User Story (Required on creation):

I can use a Delegate Expression as a Sequence Flow condition. Currently, it is only possible to define a JUEL expression or a script evaluating true or false as a condition type. Defining a Delegate Expression would allow writing a Sequence Flow condition in Java, which is handy, especially when using the Spring Boot Starter.

Functional Requirements (Required before implementation):

• The BPMN XML model is extended by the attribute camunda:delegateExpression
• Camunda Modeler supports it

Technical Requirements (Required before implementation):

-

Limitations of Scope (Optional):

1. Support delegate expression only (resolving beans)
2. Additionally support referencing a Java class (seems sensible for consistency reasons)

Alternative solutions

1. A delegate expression can be referenced in the existing sequence flow condition type "expression"
   • Pros
     • Low hanging fruit: might be relatively simple to implement; see PR [1]
       • The code changes in the codebase are relatively straight-forward
     • No changes in Camunda Modeler
     • Documentation effort is low
   • Cons
     • As far as I can see, right now, we don't just reuse JUEL expression attributes to allow resolving delegate beans => this would break consistency and would be super confusing for users
       • This argument against it outweighs those for it
2. A delegate expression can be referenced in any existing JUEL expression; See prototypical implementation [2]
   • Pros
     • Would enable delegate expressions for any notation element that currently provides support for JUEL expression without adding more delegateExpression attributes to the BPMN model
     • One-time effort that might reduce the effort for future feature requests
       • Since our BPMN coverage is quite complete and we don't see many feature requests in this direction, the argument is rather weak
     • See pros of alternative solution #1
   • Cons
     • The existence of both delegateExpression and expression attributes when the latter covers the functionality of the former might be quite confusing for users
       • If we could remove public API, it might be a nice improvement; however, in the current situation with API guarantees and having delegateExpression already at most places, I don't think it would be an improvement that brings much value
     • Maybe there are breaking changes I cannot oversee right now

Hints (Optional):

-

Original Ticket Submitted by Reporter

Summary

Support For Delegates in Gateway Expressions

Description

See: https://forum.camunda.org/t/gateway-expressions-do-not-support-delegate-executions/26400/4

 

The goal here is to add delegate capability to gateway expressions.

 

Happy to make a PR if we can get this added quickly!

[1] https://github.com/camunda/camunda-bpm-platform/pull/1391
[2] https://github.com/camunda/camunda-bpm-platform/pull/1391#issuecomment-809737635