Debugging Microflows

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The Mendix Modeler has a built-in consistency checker that validates if the application you are building contains any obvious errors. This reduces the amount of technical errors during run-time dramatically, but the Mendix Modeler isn’t able to check if your application contains functional errors. This is mainly a manual practice, but Mendix does support enough tools to make your live easy on this. If you run into a functional error in any of the Microflows, you can easily debug them with the debugger.

1. Preparation

Before starting this how-to please complete the following prerequisites:

2. Debugging Overview

There are three debugging windows to be aware of: breakpoints, debugger and variables

The breakpoints window will show all the Microflows that contain breakpoints. This makes it easier to find your breakpoints. It is best practice to remove any breakpoints after you are done troubleshooting your Microflows. You can always delete them from the breakpoints dock window.

The debugger dock window is useful when you are debugging your Microflow and it will walk you through the Microflow.

The variables dock window shows the variables involved in your Microflow and how they are changing as you step through the Microflow via the debugger window.

3. Using Breakpoints

Breakpoints are points in a microflow where the application will halt execution. This is useful to analyze the application execution and data up to that point. You can add breakpoints at any point in your Microflow by following the steps below.

  1. Run your application locally.
  2. Open the Microflow that needs debugging in the Mendix Modeler.
  3. Right click any of the activities or splits in the Microflow and select Add breakpoint. This sets a breakpoint on the selected step in the Microflow, visually represented by a red stop sign. You can open an overview of all the breakpoints by going to View > Breakpoints:

    In this overview you can enable/disable and delete breakpoints. You can also configure a breakpoint condition and open the Microflow that contains the breakpoint.

4. Debugging

  1. Run the application.
  2. Open the application in your browser and do whatever is needed to trigger the Microflow that you want to debug. As an end user of the application you will see progress bar on your application.  As a developer you will notice that the Mendix icon will be flashing on the windows task bar.
  3. Click the icon on the windows task bar to open the Mendix Modeler. The element with the breakpoint that interrupts this Microflow should be highlighted with a red border.
  4. Open the Debugger from the View menu.

    The Debugger can be used to go through the Microflow step-by-step.

  5. Click Step into or Step over to move on the next step in the Microflow. The difference between ‘Step into’ and ‘Step over’ is only noticeable if you run into a ‘Call Microflow’ activity or ‘Loop’. ‘Step into’ means that the debugger steps into the sub Microflow or Loop and ‘Step over’ just moves the debugger to the next step in the same Microflow.

    With ‘Step out’ you can instruct the debugger to leave the sub Microflow or Loop. It’s basically the opposite of ‘Step Into’.

    Clicking ‘Continue’ instructs the debugger to continue until it reaches another breakpoint.

5. Variable Viewer

As you are stepping through a Microflow the variables window will start to change. This overview will show you all the variables involved in the application. It will show you all the entities, references, current user information and device type information. It is useful as you are stepping through the Microflow to review the variable values and see if they are matching your expectations.

  1. Open the variable viewer from the View menu.

    The Variable Viewer can be used to inspect values of variables in the Microflow. The values are updated with every step you make in the Debugger.

6. Breakpoint Conditions

Sometimes it’s needed to configure a breakpoint in such a way that the Microflow only breaks on a certain condition. This can be achieved with breakpoint conditions. This is configured by use of Microflow expressions. Setting a breakpoint condition can be very handy if you are debugging a batch process and you only want to break at a certain value. It is strongly advised to use breakpoint conditions if you are debugging an application that is running in production. This prevents the application stopping for other users than yourself.

  1. Right click the activity or split in the Microflow with a breakpoint and select Edit breakpoint condition…
  2. Use the following expression to make sure that this breakpoint only interrupts the Microflow if you are executing it yourself. Replace ‘YourUserName’ with your own user name.

    $currentUser/name = 'YourUserName'

    The expression should look like this:

  3. Click OK to save the breakpoint condition.