10, # max number of clients in the pool
  idleTimeoutMillis: 30000, # how long a client is allowed to remain idle before being closed

process.on 'unhandledRejection', (e)->
  console.error("Node 'unhandledRejection':", e.message, e.stack)


# this initializes a connection pool
# it will keep idle connections open for a 30 seconds
# and set a limit of maximum 10 idle clients
pool = new pg.Pool(config)

pool.on 'error', (err, client)->
  console.error('Postgres idle client error', err.message, err.stack)

So now we have a connection pool to the postgres database. Lets write a quick helper to run a query and return a promise. We'll use the Bluebird JS Promise library for the Promises.

npm install bluebird --save
Promise = require 'bluebird'

q = (query, opts=[])->
  new Promise (resolve, reject)->
    pool.query query, opts, (err, res)->
      return reject(err) if err
      resolve(res)

Create the server

Now that the database connection is set up, lets add the HTTP server bits. We'll be using the ExpressJS framework to implement this:

npm install express --save
express = require 'express'
app = express()

server_config =
  port: 9999
  address: "0.0.0.0"


# Use the '_public' folder as static document root
app.use express.static('_public')

# Handler for updating the comment/quantity on a row
app.get '/update-comment/:id', (req, res)->
  # [...]

app.listen server_config.port, server_config.address, ()->
  console.log("Test app listening on port #{server_config.port}!")

This should be fairly trivial:

  • we import express and create an instance that will be our application
  • we set the _public folder as our static document root and server static files from there
  • we create a handler that changes the comment for a row
  • then start the server by binding it to the port and address specified by the config.

The update handler

Now lets write the handler that updates the database.

  • This handler gets an id in the URL plus a quantity and a comment field in the request body.
  • Using this id and attributes, it updates the record then responds with an "OK" or an "ERROR"
app.get '/update-comment/:id', (req, res)->
  {quantity, comment} = req.query
  q( "UPDATE sales_by_month SET quantity=$2, comment=$3 WHERE id=$1", [req.params.id, quantity, comment])
    .then (e)-> res.json("OK")
    .error (err)->
      console.error err.message, err.stack
      res.status(500).json("ERROR")

Cross-origin requests

Since our web server will be responding to a web page under a different domain, we'll need to emit proper CORS headers so browsers accept our responses. Doing this in Express is very easy:

npm install cors --save

Then add the cors to the application as middleware:

cors = require('cors')

app.use(cors())

This completes our server.

The client side

Lets look at the logic on the client side:

  • On load it should tell us to select a commodity from the Tableau report.

  • If we click on any point in the price graphs, a form should be displayed allowing us to add/change/clear the comment and the quantity in the underlying data in the database at that point

  • After submitting the form, the database should be updated and the Tableau report should be refreshed to reflect the changes made.

Creating the form and the "select" message

We'll put this form directly into the Web Data Connector HTML file:

  <div class="container">

    <div id="editor-wrap"  style='display:none;'>

      <div class="row">
        <div class="col-sm-12">
          <div id="intro-text">
            <h3>Edit the selected data</h3>
            <p>
            </p>
          </div>
        </div>
      </div>

      <div class="row">
        <div class="col-sm-12">

          <!-- The actual editor form -->
          <div class='editor-form-wrap'>
            <form id="editor-form">

              <input type="hidden" name="id" value="" />

              <table class='table table-condensed info-table'>
                <tbody>
                  <tr>
                    <th>System name</th>
                    <td data-field="system_name"><td>
                  </tr>
                  <tr>
                    <th>Port location</th>
                    <td data-field="port_location"><td>
                  </tr>
                  <tr>
                    <th>Month start</th>
                    <td data-field="month_start"><td>
                  </tr>
                  <tr>
                    <th>Unit price</th>
                    <td>$<span data-field="unit_price"></span><td>
                  </tr>

                  <tr>
                    <th>
                      <label for="quantity-input">Quantity</label>
                    </th>
                    <td>
                      <input type="number" class="form-control" id="quantity-input" name='quantity' placeholder="New quantity">
                    </td>
                  </tr>

                  <tr>
                    <th>
                      <label for="comment-input">Comment for this point</label>
                    </th>
                    <td >
                      <textarea name='comment' placeholder='Add a comment...' id='comment-input' class='form-control'></textarea>
                    </td>
                  </tr>

