WDC Tutorial


This tutorial picks up where the Get Started topic left off. If you haven’t already, go back and set up your development environment.

By the end of this tutorial, you’ll have a working WDC that connects to the USGS Earthquake feed and downloads data for earthquakes that occurred in the last week.

You’ll learn how to:

If you really want to skip all of this and go straight to the source code, look for the earthquakeUSGS files in the Examples directory. You’ll get a lot more out of this if you build it from scratch though–promise!

Note: The connector that we’ll create in this tutorial (earthquakeWDC) has a different name than the same connector in the Examples directory (earthquakeUSGS). This is to minimize the chances of accidentally overwriting the existing sample. However, if you copy the existing sample, you’ll have to change file paths.

Note: The browser used inside Tableau is QT WebKit, which does not natively support new ES6 features. If you wish to take advantage of newer features (such as promises) when building WDCs you will need to use a polyfill.

Create the HTML page

When you open a WDC in Tableau, you display an HTML page that links to your JavaScript code and to the WDC library. Optionally, this page can also display a user interface for your users to select the data that they want to download.

Create a new file named earthquakeWDC.html and save it in the top-level directory of the webdataconnector repository. (This is the same directory as the README.)

Then, copy the following code into the file:

<html>

<head>
    <title>USGS Earthquake Feed</title>
    <meta http-equiv="Cache-Control" content="no-store" />

    <link href="https://maxcdn.bootstrapcdn.com/bootstrap/3.3.6/css/bootstrap.min.css" rel="stylesheet" crossorigin="anonymous">
    <script src="https://ajax.googleapis.com/ajax/libs/jquery/1.11.1/jquery.min.js" type="text/javascript"></script>
    <script src="https://maxcdn.bootstrapcdn.com/bootstrap/3.3.6/js/bootstrap.min.js" crossorigin="anonymous"></script>

    <script src="https://connectors.tableau.com/libs/tableauwdc-2.3.latest.js" type="text/javascript"></script>
    <script src="earthquakeWDC.js" type="text/javascript"></script>
</head>

<body>
    <div class="container container-table">
        <div class="row vertical-center-row">
            <div class="text-center col-md-4 col-md-offset-4">
                <button type="button" id="submitButton" class="btn btn-success" style="margin: 10px;">Get Earthquake Data!</button>
            </div>
        </div>
    </div>
</body>

</html>

Let’s run through what the code is doing. Skipping over the standard markup for an HTML page, you’ll notice the following between the head tags:

Between the body tags, there is a simple button element that illustrates how users can interact with your connector before getting data. In a later step, you’ll attach an event listener to the button in the JavaScript code.

Create the connector object

Now that you’ve created a user interface, it’s time to write the JavaScript code for the connector. Create a new file named earthquakeWDC.js and save it in the same directory as the earthquakeWDC.html file.

Copy the following code into the file to create the basic structure of the connector:

(function () {
    var myConnector = tableau.makeConnector();

    myConnector.getSchema = function (schemaCallback) {

    };

    myConnector.getData = function (table, doneCallback) {

    };

    tableau.registerConnector(myConnector);
})();

Some things to note about the code:

Add an event listener

Remember how we added a button to the HTML page? It’s time to create an event listener that responds to clicking on the button.

Copy the following code and paste it directly below the registerConnector function:

$(document).ready(function () {
    $("#submitButton").click(function () {
        tableau.connectionName = "USGS Earthquake Feed";
        tableau.submit();
    });
});

Here’s what is going on in the code snippet:

Tip: Not every connector needs a user interface. If you want a connector to run without user input, you can use custom initialization code. For more information, see Custom Initialization and Shutdown

Test the connector so far

The connector doesn’t do very much so far, but it’s enough that we can run it in the simulator.

Note: Have you followed the steps in the Getting Started topic to set up the simulator? This section assumes that you’ve installed dependencies already.

