This how-to describes how to configure the sensor data subscription in the Mendix Logistics IoT app.
This how-to will teach you how to do the following:
- Configure the sensor data subscription
Before starting with this how-to, make sure you have completed the following prerequisite:
- Use the previous how-to in this series: Step 1: Connect App Pages
3 Configuring the Sensor Data Subscription (Step 2)
In this section, you will connect a shipment to an IoT device so the data that the device is generating can be used.
To configure the sensor data subscription, follow these steps:
- In the Desktop Modeler, open the Shipment_Detail page.
Right-click the left-side column of the layout grid (in which Movement and Temperature are also located) and select Add widget > Button > Call microflow button (note that a microflow allow you to express the logic of your application and functions as a visual way of expressing what traditionally ends up in textual program code):
In the Select Microflow dialog box, select the IVK_Subscribe microflow (you can find it by typing IVK_Subscribe in the Filter input box).
Double-click the button and enter Subscribe for the caption.
Right-click the button and select Go to microflow to inspect the microflow.
- When invoking a microflow, you can pass the context of a page to it. That enables you to work with all the data associations from the context objects. In this case, the context object is Shipment. You can view the structure of the Shipment object, which is called an entity, by right-clicking the Shipment input parameter and selecting the Go to entity option. The Shipment is associated to other entities like Alert and Topic, which means that objects from different entities are related to each other. The relation between a Shipment object and a Topic object and the relation between a Topic object and an IoTPlatformConfiguration object enables retrieval of the data required for connecting to AWS.
- Return to the microflow to see what is happening there. In the farthest left activity, the Topic object is retrieved over its association to the Shipment object. It is a best practice to check that the association is not empty. If that is true, the microflow retrieves the IoTPlatformConfiguration object that is associated to the topic. The microflow must then check if there is an IoTPlatformConfiguration object available. If that is true, the data from those objects is used in the subscribe action (via the AWS IoT Connector, which is available in the Mendix App Store). In the subscribe activity, a microflow action is configured for the subscription to the topic on AWS. So, everytime new data is published on that topic, AWS will send a message to the app with that data and trigger this microflow.
Double-click the Data - Subscribe to MQTT topic activity and for the On message microflow, click Show to display the microflow from the details of the connector action.
In the IVK_OnMessage_LogResponse microflow, there are two parameters: Topic (string) and Payload (string). You must log both parameters in the Console to verify that you are receiving the data (if the Console is not open, select View > Console).
Save the changes, click Run Locally, then click View.
Refresh the app in the browser, then click Subscribe and notice that you get a confirmation message. At this point you won’t see anything happening in the app as you configured the app to log the messages it receives from AWS.
Return to the Desktop Modeler and observe the Console. Double-click the log message Sensor data received, which will open the View Log Line Details pop-up window, where you can see the Topic and Payload (JSON) in the Message section. Receiving this kind of log message means you have just connected to AWS and are receiving real-world data!
Now that you have the sensor data subscription set up, go through Step 3: Handle the Sensor Data to learn about processing the data and making it visible in the app.