                </tbody>
              </table>


              <a href="#" class="btn btn-default" data-submit="true" data-url="http://52.44.214.221:9999/update-comment/{{id}}">Submit</a>

            </form>
          </div>

        </div>
      </div>
    </div>

    <div id='nodata-wrap'>
      <div class="row">
        <div class="col-sm-12">
          <div id="intro-text">
            <h3>Select a data point</h3>
            <p>
              To edit the data and the comments
            </p>
          </div>
        </div>
      </div>

    </div>

  </div>

Form helper for easy back-and-forth

Then lets create some helper for dealing with this form:

# Updates form fields in parent selector from a hash of name => value
# pairs
updateFormFields = (parent, data)->
  $parent = $(parent)
  for k,v of data
    # Skip the tableau %null%-S
    v = "" if v == TABLEAU_NULL
    $("input[name=#{k}], textarea[name=#{k}]", $parent.el).val(v)
    $("[data-field=#{k}]", $parent.el).text(v)

This function takes a jquery selector and a javascript object and sets the values/contents of each form and html element with a corresponding name or data-field attribute.

getFormFields = (parent)->
  o = {}
  $("input, textarea, [data-field]").each ()->
    $t = $(this)
    o[$t.attr('name')] = $t.val()
  o

This function does the exact inverse: it collects all data from the elements in the form.

More form helpers for showing/hiding

To be able to show/hide the form and the 'Select a product' message, lets add some helpers

EDITOR_SELECTOR = "#editor-wrap"
NODATA_SELECTOR = "#nodata-wrap"

showEditor = ()-> $(NODATA_SELECTOR).hide(100, ()-> $(EDITOR_SELECTOR).show())
hideEditor = ()-> $(EDITOR_SELECTOR).hide(100, ()-> $(NODATA_SELECTOR).show())
toggleEditor = (show)-> if show then showEditor() else hideEditor()

While we are at the form, lets also create a function that sets up the submit action to map to our submit handler function.

initEditorForm = (selector)->
  $editorForm = $(selector)
  $("[data-submit=true]", $editorForm.el).click submitForm
  $editorForm

We'll come back to this submitForm function later when we submit the form.

Connect to the Tableau JS API

Lets define a few functions that allow us to connect to the tableau JS API in the dashboard frame while keeping line lengths sane (this process has been explained in detail in the Tableau JavaScript API without Embedding blog post).

# Quick accessors for accessing the tableau bits on the parent page
getTableau = ()-> parent.parent.tableau
getCurrentViz = ()-> getTableau().VizManager.getVizs()[0]

# Returns the current worksheet.
# The path to access the sheet is hardcoded for now.
getCurrentWorksheet = ()-> getCurrentViz().getWorkbook().getActiveSheet().getWorksheets()[0]

We also need to export our initializer function so it can be ran on document load:

@appApi = {
  initEditor
}

Create some helpers

Also lets declare a simple helper that wraps a function in a try/catch block, so any exceptions wont be swallowed by the JS Promise implementation used:

# Because handlers in promises swallow errors and
# the error callbacks for Promises/A are flaky,
# we simply use this function to wrap calls
errorWrapped = (context, fn)->
  (args...)->
    try
      fn(args...)
    catch err
      console.error "Got error during '", context, "' : ", err.message, err.stack

Set up an event handler

We want to show the comment / value form when the user selects a point on our dashboard. To do this, we'll hook into the Tableau MARKS_SELECTION event.

initEditor = ->
  # Setup the editor form
  $editorForm = initEditorForm("#editor-form")

  # Get the tableau bits from the parent.
  tableau = getTableau()

  # Error handler in case getting the data fails in the Promise
  onDataLoadError = (err)->
    console.err("Error during Tableau Async request:", err)

  # Handler for loading and converting the tableau data to chart data
  onDataLoadOk = errorWrapped "Getting data from Tableau", (table)-> # [...]

