As a user I want to change a task to a different type as an element template is applied

Is your feature request related to a problem? Please describe

As I model my diagram I tend to start with plain tasks rather than executable, i.e. bpmn:ServiceTask ones. Everything else does slow me down because I’d have to manually make each of my tasks a service task.

As I make my diagram executable I’m revising each task, making it either a service task, business rule task, …

What I wanted to do is to apply a “mail task” template on a blank task; that template shall make the task a bpmn:ServiceTask before applying the template. If it was not a camunda:ServiceTaskLike or zeebe:ServiceTaskLike it was not executable by the engine.

What I have to do is to manually change the task to be a service task first, which is annoying. A unneeded indirection:

Camunda Modeler v5 screen capture, showcasing ServiceTask -> REST task transition required.

Furthermore, when searching for an element template, the service task template wouldn’t even show up for blank tasks, which makes it harder to discover.

Describe the solution you’d like

• Be able to configure a type binding for an element template; if it does not match with the current task the task is morphed into the target type before the other element template properties are applied
• Given a type binding, also display these element templates on template select (maybe as a follow up action)

➡️ Goal: Make it quicker to make a task executable backed by an element template.

Describe alternatives you’ve considered

Consider the current limitation a feature, not a bug.

Additional context

Came up in the context of connectors, specifically https://github.com/camunda/web-modeler/issues/524.

[marstamm]

RE the JSON schema:

instead of adding the type to the properties array, we can also have it as a root property

  'appliesTo': [
    'bpmn:Task',
    'bpmn:ServiceTask'
  ],
  'elementType': {               // <-- new
    'value': 'bpmn:ServiceTask' 
  }

This ensures that there is only one target type and we don’t have to validate type: 'hidden'. Cf. https://github.com/camunda/element-templates-json-schema/pull/48#issuecomment-1077719731

[nikku]

Would this still be a valid Template […]? As we also check if an element can be applied using the is() utility (includes subclasses) rather than a perfect match, I think we should support this.

I don’t see a reason it should not be (a valid template). Our users should be able to facilitate the full power of our meta-model.