How to handle unknown errors from a model

A how to guide to display a user message when unknown model errors occur.

Introduction

When a model is computed as part of your solution it might fail for unknown reasons. Such reasons might include:

A problem with the user’s access rights
A hickup in the user’s internet connection
An execution timeout or unhandled execution error

Regardless of the cause, it is a good idea to help the user understand what is going on. This guide focusses on setting up a so called snackbar notification message for such events. It is advised to always include this for your models.

A word on the model error status

This guide refers to the model error status. This status should not be confused with the model having errors (think orange or red boxes in the Grasshopper UI). In general, when a model contains errors it still computes with a success status. In this case some of the outputs of which their upstream components had errors might be empty. It is advised to think about these scenarios and handle them in your solution accordingly (e.g. output warning and error messages).

When a model computes with the error status it generally indicates a more system related issue, which may or may not be temporary (see examples above).

Prerequisites

You know How to set up a solution.
You know How to define the pages and their flow.
You know How to add parametric inputs to your solution.

1. Setup your solution with model and controls

Let’s start with a solution that contains a model with a single input named value which is controlled by a corresponding text input in a control panel

kind: Frame
contents:
  model:
    kind: Model
    modelFile: model.gh
    subscribe:
      - kind: ControlPanel
        frame: main
        source: controls
  controls:
    kind: ControlPanel
    controls:
      value:
        kind: TextInput
        placeholder: Please provide a value

2. Add the snack bar

When this model fails we would like to inform the user of this. To do this we can add a SnackBar block and subscribe it to the model error status:

message:
  kind: SnackBar
  subscribe:
    - kind: Model
      frame: main
      source: model
      onStatus: error
      message:
        kind: StaticMessage
        message: The model failed to solve

Of course the message displayed may be customized to your needs to better inform the user.

In the event of a model error the user will see the following message:

Configuration

See the SnackBar block documentation for more information.