  # Handler that gets the selected data from tableau and sends it to the form
  # display function
  updateEditor = ()->
    getCurrentWorksheet()
      .getUnderlyingDataAsync({maxRows: 1, ignoreSelection: false, includeAllColumns: true, ignoreAliases: true})
      .then(onDataLoadOk, onDataLoadError )

  # Add an event listener for marks change events that simply loads the
  # selected data to the chart
  getCurrentViz().addEventListener( tableau.TableauEventName.MARKS_SELECTION,  updateEditor)


@appApi = {
  initEditor
}

Lets walk through the important bits of code from the back

getCurrentViz().addEventListener( tableau.TableauEventName.MARKS_SELECTION,  updateEditor)

This tells Tableau to call updateEditor on selecting anything on the dashboard.

  updateEditor = ()->
    getCurrentWorksheet()
      .getUnderlyingDataAsync({maxRows: 1, ignoreSelection: false, includeAllColumns: true, ignoreAliases: true})
      .then(onDataLoadOk, onDataLoadError )

We use the Tableau JS API to get the underlying data:

  • we DO want all columns not just the displayed ones
  • we DONT care about aliases, we dont use them in our workbook
  • we DO only care about the data related to the selection
  • we ONLY want the first row from the underlying data (if we select a complete row, we want to ignore that selection)

getUnderlyingDataAsync() returns a Promise we need to handle, .then is the Promise way of saying:

  • if the everything went OK, call onDataLoadOk with the loaded data
  • if anything failed, call onDataLoadError with the exception (where we simply log it to the console)

Converting Tableau data to JavaScript data

So lets assume that the request for the underlying data was successful and Tableau calls us back with the data. Its in Tableau's own format (an array of Tableau objects), so lets convert it to a native POD (plain old data) format.

Getting the column indices

Tableau needs column indices instead of column names, which is very uncomfortable and error prone, so lets do two little helper functions:

The first one takes a tableau table and a list of column names we are interested in and returns a javascript object where the keys are the field names we've given and the values are the field indices:

# Takes a table and returns a "COLUMN_NAME" => COLUMN_IDX map
getColumnIndexes = (table, required_keys)->
  # Create a column name -> idx map
  colIdxMaps = {}
  for c in table.getColumns()
    fn = c.getFieldName()
    if fn in required_keys
      colIdxMaps[fn] = c.getIndex()
  colIdxMaps

The second helper takes a Tableau Row object and the fieldname/index map object returned by getColumnIndexes() and returns a POD javascript object with the field names mapped to the values using _.mapObject():

# Takes a Tableau Row and a "COL_NAME" => COL_IDX map and returns
# a new object with the COL_NAME fields set to the corresponding values
convertRowToObject = (row, attrs_map)->
  _.mapObject attrs_map, (id, name)-> row[id].value

Filling the form

Lets write the first steps of the onDataLoadOk function using the helpers we have created:

# Handler for loading and converting the tableau data to chart data
onDataLoadOk = errorWrapped "Getting data from Tableau", (table)->
    # Decompose the ids
    col_indexes = getColumnIndexes(table, ["id", "month_start", "system_name", "port_location", "product_name", "quantity", "unit_price", "comment"])

    data = table.getData()

    # Show-hide the editor if we have data
    toggleEditor(data.length == 1)

    graphData = _.first( _.map(table.getData(), (row)-> convertRowToObject(row, col_indexes)))

    errorWrapped( "Updating form fields", updateFormFields)( $editorForm, graphData )

With the helpers we've written this function should be fairly trivial to understand:

  • get the column indexes for the properties we care about
  • transform the Tableau row(s) into javascript POD rows and take only the first of them
  • then update the form to set all inputs/fields to the proper value

Submitting the form

In our initEditorForm() function we have assgined a submission handler for our form called submitForm. Lets write this function:

  • first get all data the user has input to the form
  • then build a URL for submission (we have to include the Id)
  • then submit the form to the server
  • and if we were succesful, refresh the Tableau dashboard so the user can see the change.
submitForm = (e)->
  # dont follow up
  e.preventDefault()
  # Collect the form data
  formData = getFormFields('#editor-form')
  # replace the submit url with the proper fields
  submit_url = $(this).data('url').replace /\{\{([a-z_]+)\}\}/g, (m, name)-> formData[name]

  $.get(submit_url, _.pick(formData, "id", "quantity", "comment"))
    .done ()->
      # Update the tableau workbook after we have the data
      getCurrentViz().refreshDataAsync()
    .fail (err)-> console.error "Error getting the data:", err.message, err.stack

The only tricky part here is using the data-url attribute of our submit control to tell us where we want to submit our form (we could have set the forms action attribute if we want to be semantically correct about that, but since we are templating the string, that would result in a disconnect between the semantical meaning of the action attribute and the URL it actually calls).

And our POC should be complete at this point.

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