  1. Open a command prompt or terminal in the top-level directory for the webdataconnector repository.

  2. Run npm start to run the test server.

  3. Open a browser and navigate to the following URL:

    http://localhost:8888/Simulator/index.html
    
  4. In the WDC URL field, enter the path to your WDC relative to the simulator. For example, if you created your WDC in the top-level directory, you might enter:

    ../earthquakeWDC.html
    
  5. Click the Start Interactive Phase button. The connector page appears in a new window.

  6. Click Get Earthquake Data!. The connector page closes.

At this point, you might be thinking “Well…did it work?” Let’s add a log message so that you can practice debugging the connector.

Add a log message to confirm it is working (sort of)

  1. In the earthquakeWDC.js file, copy the following code and replace the empty myConnector.getSchema function:

    myConnector.getSchema = function (schemaCallback) {
        tableau.log("Hello WDC!");
    };
    

    The tableau.log function allows you to pass messages from your connector back to the simulator. These log messages are then printed with the browser’s built-in console.log() function on the simulator page.

  2. Refresh the simulator page in your browser.
  3. Open your browser’s developer tools. For example, in Chrome you can press Ctrl+Shift+I.
  4. Click Start Interactive Phase.
  5. Click Get Earthquake Data!.

If all goes well, you should see Hello WDC! in your browser’s console.

Define a schema

So the connector is working now–sort of. Before you can download data and pass it to Tableau, you need to define how you want to map the data to one or more or tables. This mapping of data is done in the schema.

To decide what data you want to map in the schema, you can take a look at the USGS description of the JSON data source: GeoJSON Summary Format. Rather than map all the data available from the data source, this example has selected a focused subset.

When you’re done looking at the summary of the JSON data source, copy the following code into the earthquakeWDC.js file and replace the placeholder getSchema function:

myConnector.getSchema = function (schemaCallback) {
    var cols = [{
        id: "id",
        dataType: tableau.dataTypeEnum.string
    }, {
        id: "mag",
        alias: "magnitude",
        dataType: tableau.dataTypeEnum.float
    }, {
        id: "title",
        alias: "title",
        dataType: tableau.dataTypeEnum.string
    }, {
        id: "location",
        dataType: tableau.dataTypeEnum.geometry
    }];

    var tableSchema = {
        id: "earthquakeFeed",
        alias: "Earthquakes with magnitude greater than 4.5 in the last seven days",
        columns: cols
    };

    schemaCallback([tableSchema]);
};

Here’s what’s going on in the code:

Note: The API Reference describes the properties that you can define for the table object and for each object in the table columns in more detail. For now, let’s plunge ahead to the exciting part–getting the data!

Get the data

Once the schema is defined, you can begin getting data and passing it to Tableau.

Copy the following code and replace the placeholder getData function:

myConnector.getData = function(table, doneCallback) {
    $.getJSON("https://earthquake.usgs.gov/earthquakes/feed/v1.0/summary/4.5_week.geojson", function(resp) {
        var feat = resp.features,
            tableData = [];

        // Iterate over the JSON object
        for (var i = 0, len = feat.length; i < len; i++) {
            tableData.push({
                "id": feat[i].id,
                "mag": feat[i].properties.mag,
                "title": feat[i].properties.title,
                "location": feat[i].geometry
            });
        }

        table.appendRows(tableData);
        doneCallback();
    });
};

Whew! That’s a good-sized chunk of code. Let’s see what’s happening:

See it in action

By now, you’re a pro at running the simulator, so fire it up, load your connector, and click Get Earthquake Data! like before. Now that we have a getSchema function properly defined, you should see the schema displayed in the simulator.

The moment you’ve been waiting for is here! Click Fetch Table Data to run your getData function and display the results in a table.

"The earthquake data is displayed in a table on the simulator page."

Note The location information for an earthquake is returned as a JSON object, which is why you might see object Object displayed in the simulator. Tableau 10.4 added support for geoJSON data, so while the simulator only knows you have some kind of JSON object, Tableau will have no trouble parsing the coordinates from the geometry data.

To really see things working, open your connector in Tableau:

"The earthquake data is displayed on a map in Tableau."

You did it! Nice work. But this is no time to rest on your laurels–try your connector in Tableau, dig into the Examples directory to see more connectors, or read through the WDC documentation. You might want to start by learning about connectors with multiple tables, incremental refresh, and authentication.

Better yet, dive right in and create your own connector!